User’s Guide’s Section 1 to Section 8 cover
various aspects of data analysis and visualization with ParaView.
Reference Manual’s Section 1 to Section 12 provide
details on various components in the UI and the scripting API.
Tutorials are split into Self-directed Tutorial and Classroom Tutorials:
Self-directed Tutorial’s Section 1 to
Section 5 provide an introduction to the ParaView software and its history,
and exercises on how to use ParaView that cover basic usage, batch python scripting and visualizing large
models.
Classroom Tutorials’s Section 1 to Section 18 provide
beginning, advanced, python and batch, and targeted tutorial lessons on how to use ParaView that are presented
as a 3-hour class internally within Sandia National Laboratories.
ParaView is an open-source, multi-platform scientific data analysis and
visualization tool that enables analysis and visualization of extremely large
datasets. ParaView is both a general purpose, end-user application with a
distributed architecture that can be seamlessly leveraged by your desktop or other
remote parallel computing resources and an extensible framework with a
collection of tools and libraries for various applications including scripting
(using Python), web visualization (through ParaViewWeb), or in-situ analysis
(with Catalyst).
ParaView leverages parallel data processing and rendering to enable interactive
visualization for extremely large datasets. It also includes support for large
displays including tiled displays and immersive 3D displays with head tracking
and wand control capabilities.
ParaView also supports scripting and batch processing using Python. Using
included Python modules, you can write scripts that can perform almost all the
functionality exposed by the interactive application and much more.
ParaView is open-source (BSD licensed, commercial software friendly). As with
any successful open-source project, ParaView is supported by an active user
and developer community. Contributions to both the code and this user’s manual
that help make the tool and the documentation better are always welcome.
Did you know?
The ParaView project started in 2000 as a collaborative effort between Kitware
Inc. and LANL. The initial funding was provided by a
three year contract with the US Department of Energy ASCI Views program. The
first public release, ParaView 0.6, was announced in October 2002.
Independent of ParaView, Kitware started developing a web-based visualization
system in December 2001. This project was funded by Phase I and II SBIRs from
the US ARL and eventually became the PVEE.
PVEE significantly contributed to the development of ParaView’s
client/server architecture. PVEE was the precursor to ParaViewWeb, a modern
web visualization solution based on ParaView.
Since the project began, Kitware has successfully collaborated with
Sandia, LANL, the ARL, and
various other academic and government institutions to continue development. Today, the
project is still going strong!
In September 2005, Kitware, Sandia National Labs and CSimSoft started the
development of ParaView 3.0. This was a major effort focused on rewriting the
user interface to be more user friendly and on developing a quantitative
analysis framework. ParaView 3.0 was released in May 2007.
This user’s manual is designed as a guide for using the ParaView application. It is
geared toward users who have a general understanding of common data
visualization techniques. For scripting, a working knowledge of the Python
language is assumed. If you are new to Python, there are several tutorials and
guides for getting started that are available on the Internet.
Did You Know?
In this guide, we will periodically use these Did you know? boxes to provide
additional information related to the topic at hand.
Common Errors
Common Errors blocks are used to highlight some of the common problems or
complications you may run into when dealing with the topic of discussion.
This guide is split into three volumes:
User’s Guide’s Section 1 to Section 8 cover
various aspects of data analysis and visualization with ParaView.
Reference Manual’s Section 1 to Section 12 provide
details on various components in the UI and the scripting API.
Tutorials are split into Self-directed Tutorial and Classroom Tutorials:
Self-directed Tutorial’s Section 1 to
Section 5 provide an introduction to the ParaView software and its history,
and exercises on how to use ParaView that cover basic usage, batch python scripting and visualizing large
models.
Classroom Tutorials’s Section 1 to Section 18 provide
beginning, advanced, python and batch, and targeted tutorial lessons on how to use ParaView that are presented
as a 3-hour class internally within Sandia National Laboratories.
This guide tries to cover most of the commonly used functionality in ParaView.
ParaView’s flexible, pipeline-based architecture opens up numerous possibilities.
If you find yourself looking for some feature not covered in this guide, refer to
the Wiki pages or to the ParaView Discourse
forum, specially the
FAQ and the
Tips and Tricks categories.
Also feel free to ask about it under the relevant
Support category.
ParaView is open source. The complete source code for all the functionality
discussed in The ParaView Guide can be downloaded from the ParaView website
http://www.paraview.org. We also provide binaries for the major platforms:
Linux, Mac OS X, and Windows. You can get the source files and binaries for the
official releases, as well as follow ParaView’s active development, by downloading the
nightly builds.
Visualization model: Process objects A, B, and C input
and/or output one or more data objects. Data objects
represent and provide access to data; process objects
operate on the data. Objects A, B, and C are source, filter, and mapper objects,
respectively. [SML96]
Visualization is the process of converting raw data into images and renderings
to gain a better cognitive understanding of the data. ParaView uses VTK, the
Visualization Toolkit, to provide the backbone for visualization and data processing.
The VTK model is based on the data-flow paradigm. In this paradigm,
data flows through the system being transformed at each step by modules known as
algorithms. Algorithms could be common operations such as clipping, slicing,
or generating contours from the data, or they could be computing derived
quantities, etc. Algorithms have input ports through which they take in data and
output ports through which they produce output. You need producers that ingest
data into the system. These are simply algorithms that do not have an input port but have one or
more output ports. They are called sources . Readers that read data
from files are examples of such sources. Additionally, there are algorithms that
transform the data into graphics primitives so that they can be rendered on a
computer screen or saved to disk in another file. These algorithms, which have one
or more input ports but do not have output ports, are called
sinks . Intermediate
algorithms with input ports and output ports are called
filters . Together, sources,
filters, and sinks provide a flexible infrastructure wherein you can
create complex processing pipelines by simply connecting algorithms to
perform arbitrarily complex tasks.
For more information on VTK’s programming model, refer
to [SML96].
This way of looking at the visualization pipeline is at the core of ParaView’s
work flow: You bring your data into the system by creating a reader – the
source. You then apply filters to either extract information
(e.g., iso-contours) and render the results in a view or to save the data to disk using
writers – the sinks.
ParaView includes readers for a multitude of file formats typically used in the
computational science world. To efficiently represent data from various fields
with varying characteristics, VTK provides a rich data model that ParaView uses.
The data model can be thought of simply as ways of representing data in memory.
We will cover the different data types in more detail in
Section 3.1. Readers produce a data type suitable for
representing the information the files contain. Based on the data type, ParaView
allows you to create and apply filters to transform the data. You can also show the data
in a view to produce images or renderings. Just as there are several types of
filters, each perfoming different operations and types of processing, there are several kinds
of views for generating various types of renderings including 3D surface views,
2D bar and line views, parallel coordinate views, etc.
Did You Know?
The Visualization Toolkit (VTK) is an open-source, freely available software
system for 3D computer graphics, modeling, image processing, volume rendering,
scientific visualization, and information visualization. VTK also includes
ancillary support for 3D interaction widgets, two and three-dimensional
annotation, and parallel computing.
At its core, VTK is implemented as a C++ toolkit, requiring users to build
applications by combining various objects into an application. The system also
supports automated wrapping of the C++ core into Python, Java, and Tcl so that
VTK applications may also be written using these interpreted programming
languages. VTK is used world-wide in commercial applications, research and
development, and as the basis of many advanced visualization applications such
as ParaView, VisIt, VisTrails, Slicer, MayaVi, and OsiriX.
This is the main ParaView graphical user interface
(GUI). In most cases, when we refer to ParaView, we are indeed talking about
this application. It is a Qt-based, cross-platform UI that provides access to the
ParaView computing capabilities. Major parts of this guide are dedicated to
understanding and using this application.
Similar to pvpython, pvbatch is also a Python
interpreter that runs Python scripts for ParaView. The one difference is that, while
pvpython is meant to run interactive scripts, pvbatch
is designed for batch processing. Additionally, when running on computing
resources with MPI capabilities, pvbatch can be run in parallel. We
will cover this in more detail in Section 7.10.
For remote visualization, this executable represents the server that does all
of the data processing and, potentially, the rendering.
You can make paraview connect to
pvserver running remotely on an HPC resource. This allows you to
build and control visualization and analysis on the HPC resource from your
desktop as if you were simply processing it locally on your desktop!
These can be thought of as the pvserver split into two separate
executables: one for the data processing part, pvdataserver, and
one for the rendering part, pvrenderserver. Splitting these into
separate processes makes it possible to perform data processing and rendering on
separate sets of nodes with appropriate computing capabilities suitable for the
two tasks. Just as with pvserver, paraview can
connect to a pvdataserver- pvrenderserver pair for
remote visualization. Unless otherwise noted, all discussion of remote visualization or
client-server visualization in this guide is applicable to both
pvserver and pvdataserver - pvrenderserver configurations.
paraview is the graphical front-end to the ParaView application. The
UI is designed to allow you to easily create pipelines for data processing with
arbitrary complexity. The UI provides panels for you to inspect and modify
the pipelines, to change parameters that in turn affect the processing pipelines,
to perform various data selection and inspection actions to introspect the data,
and to generate renderings. We will cover various aspects of the UI
for the better part of this guide.
Let’s start by looking at the various components of the UI. If you run
paraview for the first time, you will see something similar to the
Fig. 1.2. The UI is comprised of menus,
dockable panels, toolbars, and the viewport – the central portion of the
application window.
Menus provide the standard set of options typical with a desktop application
including options for opening/saving files (File
menu), for undo/redo (Edit menu), for the toggle panel, and for toolbar visibilities
(View menu). Additionally, the menus provide ways to create sources that
generate test datasets of various types (Sources menu), as well new
filters for processing data (Filters menu). The Tools menu
provides access to some of the advanced features in paraview such as
managing plugins and favorites.
Panels provide you with the ability to peek into the application’s state. For example, you can
inspect the visualization pipeline that has been set up ( PipelineBrowser ), as well as the memory that is being used ( MemoryInspector ) and the parameters or properties
for a processing module ( Properties panel). Several of the panels also
allow you to change the values that are displayed, e.g., the Properties panel not only
shows the processing module parameters, but it also allows you to change them.
Several of the panels are context sensitive. For example, the Properties
panel changes to show the parameters from the selected module as you change the
active module in the PipelineBrowser .
Toolbars are designed to provide quick access to common functionality. Several
of the actions in the toolbar are accessible from other locations,
including menus or panels. Similar to panels, some of the toolbar buttons are
context sensitive and will become enabled or disabled based on the selected
module or view.
The viewport or the central portion of the paraview window is the
area where ParaView renders results generated from the data. The containers in
which data can be rendered or shown are called views. You can create
several different types of views, all of which are laid out in this viewport
area. By default, a 3D view is created, which is one of the most commonly used
views in ParaView.
To gain a better understanding of how to use the application interface, let’s
consider a simple example: creating a data source and applying a filter to it.
The visualization process in ParaView begins by bringing your data into the
application. Section 2 explains how to read data from
various file formats. Besides reading files to bring in data into the
application, ParaView also provides a collection of data sources that can
produce sample datasets. These are available under the Sources menu. To
create a source, simply click on any item in the Source menu.
Did You Know?
As you move your cursor over the items in any menu, on most platforms (except
Mac OS X), you’ll see a brief description of the item in the status bar on the
lower-left corner in the application window.
If you click on Sources > Sphere, for example,
you’ll create a producer algorithm that generates a spherical surface, as shown in
Fig. 1.3.
A pipeline module is added in the PipelineBrowser panel with a name derived from the menu item, as is highlighted.
The Properties panel fills up with text to indicate that it’s showing properties for the highlighted item (which, in this case, is Sphere1 ), as well as to display some widgets for parameters such as Center , Radius , etc.
On the Properties panel, the Apply button becomes enabled and highlighted.
The 3D view remains unaffected, as nothing new is shown or rendered in this view as of yet.
Let’s take a closer look at what has happened. When we clicked on
Sources > Sphere, referring to
Section 1.2, we created an instance of a source that
can produce a spherical surface mesh – that’s what is reflected in the
PipelineBrowser .
This instance receives a name, which is used by the Sphere1 and the PipelineBrowser , as well as other
components of the UI, to refer to this instance of the source. Pipeline
modules such as sources and filters have parameters on them that you can change
that affect that module’s behavior. We call them properties. The
Properties panel shows these properties and allows you to change them.
Since the ingestion of data into the system can be a time-consuming process,
paraview allows you to change the properties before the module
executes or performs the actual processing to ingest the data. Hence, the
Apply button is highlighted to indicate that you need to accept the
properties before the application will proceed. Since no data has entered the
system yet, there’s nothing to show. Therefore, the 3D view remains unaffected.
Let’s assume we are okay with the default values for all of the properties on the
Sphere1 . Next, click on the Apply button.
Let’s assume we are okay with the default values for all of the properties on the
Sphere1. Next, click on the Apply button.
The Apply button goes back to its old disabled/un-highlighted state.
A spherical surface is rendered in the 3D view.
The Display section on the Properties panel now shows new parameters or properties.
Certain toolbars update, and you can see that toolbars with text, such as SolidColor and Surface , now become enabled.
By clicking Apply , we told paraview to apply the properties
shown on the Properties panel. When a new source (or filter) is
applied for the first time, paraview will automatically show
the data that the pipeline module produces in the current view, if possible.
In this case, the sphere source produces a surface mesh, which is then shown or
displayed in the 3D view.
The properties that allow you to control how
the data is displayed in the view are now shown on the Properties panel in
the Display section. Things such as the surface color, rendering type or
representation, shading parameters, etc., are shown under this newly updated
section. We will look at display properties in more detail in
Section 4.
Some of the properties that are commonly used are also duplicated in the
toolbar. These properties include the data array with which the surface is colored and the representation
type. These are the changes in the toolbar that allow you to quickly change some
display properties.
If you change any of the properties on the sphere source, such as the properties
under the Properties
section on the Properties panel, including the Radius
for the spherical mesh or its Center , the Apply button will be
highlighted again. Once you are finished with all of the property changes, you can
hit Apply to apply the changes. Once the changes are applied,
paraview will re-execute the sphere source to produce a new mesh,
as requested. It will then automatically update the view, and you will see the
new result rendered.
If you change any of the display properties for the sphere source, such as the
properties under the Display section of the Properties panel (including
Representation or Opacity ), the Apply button is not affected, the
changes are immediately applied, and the view is updated.
The rationale behind this is that, typically, the execution of the source (or
filter) is more computationally intensive than the rendering. Changing source (or
filter) properties causes that algorithm to re-execute, while changing display
properties, in most cases, only triggers a fresh render with an updated graphics
state.
Did You Know?
For some workflows with smaller data sizes, it may be more convenient
if the Apply button was automatically applied even after changes are made to the
pipeline module properties. You can change this from the application settings dialog, which is
accessible from the Edit > Settings menu. The setting is called AutoApply .
You can also change the AutoApply state using the
button from the toolbar.
As per the data-flow paradigm, one creates pipelines with
filters to transform data. Similar to the Sources menu, which allows us to
create new data sources, there’s a Filters menu that provides access to
the large set of filters that are available in ParaView. If you peruse the
items in this menu, some of them will be enabled, and some of them will be
disabled. Filters that can work with the data type being produced by the sphere
source are enabled, while others are disabled. You can click on any of the
enabled filters to create a new instance of that filter type.
Did You Know?
To figure out why a particular filter doesn’t work with the current source,
simply move your mouse over the disabled item in the Filters menu. On
Linux and Windows (not OS X, however), the status bar will provide a brief
explanation of why that filter is not available.
For example, if you click on Filters > Shrink, it will create a filter
that shrinks each of the mesh cells by a fixed factor. Exactly as before, when we
created the sphere source, we see that the newly-created filter is given a new
name, Shrink1 , and is highlighted in the PipelineBrowser . The
Properties panel is also updated to show the properties for this new
filter, and the Apply button is highlighted to request that we accept the
properties for the filter so that it can be executed and the result can be rendered. If you
click back and forth between the Sphere1 and Shrink1 in the
PipelineBrowser , you’ll see the Properties panel and toolbars update,
reflecting the state of the selected pipeline module. This is an important
concept in ParaView. There’s a notion of active pipeline module, called the
active source .
Several panels, toolbars, and menus will update based on
the active source.
If you click Apply , as was the case before, the shrink filter will be executed and the
resulting dataset will be generated and shown in the 3D view. paraview
will also automatically hide the result from the Sphere1 so that it is not shown
in the view. Otherwise, the two datasets will overlap. This is reflected by
the change of state for the eyeball icons in the PipelineBrowser
next to each of the pipeline modules. You can show or hide results from any
pipeline module by clicking on the eyeballs.
This simple workflow forms the basis of all the data analysis and visualization
in ParaView. The process involves creating sources and filters, changing their
parameters, and showing the generated result in one or more views. In the rest of
this guide, we will cover various types of filters and data processing that you
can do. We will also cover different types of views that can help you produce a wide array of 2D
and 3D visualizations, as well as inspect your data and drill down into it.
Common Errors
Beginners often forget to hit the Apply button after creating sources or
filters or after changing properties. This is one of the most common pitfalls for
users new to the ParaView workflow.
While this section refers to pvpython, everything that we discuss
here is applicable to pvbatch as well. Until we start looking into
parallel processing, the only difference between the two executables is that
pvpython provides an interactive shell wherein you can type your
commands, while pvbatch expects the Python script to be specified
on the command line argument.
ParaView provides a scripting interface to write scripts for performing the
tasks that you could do using the GUI. The scripting interface can be
accessed through Python, which is an interpreted programming language popular
among the scientific community for its simplicity and its capabilities. While a
working knowledge of Python will be useful for writing scripts with advanced
capabilities, you should be able to follow most of the discussion in this book
about ParaView scripting even without much Python exposure.
ParaView provides a paraview package with several Python modules that expose
various functionalities. The primary scripting interface is provided by the
simple module.
When you start pvpython, you should see a prompt in a terminal
window as follows (with some platform specific differences).
You can now type commands at this prompt, and ParaView will execute them. To
bring in the ParaView scripting API, you first need to import the simple
module from the paraview package as follows:
>>> fromparaview.simpleimport*
Common Errors
Remember to hit the Enter or Return key after every command to execute
it. Any Python interpreter will not execute the command until Enter is hit.
If the module is loaded correctly, pvpython will present a prompt for the next
command.
>>> fromparaview.simpleimport*>>>
You can consider this as in the same state as when paraview was
started (with some differences that we can ignore for now). The application is
ready to ingest data and start processing.
In paraview, we created the data source by using the Sources
menu. In the scripting environment, this maps to simply typing the name of the
source to create.
>>> Sphere()
This will create the sphere source with a default set of properties. Just like
with paraview, as soon as a new pipeline module is created, it
becomes the active source.
Now, to show the active source in a view, try:
>>> Show()>>> Render()
The Show call will prepare the display, while the Render call will
cause the rendering to occur. In addition, a new window will popup, showing the result
(Fig. 1.5). This is similar to the state after hitting
Apply in the UI.
To change the properties on the sphere source, you can use the SetProperties
function.
# Set a single property on the active source.>>>SetProperties(Radius=1.0)# You can also set multiple properties.>>>SetProperties(Center=[1,0,0],StartTheta=100)
Similar to the Properties panel, SetProperties affects the active
source. To query the current value of any property on the active source, use
GetProperty .
SetProperties and GetProperty functions serve the same function as the
Properties section of the Properties panel – they allow you to set
and introspect the pipeline module properties for the active source.
Likewise, for the Display section of the panel, or the display properties,
we have the SetDisplayProperties and GetDisplayProperty functions.
Note how the property names for the SetProperties and
SetDisplayProperties functions are not enclosed in double-quotes, while
those for the GetProperty and GetDisplayProperty methods are.
In paraview, every time you hit Apply or change a display
property, the UI automatically re-renders the view. In the scripting environment,
you have to do this manually by calling the Render function every time you want
to re-render and look at the updated result.
Similar to creating a source, to apply a filter, you can simply create the filter by
name.
# Create the `Shrink' filter and connect it to the active source# which is the `Sphere' instance.>>>Shrink()# As soon as the Shrink filter is created, it will now become the new active# source. All methods acting on active source now act on this filter instance# and not the Sphere instance created earlier.# Show the resulting data and render it.>>>Show()>>>Render()
If you tried the above script, you’ll notice the result isn’t exactly what we
expected. For some reason, the shrank cells are not visible. This is because we
missed one stage: In paraview, the UI was smart enough to
automatically hide the input dataset for the newly created filter after we hit
apply. In the scripting interface, such operations are the user’s responsibility. We
should have hidden the sphere source from the view. We can use the Hide
method, the counter part of Show , to hide the active source. But, now we have
a problem – when we created the shrink filter, we changed the active source to
be the shrink instance. Luckily, all the functions we discussed so far can take
an optional first argument, which is the source or filter instance on which to operate.
If provided, that instance is used instead of the active source.
The solution is as follows:
# Get the input property for the active source, i.e. the input for the shrink.>>>shrinksInput=GetProperty("Input")# This is indeed the sphere instance we created earlier.>>>print(shrinksInput)<paraview.servermanager.Sphereobjectat0x11d731e90># Hide the sphere instance explicitly.>>>Hide(shrinksInput)# Re-render the result.>>>Render()
Alternatively, you could also get/set the active source using the GetActiveSource and SetActiveSource functions.
>>> shrinkInstance=GetActiveSource()>>> print(shrinkInstance)<paraview.servermanager.Shrink object at 0x11d731ed0># Get the input property for the active source, i.e. the input# for the shrink.>>> sphereInstance=GetProperty("Input")# This is indeed the sphere instance we created earlier.>>> print(sphereInstance)<paraview.servermanager.Sphere object at 0x11d731e90># Change active source to sphere and hide it.>>> SetActiveSource(sphereInstance)>>> Hide()# Now restore the active source back to the shrink instance.>>> SetActiveSource(shrinkInstance)# Re-render the result>>> Render()
Here’s another way of doing something similar to what we did in the previous
section for those familiar with Python and/or object-oriented programming.
It’s totally okay to stick with the previous approach.
>>> fromparaview.simpleimport*>>> sphereInstance=Sphere()>>> sphereInstance.Radius=1.0>>> sphereInstance.Center[1]=1.0>>> print(sphereInstance.Center)[0.0, 1.0, 0.0]>>> sphereDisplay=Show(sphereInstance)>>> view=Render()>>> sphereDisplay.Opacity=0.5# Render function can take in an optional view argument, otherwise it# will simply use the active view.>>> Render(view)>>> shrinkInstance=Shrink(Input=sphereInstance, ShrinkFactor=1.0)>>> print(shrinkInstance.ShrinkFactor)1.0>>> Hide(sphereInstance)>>> shrinkDisplay=Show(shrinkInstance)>>> Render()
When changing properties on the Properties panel in
paraview, we noticed that the algorithm doesn’t re-execute until
you hit Apply . In reality, Apply isn’t what’s actually triggering
the execution or the updating of the processing pipeline. What happens is that
Apply updates the parameters on the pipeline module and causes the view to
render. If the output of the pipeline module is visible in the view, or if the output of
any filter connected to it downstream is visible in the view, ParaView will
determine that the data rendered is obsolete and request the pipeline to
re-execute. It implies that if that pipeline module (or any of the filters
downstream from it) is not visible in the view, ParaView will have no reason to
re-execute the pipeline, and the pipeline module will not be be updated. If, later
on, you do make this module visible in the view, ParaView will automatically
update and execute the pipeline. This is often referred to as
demand-driven pipeline execution . It makes it possible to avoid unnecessary module executions.
In paraview, you can get by without ever noticing this since the
application manages pipeline updates automatically. In pvpython
too, if your scripts are producing renderings in views, you’d never
notice this as long as you remember to call Render . However, you may want
to write scripts to produce transformed datasets or to determine data
characteristics. In such cases, since you may never create a view, you’ll never
be seeing the pipeline update, no matter how many times you change the
properties.
Accordingly, you must use the UpdatePipeline function.
UpdatePipeline updates the pipeline connected to the active source (or only
until the active source, i.e., anything downstream from it, won’t be updated).
>>> fromparaview.simpleimport*>>> sphere=Sphere()# Print the bounds for the data produced by sphere.>>> print(sphere.GetDataInformation().GetBounds())(1e+299, -1e+299, 1e+299, -1e+299, 1e+299, -1e+299)# The bounds are invalid -- no data has been produced yet.# Update the pipeline explicitly on the active source.>>> UpdatePipeline()# Alternative way of doing the same but specifying the source# to update explicitly.>>> UpdatePipeline(proxy=sphere)# Let's check the bounds again.>>> sphere.GetDataInformation().GetBounds()(-0.48746395111083984, 0.48746395111083984, -0.48746395111083984, 0.48746395111083984, -0.5, 0.5)# If we call UpdatePipeline() again, this will have no effect since# the pipeline hasn't been modified, so there's no need to re-execute.>>> UpdatePipeline()>>> sphere.GetDataInformation().GetBounds()(-0.48746395111083984, 0.48746395111083984, -0.48746395111083984, 0.48746395111083984, -0.5, 0.5)# Now let's change a property.>>> sphere.Radius=10# The bounds won't change since the pipeline hasn't re-executed.>>> sphere.GetDataInformation().GetBounds()(-0.48746395111083984, 0.48746395111083984, -0.48746395111083984, 0.48746395111083984, -0.5, 0.5)# Let's update and see:>>> UpdatePipeline()>>> sphere.GetDataInformation().GetBounds()(-9.749279022216797, 9.749279022216797, -9.749279022216797, 9.749279022216797, -10.0, 10.0)
We will look at the sphere.GetDataInformation API in
Section 3.3 in more detail.
For temporal datasets, UpdatePipeline takes in a time argument, which is the
time for which the pipeline must be updated.
# To update to time 10.0:>>>UpdatePipeline(10.0)# Alternative way of doing the same:>>>UpdatePipeline(time=10.0)# If not using the active source:>>>UpdatePipeline(10.0,source)>>>UpdatePipeline(time=10.0,proxy=source)
The paraview application also provides access to an internal shell, in which
you can enter Python commands and scripts exactly as with
pvpython. To access the Python shell in the GUI, use the
View > Python Shell menu option. A dialog will pop up with a
prompt exactly like pvpython. You can try inputting commands from
the earlier section into this shell. As you type each of the commands, you will
see the user interface update after each command, e.g., when you create the
sphere source instance, it will be shown in the PipelineBrowser . If you
change the active source, the PipelineBrowser and other UI components will
update to reflect the change. If you change any properties or display properties, the
Properties panel will update to reflect the change as well!
PythonShell in paraview provides access to the scripting.
Did You Know?
The PythonShell in paraview supports auto-completion for functions
and instance methods. Try hitting the Tab key after partially typing any
command (as shown in Fig. 1.7).
This guide provides a fair overview of ParaView’s Python API. However, there
will be cases when you just want to know how to complete a particular action or
sequence of actions that you can do with the GUI using a Python script instead. To
accomplish this, paraview supports tracing your actions in
the UI as a Python script. Simply start tracing by clicking on
Tools > Start Trace. paraview now enters a mode where all
your actions (or at least those relevant for scripting) are monitored. Any time
you create a source or filter, open data files,
change properties and hit Apply , interact with the 3D scene, or save
screenshots, etc., your actions will be monitored. Once you are done with the series of
actions that you want to script, click
Tools > Stop Trace. paraview will then pop up an editor
window with the generated trace. This will be the Python script equivalent for
the actions you performed. You can now save this as a script to use for batch
processing.
In a visualization pipeline, data sources bring data into the system for
processing and visualization. Sources, such as the Sphere source
(accessible from the Sources menu in paraview),
programmatically create datasets for
processing. Another type of data sources are readers. Readers can read data
written out in disk files or other databases and bring it into ParaView for
processing. ParaView includes readers that can read several of the
commonly used scientific data formats. It’s also possible to write plugins that
add support for new or proprietary file formats.
ParaView provides several sample datasets for you to get started. You can
download an archive with several types of data files from the download page at
https://www.paraview.org/download under the Data section.
To open a data file in paraview, you use the OpenFile dialog.
This dialog can be accessed from the File > Open menu or by using the
button in the MainControls toolbar. You can
also use the keyboard shortcut CTRL + O (or ⌘ + O) to open this dialog.
OpenFile dialog in paraview for opening data (and other) files.
The OpenFile dialog
allows you to browse the file system on the data
processing nodes. This will become clear when we look at using ParaView for
remote visualization. While several of the UI elements in this dialog are
obvious such as navigating up the current directory, creating a new
directory, and navigating back and forth between directories, which can all be done with the
standard system shortcuts like CTRL + N (or ⌘ + N) to create a directory or
Alt + ↑ to go to the parent directory, there are a few things to note.
The Favorites pane shows some platform-specific common locations such as the home
directory and desktop. The favorites directories can be customized from the buttons above
it, which respectively adds the current directory to the favorites, removes the current
directory from the favorites, and resets all the favorites to the system default. Another way to
change which directories are in the favorites is to use the right-click context menus.
Right-clicking any directory in the main list will display a menu with the option to add it to
the favorites. A right-click on a favorite in the favorites list displays the option to remove
it.
The RecentDirectories pane shows a few of the most recently used directories.
You can browse to the directory containing your datasets and either select the
file and hit Ok or simply double click on the file to open it. You can also
select multiple files using the CTRL (or ⌘) key. This will open
each of the selected files separately.
Right-clicking the files list will display a few options, depending on what was right-clicked.
The ShowHiddenFiles is always visible, and can be checked to display the hidden files and
directories.
The Openinfileexplorer is also always present and either opens in the system file
explorer the selected directory if one was right-clicked, or opens the current directory if a
file or nothing was selected.
Selecting a file or a directory adds the Rename option.
Selecting a folder adds the Addtofavorites option which adds the selected directory to
the Favorites pane on the left.
Selecting an empty directory provides the Deleteemptydirectory option.
When a file is opened, paraview will create a reader instance of
the type suitable for the selected file based on its extension. The reader will
simply be another pipeline module, similar to the source we created in
Section 1. From this point forward, the workflow will be
the same as we discussed in Section 1.4.2 :
You adjust the reader properties, if needed, and hit Apply .
paraview will then read the data from the file and render it in the
view.
If you selected multiple files using the CTRL (or ⌘) key,
paraview will create multiple reader modules. When you hit
Apply , all of the readers will be executed, and their data will be shown in the view.
The OpenFile dialog can be used to select a
temporal file series (top) or select multiple files to open separately (bottom).
Did you know?
This ability to hit the Apply button once to accept changes on multiple
readers applies to other pipeline modules, including sources and filters.
In general, you can change properties for multiple modules in a pipeline, and
hit Apply to accept all of the changes at once. It is possible to
override this behavior from the Settings dialog.
Reader selection depending on the selected file types
File dialog “Files of type” to filter which files to show and to change how the reader will be chosen.
When selecting files, the current category for the “Files of type” field
(Fig. 2.3) changes the way the reader will be chosen.
If the “Supported Files” value is selected, if only one reader is available for the type of
file, it will be selected automatically. If multiple readers can be used, the “Open Data With…”
dialog (Fig. 2.4) will appear to choose which reader to use. The “Set
reader as default” button can be clicked to automatically use this reader when one of its pattern
matches a file that could otherwise be opened by multiple readers. When a reader is set as
default, it will be used automatically for files that match its patterns.
OpenDataWith... dialog shown to manually choose the reader to use for a file with multiple available readers.
If the “All Files” value is selected, the same dialog will be displayed with all the existing
readers. If you picked an incorrect reader, however, you’ll get error
messages either when the reader module is instantiated or after you hit
Apply. In either case, you can simply Delete the reader module and try
opening the file again, this time choosing a different reader.
When clicking “Set reader as default”, a line edit will be displayed to set the custom
pattern to use for this reader (Fig. 2.5). This is a standard
wildcard pattern, and multiple patterns can be used by separating them with spaces.
The input to define the pattern to add to the settings to use this reader by default.
If a specific reader is selected, for example “PNG Image Files”, this reader will be
always be used automatically, even if other readers would be available or if the file is matching
a pattern present in the “Default reader details” settings.
Error messages in paraview are shown in the OutputMessages
window (Fig. 2.6).
It is accessible from the View > Output Messages menu.
Whenever there’s a new error message, paraview will
automatically pop open this window and raise it to the top. This window can
be attached, or docked, in the main window so that it is visible with the
other user interface elements without covering them up.
The OutputMessages window is used to show errors, warnings, and other messages raised by the application.
The default readers settings can be seen and modified in the Edit -> Settings menu, and
Miscellaneous tab (Fig. 2.7).
Most datasets produced by scientific simulation runs are temporal in nature.
File formats differ in how this information is saved in the file.
While several file formats support saving multiple timesteps in the same file,
others save them out as a sequence of files, known as a file series
The OpenFile dialog automatically detects file series and shows them as a
grouped element, as shown in Fig. 2.2. To load the file series,
simply select the group, and hit Ok . You can also open a single file in the
series as a regular file. To do so, open the file group and select the file
you want to open.
paraview automatically detects several of the commonly-known file
naming patterns used for indicating a file series. These include:
fooN.vtk
fooN.vtk
Nfoo.vtk
foo.vtk.N
foo_N.vtk
foo.N.vtk
N.foo.vtk
foo.vtksN
where foo could be any filename, N is a numeral sequence (with
any number of leading zeros), and vtk could be any extension.
When you open a dataset with time, either as a file series or in a file format
that natively supports time, paraview will automatically setup an
animation for you so that you can play through each of the time steps in the
dataset by using the button
on the VCRControls toolbar (Fig. 2.8).
You can change or modify this animation and
further customize it, as discussed in Chapter Section 7.
VCRControls toolbar for interacting with an animation.
paraview remembers most recently opened files (or file series).
Simply use the File > Recent Files menu. paraview also
remembers the reader type selected for files with unknown extensions or for occasions when
multiple reader choices were available.
paraview provides a command line option that can be used to open
datasets on startup.
>paraview--data=.../ParaViewData/Data/can.ex2
This is equivalent to opening a can.ex2 data file from the OpenFile dialog.
The same set of follow-up actions happen. For example, paraview will try to
locate a reader for the file, create that reader, and wait for you to hit
Apply .
To open a file series, simply replace the numbers in the file name sequence by
a . For example, to open a file series named my0.vtk, my1.vtk … myN.vtk, use my..vtk.
ParaView uses different reader implementations for different file formats. Each
of these have different properties available to you to customize how the data is
read and can vary greatly depending on the capabilities of the file format
itself or the particular reader implementation. Let’s look at some of the
properties commonly available in readers.
Array selection widget for selecting array to load from a data file.
One of the most common properties on readers is one that allows you to select
the data arrays (cell centered, point centered, or otherwise, if
applicable) to be loaded. Often times, loading only the data arrays you know you
are going to use in the visualization will save memory, as well as processing
time, since the reader does not have to read in those data arrays, and
the filters in the pipeline do not have to process them.
Did you know?
You can change paraview’s default behavior to load all available data arrays by
selecting the LoadAllVariables checkbox under
Settings/PropertiesPanelOptions/Advanced .
The user interface for selecting the arrays to load is simply a list with the names of the
arrays and a checkbox indicating whether that array is to be loaded or not
(Fig. 2.9). Icons, such as and
are often
used in this widget to give you an indication of whether the array is
cell-centered or point-centered, respectively.
If you initially de-select an array, but then as you’re setting up your visualization pipeline
realize that you need that data array, you can always go back to the
Properties page for the reader by making the reader active in the
PipelineBrowser and then changing the array selection. ParaView will
automatically re-execute any processing pipeline set up on the reader with this
new data array.
Common Errors
Remember to hit Apply (or use AutoApply ) after changing the array
selection for the change to take effect.
Sometimes the list of data arrays can get quite large, and it can
become cumbersome to find the array for which you are looking. To help
with such situations, paraview provides a mechanism to search lists. Click inside the
widget to make it get the focus. Then type CTRL + F (or
⌘ + F) to get a search widget. Now you can type in the text to
search. Matching rows will be highlighted (Fig. 2.10).
To search through large lists in paraview, you can use CTRL + F.
Did you know?
The ability to search for items in an array selection widget also applies to
other list and tree widgets in the paraview UI. Whenever
you see a widget with a large number of entries in a list, table, or tree fashion,
try using CTRL + F (or ⌘ + F).
OpenDataFile will try to determine an appropriate reader based on the file
extension, just like paraview. If no reader is determined,
None is returned. If multiple readers can open the
file, however, OpenDataFile simply picks the first reader. If you
explicitly want to create a specific reader, you can always create the reader by
its name, similar to other sources and filters.
To find out information about the reader created and the properties available on it,
you can use the help function.
>>> reader=ExodusIIReader(FileName=".../ParaViewData/Data/can.ex2")>>> help(reader)Help on ExodusIIReader in module paraview.servermanager object:class ExodusIIReader(ExodusIIReaderProxy) | The Exodus reader loads | Exodus II files and produces an unstructured grid output. | The default file extensions are .g, .e, .ex2, .ex2v2, | .exo, .gen, .exoII, .exii, .0, .00, .000, and .0000. The | file format is described fully at: | http://endo.sandia.gov/SEACAS/Documentation/exodusII.pdf. | ... | | ----------------------------------------------------------------- | Data descriptors defined here: | | AnimateVibrations | If this flag is on and HasModeShapes is also on, then | this reader will report a continuous time range [0,1] and | animate the displacements in a periodic sinusoid. If this | flag is off and HasModeShapes is on, this reader ignores | time. This flag has no effect if HasModeShapes is off. | | ApplyDisplacements | Geometric locations can include displacements. When this | option is on, the nodal positions are 'displaced' by the | standard exodus displacement vector. If displacements are | turned 'off', the user can explicitly add them by applying | a warp filter. | ...
Did you know?
The help function can be used to get information about properties available on
any source or filter instance. It not only lists the properties, but also
provides information about how they affect the pipeline module. help can
also be used on functions. For example:
>>> help(OpenDataFile)Help on function OpenDataFile in module paraview.simple:OpenDataFile(filename, \*\*extraArgs) Creates a reader to read the given file, if possible. This uses extension matching to determine the best reader possible. If a reader cannot be identified, then this returns None.
Unlike paraview, pvpython does not automatically
detect and load file series. There are two ways you can load a file series:
You can explicitly list the filenames in the
series and pass that to the OpenDataFile call.
# Create a list with the names of all the files in the file series in# correct order.>>>files=[".../Data/multicomb_0.vts",".../Data/multicomb_1.vts",".../Data/multicomb_2.vts"]>>>reader=OpenDataFile(files)
You can use globbing by inserting the wildcard * in the file name
using the utility paraview.util.Glob. This utility runs fnmatch
python package on the server’s file system, so any pattern
supported by fnmatch is supported and interpreted by this utility.
>>> importparaview.util# Create a list of names of all the files in the file series.>>> files=paraview.util.Glob(path="multicomb_*.vts",rootDir=".../Data")>>> reader=OpenDataFile(files)
Similar to paraview, if you open a time series or a file with
multiple timesteps, pvpython will automatically set up an animation
for you to play through the timesteps.
>>> files=[".../Data/multicomb_0.vts", ".../Data/multicomb_1.vts", ".../Data/multicomb_2.vts"]>>> reader=OpenDataFile(files)>>> Show()>>> Render()# Get access to the animation scene.>>> scene=GetAnimationScene()# Now you use the API on the scene when doing things such as playing# the animation, stepping through it, etc.# This will simply play through the animation once and stop. Watch# the rendered view after you hit `Enter.'>>> scene.Play()
For those properties on readers that allow you to control what to read in from
the file such as point data arrays, cell data arrays, or data blocks,
paraview uses a selection widget, as seen in
Section 2.1.6.1. Likewise, pvpython provides
an API that allows you to determine the available options and then
select/deselect them.
The name of the property that allows you to make such selections depends on the
reader itself. When in doubt, use the tracing capabilities in
paraview (Section 1.6.2) to figure it out. You can also use
help (Section 2.2).
ExodusIIReader has a PointVariables property that can be used to
select the point data arrays to load. Let’s use this as an example.
# Open an ExodusII data file.>>>reader=OpenDataFile(".../Data/can.ex2")# Alternatively, you can explicitly create the reader instance as:>>>reader=ExodusIIReader(FileName=".../Data/can.ex2")# To query/print the current status for `PointVariables' property,# we do what we would have done for any other property:>>>print(GetProperty("PointVariables"))['DISPL','VEL','ACCL']# An alternative way of doing the same is as follows:>>>print(reader.PointVariables)['DISPL','VEL','ACCL']# To set the property, simply set it to list containing the names to# enable, e.g., if we want to read only the 'DISPL' array, we do# the following:>>>SetProperties(PointVariables=['DISPL'])# Or using the alternative way for doing the same:>>>reader.PointVariables=['DISPL']# Now, the new value for PointVariables is:>>>print(reader.PointVariables)['DISPL']# To determine the array available, use:>>>print(reader.PointVariables.Available)['DISPL','VEL','ACCL']# These are the arrays available in the file.
Changing PointVariables only changes the value on the property. The reader
does not re-execute until a re-execution is requested either by calling
Render or by explicitly updating the pipeline using UpdatePipeline .
>>> reader.PointVariables=['DISPL','VEL','ACCL']# Assuming that the reader is indeed the active source, let's update# the pipeline:>>> UpdatePipeline()# Or you can use the following form if you're unsure of the active# source or just do not want to worry about it.>>> UpdatePipeline(proxy=reader)# Print the list of point arrays read in.>>> print(reader.PointData[:])[Array: ACCL, Array: DISPL, Array: GlobalNodeId, Array: PedigreeNodeId, Array: VEL]# Change the selection.>>> reader.PointVariables=['DISPL']# Print the list of point arrays read in, nothing changes!>>> print(reader.PointData[:])[Array: ACCL, Array: DISPL, Array: GlobalNodeId, Array: PedigreeNodeId, Array: VEL]# Update the pipeline.>>> UpdatePipeline()# Now the arrays read in has indeed changed as we expected.>>> print(reader.PointData[:])[Array: DISPL, Array: GlobalNodeId, Array: PedigreeNodeId]
We will cover the reader.PointData API in more details in Section 3.3.
While ParaView is often used after the simulation has generated all the data,
it is not uncommon to use ParaView to inspect data files as they are being
written out by the simulation. In such cases, the simulation may either be
modifying existing file(s) with new timesteps or creating
new files for each timestep. In such cases, you may want to refresh
ParaView to make it aware of the changes. In paraview, this can be done using
ReloadFiles .
When the reader is active, you can use the File > Reload Files menu to
request the reader to refresh. paraview will prompt you to choose whether to
reload the existing file(s) or look for new files in the file series, as shown in
Fig. 2.11. Click on Reloadexistingfile(s) , to force
the reader to re-read the files already opened. This is useful in cases
where the simulation may have modified existing file(s).
Use Findnewfiles to make the reader aware of any new files in the
file series.
The ReloadOptions dialog allows you to choose how to refresh the reader.
Similar to paraview, in pvpython, you use ReloadFiles to reload existing files, and
ExtendFilesSeries to look for new files in a file series.
# For file being modified in place per timestep>>>reader=OpenDataFile(file)...>>>ReloadFiles(reader)# For files being generated per timestep>>>reader=OpenDataFile(file)...>>>ExtendFilesSeries(reader)
To use ParaView effectively, you need to understand the ParaView data model.
ParaView uses VTK, the Visualization Toolkit, to provide the visualization
and data processing model. This chapter briefly introduces the VTK
data model used by ParaView. For more details, refer to one of the VTK books.
The most fundamental data structure in VTK is a data object. Data objects can
either be scientific datasets, such as rectilinear grids or finite elements meshes
(see below), or more abstract data structures, such as graphs or trees. These
datasets are formed from smaller building blocks: mesh (topology and geometry) and
attributes.
Even though the actual data structure used to store the mesh in memory depends
on the type of the dataset, some abstractions are common to all types. In
general, a mesh consists of vertices (points ) and
cells (elements, zones). Cells
are used to discretize a region and can have various types such as tetrahedra,
hexahedra, etc. Each cell contains a set of vertices. The mapping from cells to
vertices is called the connectivity. Note that even though it is possible to
define data elements such as faces and edges, VTK does not represent these
explicitly. Rather, they are implied by a cell’s type and by its connectivity. One
exception to this rule is the arbitrary polyhedron, which explicitly stores its
faces. Fig. 3.1 is an example mesh that consists of two cells.
The first cell is defined by vertices \((0, 1, 3, 4)\), and the second cell is
defined by vertices \((1, 2, 4, 5)\). These cells are neighbors because they share
the edge defined by the points \((1, 4)\).
A mesh is fully defined by its topology and the spatial coordinates of its
vertices. In VTK, the point coordinates may be implicit, or they may be explicitly defined by
a data array of dimensions \((number\_of\_points \times 3)\).
An attribute (or a data array or field)
defines the discrete values of a field
over the mesh. Examples of attributes include pressure, temperature, velocity,
and stress tensor. Note that VTK does not specifically define different types of
attributes. All attributes are stored as data arrays, which can have an arbitrary
number of components. ParaView makes some assumptions in regards to the number
of components. For example, a 3-component array is assumed to be an array of
vectors. Attributes can be associated with points or cells. It is also possible
to have attributes that are not associated with either.
Fig. 3.2 demonstrates the use of a point-centered
attribute. Note that the attribute is only defined on the vertices.
Interpolation is used to obtain the values everywhere else. The interpolation
functions used depend on the cell type. See the VTK documentation for details.
Point-centered attribute in a data array or field.
Fig. 3.3 demonstrates the use of a cell-centered
attribute. Note that cell-centered attributes are assumed to be constant over
each cell. Due to this property, many filters in VTK cannot be directly applied
to cell-centered attributes. It is normally required to apply a CellDatatoPointData filter. In ParaView, this filter is applied automatically, when
necessary.
A uniform rectilinear grid, or image data, defines its topology and point
coordinates implicitly (Fig. 3.4). To fully define
the mesh for an image data, VTK uses the following:
Extents - These define the minimum and maximum indices in each direction. For example, an image data of extents \((0, 9)\), \((0, 19)\), \((0, 29)\) has 10 points in the x-direction, 20 points in the y-direction, and 30 points in the z-direction. The total number of points is \(10 \times 20 \times 30\).
Origin - This is the position of a point defined with indices \((0, 0, 0)\).
Spacing - This is the distance between each point. Spacing for each direction can defined independently.
The coordinate of each point is defined as follows: \(coordinate = origin +
index \times spacing\) where \(coordinate\), \(origin\), \(index\), and \(spacing\) are vectors of
length 3.
Note that the generic VTK interface for all datasets uses a flat index. The
\((i,j,k)\) index can be converted to this flat index as follows:
\(idx\_flat = k \times (npts_x \times npts_y) + j \times nptr_x + i\).
A uniform rectilinear grid consists of cells of the same type. This type is determined by the dimensionality of the dataset (based on the extents) and can either be vertex (0D), line (1D), pixel (2D), or voxel (3D).
Due to its regular nature, image data requires less storage than other datasets.
Furthermore, many algorithms in VTK have been optimized to take advantage of
this property and are more efficient for image data.
A rectilinear grid, such as Fig. 3.5, defines its topology
implicitly and point coordinates semi-implicitly. To fully define the mesh for a
rectilinear grid, VTK uses the following:
Extents - These define the minimum and maximum indices in each direction. For example, a rectilinear grid of extents \((0, 9)\), \((0, 19)\), \((0, 29)\) has 10 points in the x-direction, 20 points in the y-direction, and 30 points in the z-direction. The total number of points is \(10 \times 20 \times 30\).
Three arrays defining coordinates in the x-, y- and z-directions - These arrays are of length \(npts_x\), \(npts_y\), and \(npts_z\). This is a significant savings in memory, as the total memory used by these arrays is \(npts_x+npts_y+npts_z\) rather than \(npts_x \times npts_y \times npts_z\).
The coordinate of each point is defined as follows:
Note that the generic VTK interface for all datasets uses a flat index. The
\((i,j,k)\) index can be converted to this flat index as follows:
\(idx\_flat = k \times (npts_x \times npts_y) + j \times nptr_x + i\).
A rectilinear grid consists of cells of the same type. This type is determined
by the dimensionality of the dataset (based on the extents) and can either be
vertex (0D), line (1D), pixel (2D), or voxel (3D).
A curvilinear grid, such as Fig. 3.6, defines its
topology implicitly and point coordinates explicitly. To fully define the mesh
for a curvilinear grid, VTK uses the following:
Extents - These define the minimum and maximum indices in each direction. For example, a curvilinear grid of extents \((0, 9)\), \((0, 19)\), \((0, 29)\) has \(10 \times 20 \times 30\) points regularly defined over a curvilinear mesh.
An array of point coordinates - This array stores the position of each vertex explicitly.
The coordinate of each point is defined as follows:
\(coordinate = coordinate\_array(idx\_flat)\).
The \((i,j,k)\) index can be converted to this flat index as follows:
\(idx\_flat = k \times (npts_x \times npts_y) + j \times npts_x + i\).
A curvilinear grid consists of cells of the same type. This type is determined
by the dimensionality of the dataset (based on the extents) and can either be
vertex (0D), line (1D), quad (2D), or hexahedron (3D).
VTK natively supports Berger-Oliger type AMR datasets,
as shown in Fig. 3.7. An AMR dataset is essentially a
collection of uniform rectilinear grids grouped under increasing refinement
ratios (decreasing spacing). VTK’s AMR dataset does not force any constraint on
whether and how these grids should overlap. However, it provides support for
masking (blanking) sub-regions of the rectilinear grids using an array of bytes.
This allows VTK to process overlapping grids with minimal artifacts. VTK can
automatically generate the masking arrays for Berger-Oliger compliant meshes.
An unstructured grid, such as Fig. 3.8, is the most
general primitive dataset type. It stores topology and point coordinates
explicitly. Even though VTK uses a memory-efficient data structure to store the
topology, an unstructured grid uses significantly more memory to represent its
mesh. Therefore, use an unstructured grid only when you cannot represent your
dataset as one of the above datasets. VTK supports a large number of cell types,
all of which can exist (heterogeneously) within one unstructured grid. The full
list of all cell types supported by VTK can be found in the file vtkCellType.h
in the VTK source code. Here is the list of cell types as of when this document was written:
VTK_EMPTY_CELL
VTK_BIQUADRATIC_TRIANGLE
VTK_VERTEX
VTK_CUBIC_LINE
VTK_POLY_VERTEX
VTK_CONVEX_POINT_SET
VTK_LINE
VTK_POLYHEDRON
VTK_POLY_LINE
VTK_PARAMETRIC_CURVE
VTK_TRIANGLE
VTK_PARAMETRIC_SURFACE
VTK_TRIANGLE_STRIP
VTK_PARAMETRIC_TRI_SURFACE
VTK_POLYGON
VTK_PARAMETRIC_QUAD_SURFACE
VTK_PIXEL
VTK_PARAMETRIC_TETRA_REGION
VTK_QUAD
VTK_PARAMETRIC_HEX_REGION
VTK_TETRA
VTK_HIGHER_ORDER_EDGE
VTK_VOXEL
VTK_HIGHER_ORDER_TRIANGLE
VTK_HEXAHEDRON
VTK_HIGHER_ORDER_QUAD
VTK_WEDGE
VTK_HIGHER_ORDER_POLYGON
VTK_PYRAMID
VTK_HIGHER_ORDER_TETRAHEDRON
VTK_PENTAGONAL_PRISM
VTK_HIGHER_ORDER_WEDGE
VTK_HEXAGONAL_PRISM
VTK_HIGHER_ORDER_PYRAMID
VTK_QUADRATIC_EDGE
VTK_HIGHER_ORDER_HEXAHEDRON
VTK_QUADRATIC_TRIANGLE
VTK_LAGRANGE_CURVE
VTK_QUADRATIC_QUAD
VTK_LAGRANGE_TRIANGLE
VTK_QUADRATIC_POLYGON
VTK_LAGRANGE_QUADRILATERAL
VTK_QUADRATIC_TETRA
VTK_LAGRANGE_TETRAHEDRON
VTK_QUADRATIC_HEXAHEDRON
VTK_LAGRANGE_HEXAHEDRON
VTK_QUADRATIC_WEDGE
VTK_LAGRANGE_WEDGE
VTK_QUADRATIC_PYRAMID
VTK_LAGRANGE_PYRAMID
VTK_BIQUADRATIC_QUAD
VTK_BEZIER_CURVE
VTK_TRIQUADRATIC_HEXAHEDRON
VTK_BEZIER_TRIANGLE
VTK_TRIQUADRATIC_PYRAMID
VTK_BEZIER_QUADRILATERAL
VTK_QUADRATIC_LINEAR_QUAD
VTK_BEZIER_TETRAHEDRON
VTK_QUADRATIC_LINEAR_WEDGE
VTK_BEZIER_HEXAHEDRON
VTK_BIQUADRATIC_QUADRATIC_WEDGE
VTK_BEZIER_WEDGE
VTK_BIQUADRATIC_QUADRATIC_HEXAHEDRON
VTK_BEZIER_PYRAMID
Many of these cell types are straightforward. For details, see the VTK
documentation.
A polydata, such as Fig. 3.9, is a specialized version of an
unstructured grid designed for efficient rendering. It consists of 0D cells
(vertices and polyvertices), 1D cells (lines and polylines), and 2D cells
(polygons and triangle strips). Certain filters that generate only these cell
types will generate a polydata. Examples include the Contour and Slice filters.
An unstructured grid, as long as it has only 2D cells supported by polydata, can
be converted to a polydata using the ExtractSurfaceFilter . A polydata can be
converted to an unstructured grid using CleantoGrid .
A table, such as Fig. 3.10, is a tabular dataset that consists of rows
and columns. All chart views have been designed to work with tables. Therefore,
all filters that can be shown within the chart views generate tables. Also,
tables can be directly loaded using various file formats such as the comma-separated
values format. Tables can be converted to other datasets as long as
they are of the right format. Filters that convert tables include TabletoPoints and TabletoStructuredGrid .
You can think of a multi-block dataset (Fig. 3.11) as a
tree of datasets where the leaf nodes are simple datasets. All of the
data types described above, except AMR, are simple datasets. Multi-block
datasets are used to group together datasets that are related. The relation
between these datasets is not necessarily defined by ParaView. A multi-block
dataset can represent an assembly of parts or a collection of meshes of
different types from a coupled simulation. Multi-block datasets can be loaded or
created within ParaView using the Group filter. Note that the leaf nodes of a
multi-block dataset do not all have to have the same attributes. If you apply a
filter that requires an attribute, it will be applied only to blocks that have
that attribute.
Multi-piece datasets, such as Fig. 3.12, are similar to
multi-block datasets in that they group together simple datasets. There is one key
difference. Multi-piece datasets group together datasets that are part of a
whole mesh - datasets of the same type and with the same attributes. This data
structure is used to collect datasets produced by a parallel simulation without
having to append the meshes together. Note that there is no way to create a
multi-piece dataset within ParaView. It can only be created by using certain readers.
Furthermore, multi-piece datasets act, for the most part, as simple datasets.
For example, it is not possible to extract individual pieces or to obtain
information about them.
In the visualization pipeline (Section 1.2),
sources, readers, and filters are all producing data. In a VTK-based pipeline,
this data is one of the types discussed. Thus, when you create a source or open
a data file in paraview and hit Apply , data is being produced.
The Information panel and the StatisticsInspector panel can be used
to inspect the characteristics of the data produced by any pipeline module.
The Information panel provides summary information about the data produced by
the active source. By default, this panel is tucked under a tab below the
Properties panel. You can toggle its visibility using View > Information.
The Information panel in paraview showing data summaries for the active source.
The Information panel shows the data information for the active source. Thus,
similar to the Properties panel, it changes when the active source is
changed (e.g., by changing the selection in the PipelineBrowser ). One way
to think of this panel is as a panel showing a summary for the data currently
produced by the active source. Remember that a newly-created pipeline
module does not produce any data until you hit Apply . Thus, valid
information for a newly-created source will be shown on this panel only after
that Apply . Similarly, if you change properties on the source and hit
Apply , this panel will
reflect any changes in data characteristics. Additionally, for temporal pipelines, this panel shows
information for the current timestep alone (except as noted). Thus, as you step
through timesteps in a temporal dataset, the information displayed
will potentially change, and the panel will reflect those changes.
Did you know?
Any text on this panel is copy-able. For example, if want to copy the
number of points value to use it as a property value on the Properties
panel, simply double-click on the number or click-and-drag to select the
number and use the common keyboard shortcut CTRL + kbd:C (or
⌘ + C) to copy that value to the clipboard. Now, you can paste it
in an input widget in paraview or any other application, such as an
editor, by using CTRL + V (or ⌘ + V) or the application-specific
shortcut for pasting text from the clipboard. The same is true for numbers shown in
lists, such as the DataRanges .
The panel itself is comprised of several groups of information. Groups may be
hidden based on the type of pipeline module or the type of data being produced.
The file Properties group is shown for readers with information about the
file that is opened. For a temporal file series, as you step through each
time step, the file name is updated to point to the name of the file in the
series that corresponds to the current time step.
The Statistics group provides a summary of the dataset produced including its
type, its number of cells and points (or rows and columns in cases of Tabular
datasets), and an estimate of the memory used by the dataset. This number only
includes the memory space needed to save the data arrays for the dataset. It does not include
the memory space used by the data structures themselves and, hence, must only be treated as an
estimate.
The DataArrays group lists all of the available point, cells, and field arrays,
as well as their types and ranges for the current time step. The Currentdatatime
field shows the time value for the current timestep as a reference. As with
other places in paraview, the icons , , and are used
to indicate cell, point, and field data arrays. Since data arrays can have multiple
components, the range for each component of the data array is shown.
Bounds shows the spatial bounds of the datasets in 3D Cartesian space. This
will be unavailable for non-geometric datasets such as tables.
For reader modules, the Time group shows the available time steps and corresponding
time values provided by the file.
For structured datasets such as uniform rectilinear grids or curvilinear grids,
the Extents group is shown that displays the structured extents and dimensions
of the datasets.
All of the summary information discussed so far provides a synopsis of the entire dataset
produced by the pipeline module, including across all ranks (which will become
clearer once we look at using ParaView for parallel data processing). In cases
of composite datasets, such as mutliblock datasets or AMR datasets, recall that
these are datasets that are comprised of other datasets. In such cases, these
are summaries over all the blocks in the composite dataset. Every so often,
you will notice that the DataArrays table lists an array with the suffix
(partial) (Figure Fig. 3.14).
Such arrays are referred to as partial arrays. Partial arrays
is a term used to refer to arrays that are present on some non-composite
blocks or leaf nodes in a composite dataset, but not all. The (partial)
suffix to indicate partial arrays is also used by paraview in other
places in the UI.
The DataArrays section on Information panel showing partial arrays. Partial arrays are arrays that present on certain blocks in a composite dataset, but not all.
While summaries over all of the datasets in the composite dataset are useful,
you may also want to look at the data information for individual blocks.
To do so, you can use the DataHierarchy group, which appears when
summarizing composite datasets. The DataHierarchy widget shows the
structure or hierarchy of the composite dataset
(Figure Fig. 3.15). The Information panel
switches to showing the summaries for the selected sub-tree.
By default, the root element will be selected. You can now select any block in
the hierarchy to view the summary limited to just that sub-tree.
The DataHierarchy section on the Information panel showing
the composite data hierarchy. Selecting a particular block or subtree in this
widget will result in the reset of the Information panel showing
summaries for that block or subtree alone.
Did you know?
Memory information shown on the Information panel and
the StatisticsInspector
should only be used as an approximate reference and does not translate
to how much memory the data produced by a particular pipeline module takes. This is due
to the following factors:
The size does not include the amount of memory needed to build the data structures to store the data arrays. While, in most cases, this is negligible compared to that of the data arrays, it can be nontrivial, especially when dealing with deeply-nested composite datasets.
Several filters such as Calculator and Shrink simply pass input data arrays through, so there’s no extra space needed for those data arrays that are shared with the input. The memory size numbers shown, however, do not take this into consideration.
If you need an overview of how much physical memory is being used by ParaView in
its current state, you can use the MemoryInspector
(Section 8).
The Information panel shows data information for the active source. If you
need a quick summary of the data produced by all the pipeline modules, you can
use the StatisticsInspector panel. It’s accessible from
Views > Statistics Inspector.
The StatisticsInspector panel in paraview showing summaries for all pipeline modules.
All of the information on this panel is also presented on the Information
panel, except GeometrySize . This corresponds to how much memory is
needed for the transformed dataset used for rendering in the active view. For example, to
render a 3D dataset as a surface in the 3D view, ParaView must extract the
surface mesh as a polydata. GeometrySize represents the memory needed for
this polydata with the same memory-size-related caveats as with the
Information panel.
When scripting with ParaView, you will often find yourself needing information
about the data. While paraview sets up filter properties and color
tables automatically using the information from the data, you
must do that explicitly when scripting.
In pvpython, for any pipeline module (sources, readers, or
filters), you can use the following ways to get information about the data
produced.
>>> fromparaview.simpleimport*>>> reader=OpenDataFile(".../ParaViewData/Data/can.ex2")# We need to update the pipeline. Otherwise, all of the data# information we get will be from before the file is actually# read and, hence, will be empty.>>> UpdatePipeline()>>> dataInfo=reader.GetDataInformation()# To get the number of cells or points in the dataset:>>> dataInfo.GetNumberOfPoints()10088>>> dataInfo.GetNumberOfCells()7152# You can always nest the call, e.g.:>>> reader.GetDataInformation().GetNumberOfPoints()10088>>> reader.GetDataInformation().GetNumberOfCells()7152# Use source.PointData or source.CellData to get information about# point data arrays and cell data arrays, respectively.# Let's print the available point data arrays.>>> reader.PointData[:][Array: ACCL, Array: DISPL, Array: GlobalNodeId, Array: PedigreeNodeId, Array: VEL]# Similarly, for cell data arrays:>>> reader.CellData[:][Array: EQPS, Array: GlobalElementId, Array: ObjectId, Array: PedigreeElementId]
PointData (and CellData ) is a map or dictionary where the keys are the
names of the arrays, and the values are objects that provide more information
about each of the arrays. In the rest of this section, anything we demonstrate on
PointData is also applicable to CellData .
# Let's get the number of available point arrays.>>>len(reader.PointData)5# Print the names for all available point arrays.>>>reader.PointData.keys()['ACCL','DISPL','GlobalNodeId','PedigreeNodeId','VEL']>>>reader.PointData.values()[Array:ACCL,Array:DISPL,Array:GlobalNodeId,Array:PedigreeNodeId,Array:VEL]# To test if a particular array is present:>>>reader.PointData.has_key("ACCL")True>>>reader.PointData.has_key("--non-existent-array--")False
From PointData (or CellData ), you can get access to an object
that provides information for each of the arrays. This object gives us
methods to get data ranges, component counts, tuple counts, etc.
# Let's get information about 'ACCL' array.>>>arrayInfo=reader.PointData["ACCL"]>>>arrayInfo.GetName()'ACCL'# To get the number of components in each tuple and the number# of tuples in the data array:>>>arrayInfo.GetNumberOfTuples()10088>>>arrayInfo.GetNumberOfComponents()3# Alternative way for doing the same:>>>reader.PointData["ACCL"].GetNumberOfTuples()10088>>>reader.PointData["ACCL"].GetNumberOfComponents()3# To get the range for a particular component, e.g. component 0:>>>reader.PointData["ACCL"].GetRange(0)(-4.965284006175352e-07,3.212448973499704e-07)# To get the range for the magnitude in cases of multi-component arrays# use -1 as the component number.>>>reader.PointData["ACCL"].GetRange(-1)(0.0,1.3329898584157294e-05)# To determine the data data type for this array:>>>fromparaviewimportvtk>>>reader.PointData["ACCL"].GetDataType()==vtk.VTK_DOUBLETrue# The paraview.vtk module provides access to these constants such as# VTK_DOUBLE, VTK_FLOAT, VTK_INT, etc.# Likewise, to test the dataset type, itself:>>>reader.GetDataInformation().GetDataSetType()== \
vtk.VTK_MULTIBLOCK_DATA_SETTrue
Here’s a sample script to iterate over all point data arrays and print their
magnitude ranges:
>>> defprint_point_data_ranges(source):... """Prints array ranges for all point arrays"""... forarrayInfoinsource.PointData:... # get the array's name... name=arrayInfo.GetName()... # get magnitude range... range=arrayInfo.GetRange(-1)... print"%s = [%.3f, %.3f]"%(name,range[0],range[1])# Let's call this function on our reader.>>> print_point_data_ranges(reader)ACCL = [0.000, 0.000]DISPL = [0.000, 0.000]GlobalNodeId = [1.000, 10088.000]PedigreeNodeId = [1.000, 10088.000]VEL = [0.000, 5000.000]
Did you know?
The example scripts in this section all demonstrated how to obtain information about the data such
as the number of points and cells, data bounds, and array ranges. However, what they
do not show is how to access the raw data itself. To see how to obtain the full data,
please see Section 7.11.
The goal of any visualization process is to produce visual representations of
the data. The visual representations are shown in modules called views.
Views provide the canvas on which to display such visual representations,
as well as to dictate how these representations are generated from the raw data.
The role of the visualization pipeline is often to transform the data so that
relevant information can be represented in these views.
Referring back to the visualization pipeline from
Section 1.2, views are sinks that take in input data
but do not produce any data output (i.e., one cannot connect other pipeline
modules such as filters to process the results in a view). However,
views often provide mechanisms to save the results as images or in other formats
including PDF, VRML, and X3D.
Different types of views provide different ways of visualizing data. These can
be broadly grouped as follows:
Rendering Views are views that render geometries or volumes in a graphical context. The RenderView is one such view. Other Render View-based views, such as SliceView and QuadView , extend the basic render view to add the ability to add mechanisms to easily inspect slices or generate orthogonal views.
Chart Views cover a wide array of graphs and plots used for visualizing non-geometric data. These include views such as line charts ( LineChartView ), bar charts ( BarChartView ), bag charts ( BagChartView ), parallel coordinates ( ParallelCoordinatesView ), etc.
Comparative Views are used to quickly generate side-by-side views for parameter study, i.e., to visualize the effects of parameter changes. Comparative variants of RenderView and several types of the ChartViews are available in ParaView.
In this chapter, we take a close look at the various views available in ParaView
and how to use these views for displaying data.
Using multiple views in paraview to generate different types of visualizations from a dataset.
With multiple types of views comes the need for creating and viewing multiple
views at the same time. In this section, we look at how you can create multiple
views and lay them out.
Did you know?
Multiple views were first supported in ParaView 3.0. Before that, all data was
shown in a single 3D render view, including line plots!
paraview shows all views in the central part of the application
window. When paraview starts up, the RenderView is created
and shown in the application window by default.
New views can be created by splitting the
view frame using the SplitView controls at the top-right corner of the
view frame. Splitting a view splits the view into two equal parts, either
vertically or horizontally, based on the button used for the split.
On splitting a view, an empty frame with buttons for all known types
of views is shown. Simply click on one of those buttons to create a new view of
a chosen type.
You can move views by clicking and dragging the title bar for the view (or
empty view frame) and dropping it on the title bar on another view (or empty
view frame). This will swap the positions of the two views.
Similar to the notion of active source, there is a notion of active
view .
Several panels, toolbars, and menus will update based on the active view. The
Display properties section on the Properties panel, for example,
reflects the display properties of the active source in the active view.
Similarly, the eyeball icons in the PipelineBrowser show the visibility
status of the pipeline module in the active view. Active view is marked in the
UI by a blue border around the view frame. Only one view can be active at any time
in the application.
Besides being able to create multiple views and laying them out in a pane,
paraview also supports placing views in multiple layouts under
separate tabs. To create new tabs, use the
button in the tab bar. You can close a tab, which will destroy all views laid out
in that tab, by clicking on the button.
To pop out an entire tab as a
separate window, use the button on the
tab bar.
The active view is always present in the active tab. Thus, if you change the
active tab, the active view will also be changed to be a view in the active tab
layout. Conversely, if the active view is changed (by using the PythonShell , for example), the active tab will automatically be updated to be the tab
that contains the active view.
Did you know?
You can make the views fullscreen by using View > Fullscreen. To return
back to the normal mode, use the Esc key.
In pvpython, one can create new views using the CreateView
function or its variants, e.g., CreateRenderView .
>>> fromparaview.simpleimport*>>> view=CreateRenderView()# Alternatively, use CreateView.>>> view=CreateView("RenderView")
When a new view is created, it is automatically made active. You can manually
make a view active by using the SetActiveView function. Several of the
functions available in pvpython will use the active view when no
view is passed as an argument to the function.
# Create a view>>>view1=CreateRenderView()# Create a second view>>>view2=CreateRenderView()# Check if view2 is the active view>>>view2==GetActiveView()True# Make view1 active>>>SetActiveView(view1)>>>view1==GetActiveView()True
When using PythonShell in paraview, if you create a new view,
it will automatically be placed in the active tab by splitting the active view.
You can manually control the layout and placement of views from Python too, using
the layout API.
In Python, each tab corresponds to a layout.
# To get exisiting tabs/layouts>>>layouts=GetLayouts()>>>print(layouts){('ViewLayout1','264'):<paraview.servermanager.ViewLayoutobjectat0x2e5b7d0>}# To get layout corresponding to a particular view>>>print(GetLayout(view))<paraview.servermanager.ViewLayoutobjectat0x2e5b7d0># If view is not specified, active view is used>>>print(GetLayout())<paraview.servermanager.ViewLayoutobjectat0x2e5b7d0># To create a new tab>>>new_layout=servermanager.misc.ViewLayout(registrationGroup="layouts")# To split the cell containing the view, either horizontally or vertically>>>view=GetActiveView()>>>layout=GetLayout(view)>>>locationId=layout.SplitViewVertical(view=view,fraction=0.5)# fraction is optional, if not specified the frame is split evenly.# To assign a view to a particular cell.>>>view2=CreateRenderView()>>>layout.AssignView(locationId,view2)
Just like parameters on pipeline modules, such as
readers and filters, views provide parameters that can be used for customizing
the visualization such as changing the background color for rendering views and
adding title texts for chart views. These parameters are referred to as ViewProperties and are accessible from the Properties panel in paraview.
Similar to properties on pipeline modules like sources and readers, view
properties are accessible from the Properties panel. These
are grouped under the View section. When the active view is changed, the
Properties panel updates to show the view properties for the active view.
Unlike pipeline modules, however, when you change the view properties, they
affect the visualization immediately, without use of the Apply
button.
Did you know?
It may seem odd that View and Display properties on the
Properties panel don’t need to be Apply -ed to take effect, while
properties on pipeline modules like sources, readers and filter require you to
hit the Apply button.
To understand the reasoning behind that, we need to understand why the
Apply action is needed in the first place. Generally, executing a data
processing filter or reader is time consuming on large datasets. If the pipeline
module keeps on executing as you are changing the parameter, the user experience
will quickly deteriorate, since the pipeline will keep on executing with
intermediate (and potentially invalid) property values. To avoid this, we have
the Apply action. This way, you can set up the pipeline properties to your
liking and then trigger the potentially time consuming execution.
Since the visualization process in general focuses on reducing data to
generate visual representations, the rendering (broadly speaking) is less time-
intensive than the actual data processing. Thus, changing properties that affect
rendering are not as compute-intensive as transforming the data itself. For example,
changing the color on a surface mesh is not as expensive as generating the mesh
in the first place. Hence, the need to Apply such properties becomes less
relevant. At the same time, when changing display properties such as opacity,
you may want to see the result as you change the property to decide on the final
value. Hence, it is desirable to see the updates immediately.
Of course, you can always enable AutoApply to have the same immediate
update behavior for all properties on the Properties panel.
In pvpython, once you have access to the view, you can directly change view
properties on the view object. There are several ways to get access to the view
object.
# 1. Save reference when a view is created>>>view=CreateView("RenderView")# 2. Get reference to the active view.>>>view=GetActiveView()
The properties available on the view will change based on the type of the view.
You can use the help function to discover available properties.
>>> view=CreateRenderView()>>> help(view) Help on RenderView in module paraview.servermanager object:class RenderView(Proxy) | View proxy for a 3D interactive render | view. | | ---------------------------------------------------------------------- | Data descriptors defined here: | | CenterAxesVisibility | Toggle the visibility of the axes showing the center of | rotation in the scene. | | CenterOfRotation | Center of rotation for the interactor. | ...# Once you have a reference to the view, you can then get/set the properties.# Get the current value>>> print(view.CenterAxesVisibility)1# Change the value>>> view.CenterAxesVisibility=0
Display properties refers to available parameters that control how data from a
pipeline module is displayed in a view, e.g., choosing to view the output mesh as a
wireframe, coloring the mesh using a data attribute, and selecting which attributes
to plot in chart view. A set of display properties is associated with a
particular pipeline module and view. Thus, if the data output from a source is
shown in two views, there will be two sets of display properties used to control
the appearance of the data in each of the two views.
Display properties are accessible from the Display section on the
Properties panel. When the active source or active view changes, this
section updates to show the display properties for the active source in the
active view, if available. If the active source produces data that cannot be
shown (or has never been shown) in the view, then the Display properties
section may be empty.
Similar to view properties, display property changes are immediately applied,
without requiring the use of the Apply button.
To access display properties in pvpython, you can use SetDisplayProperties and GetDisplayProperty methods.
# Using SetDisplayProperties/GetDisplayProperties to access the display# properties for the active source in the active view.>>>print(GetDisplayProperties("Opacity"))1.0>>>SetDisplayProperties(Opacity=0.5)
Alternatively, you
can get access to the display properties object using GetDisplayProperties
and then changing properties directly on the object.
# Get display properties object for the active source in the active view.>>>disp=GetDisplayProperties()# You can also save the object returned by Show.>>>disp=Show()# Now, you can directly access the properties.>>>print(disp.Opacity)0.5>>>disp.Opacity=0.75
As always, you can use the help method to discover available properties on a
display object.
>>> disp=Show()>>> help(disp)>>> help(a)Help on GeometryRepresentation in module paraview.servermanager object:class GeometryRepresentation(SourceProxy) | ParaView`s default representation for showing any type of | dataset in the render view. | | Method resolution order: | GeometryRepresentation | SourceProxy | Proxy | __builtin__.object | | ---------------------------------------------------------------------- | Data descriptors defined here: | | ... | | CenterStickyAxes | Keep the sticky axes centered in the view window. | | ColorArrayName | Set the array name to color by. Set it to empty string | to use solid color. | | ColorAttributeType | ...
RenderView is the most commonly used view in ParaView. It is used to render
geometries and volumes in a 3D scene. This is the view that you typically think
of when referring to 3D visualization. The view relies on techniques to map data
to graphics primitives such as triangles, polygons, and voxels, and it renders
them in a scene.
Most of the scientific datasets discussed in Section 3.1
are comprised of meshes. These meshes can be mapped to graphics primitives using
several of the established visualization techniques. (E.g., you can compute the
outer surface of these meshes and then render that surface as filled polygons, you can
just render the edges, or you can render the data as a nebulous blob to get a better
understanding of the internal structure in the dataset.) Plugins, like
SurfaceLIC , can provide additional ways of rendering data using advanced
techniques that provide more insight into the data.
If the dataset doesn’t represent a mesh, e.g., a table
(Section 3.1.9), you cannot directly show that data in
this view. However, in such cases, it may be possible to construct a mesh by
mapping columns in the table to positions to construct a point cloud, for
example.
paraview using RenderView to generate 3D visualizations from a dataset.
RenderView uses data processing techniques to map raw data to graphics
primitives, which can then be rendered in a 3D scene. These mapping techniques
can be classified as follows:
Surface rendering methods provide general rendering by rendering a surface mesh for the dataset. For polygonal datasets (Section 3.1.8), this is simply the raw data. In cases of other datasets including structured (Section 3.1.3, Section 3.1.4, Section 3.1.5) and unstructured (Section 3.1.7) grids, this implies extracting a surface mesh for all external faces in the dataset and then rendering that mesh. The surface mesh itself can then be rendered as a filled surface or as a wireframe simply showing the edges, etc.
Slice rendering is available for uniform rectilinear grid datasets (Section 3.1.3) where the visualization is generated by simply rendering an orthogonal slice through the dataset. The slice position and alignment can be selected using the display properties.
Volume rendering generates rendering by tracing a ray through the dataset and accumulating intensities based on the color and opacity transfer functions set.
Each of these techniques are referred to as
representations. When
available, you can change the representation type from the display properties on the
Properties panel or using the RepresentationToolbar .
Unless you changed the default setting, a new RenderView will be created
when paraview starts up or connects to a new server. To create a
RenderView in paraview, split or close a view, and select the
RenderView button. You can also convert a view to a Render View (or any other
type) by right-clicking on the view’s title bar and picking from the ConvertTo sub-menu. It simply closes the chosen view and creates a selected view type
in its place.
You can use the PipelineBrowser to control the visibility of datasets
produced by pipeline modules in this view. The eyeball icons reflect the
visibility state. Clicking on the eyeball icon will toggle the visibility state.
If no eyeball icon is shown, it implies that the pipeline module doesn’t produce
a data type that can be directly shown in the active view, e.g., if the module
produced a table, then when RenderView is active, there will not be any
eyeball icon next to that module.
You can interact with the Render View to move the camera in the scene for
exploring the visualization and setting up optimal viewing angles.
Each of the three mouse buttons, combined with keyboard modifier keys
(CTRL or ⌘ , and ⇧ ), move the camera differently.
The interaction mode can be changed from the Camera tab in the Settings
dialog, which is accessible from Tools > Settings (or ParaView > Preferences
on macOS).
There are six interaction modes available in ParaView:
Pan for translating the camera in the view plane.
Zoom for zooming in or out of the center of the view.
Roll for rolling the camera.
Rotate for rotating the camera around the center of rotation.
Zoom To Mouse for zooming in or out of the projected point under the mouse position.
Multi Rotate for allowing azimuth and elevation rotations by dragging from the middle of the view and rolls by dragging from the edges.
Rotate Skybox for rotating the environment skybox. Useful when using Environment Lighting and PBR shader.
The default interactions options are as follows:
Modifier
Left Button
Middle Button
Right Button
Rotate
Pan
Zoom
⇧
Roll
Rotate
Pan
CTRL or ⌘
Rotate Skybox
Rotate
Zoom To Mouse
Usually in ParaView, you are interacting with a 3D scene. However, there are cases when
you are working with a 2D dataset such as a slice plane or a 2D image. In such
cases, paraview provides a separate set of interaction options
suitable for 2D interactions. You can toggle between the default 3D interaction
options and 2D interaction options by clicking the 2D or 3D button in
the view toolbar. The default interaction options for 2D interactions are as
follows:
Modifier
Left Button
Middle Button
Right Button
Pan
Roll
Zoom
⇧
Zoom
Zoom
Zoom To Mouse
CTRL or ⌘
Roll
Pan
Rotate
By default, ParaView will determine whether your data is 2D or 3D when
loading the data and will set the interaction mode accordingly. This
behavior can be changed in the Settings dialog by changing the
DefaultInteractionMode setting under the RenderView tab.
The default setting is “Automatic, based on the first time step”, but
the setting can be changed to “Always 2D” or “Always 3D” in case you
wish to force the interaction mode.
Several of the view properties in RenderView control the annotations shown
in the view (Fig. 4.3).
The Properties panel showing view properties for RenderView .
AxesGrid refers to an annotation axis rendered around all
datasets in the view (Fig. 4.4). You use
the checkbox next to the EditAxisGrid button to show or hide
this annotation. To control the annotation formatting, labels, etc.,
click on the EditAxesGrid... button. The AxesGrid is
described in Chapter Section 11.
AxesGrid is used to annotate data bounds in RenderView .
The Center axes refers to axes rendered in the scene positioned as the
center of rotation, i.e., the location is space around which the camera revolves
during Rotate camera interaction.
CenterAxesVisibility controls the visibility of the center axes.
The Orientation axes is the widget shown at the lower-left corner by
default, which is used to get a sense for the orientation of the scene. The properties
grouped under the OrientationAxes group allow you to toggle the visibility and
the interactivity of this widget. When interactivity is enabled, you can click and
drag this widget to the location of your choosing in the scene.
You can also change the Background used for this view. You can either set it as a
Single color or as a Gradient comprised of two colors, or you can select an
Image (or texture) to use as the background.
There are two advanced properties you may wish to set: hidden line removal
and camera parallel projection. The HiddenLineRemoval option
can be enabled to hide lines that would be occluded by a solid object
when drawing objects in a Wireframe representation.
If you want to render your data using parallel projection instead of
the default perspective projection you can check the
CameraParallelProjection checkbox.
One of the first (and probably the most often used) display properties is
Representation . Representation allows you to pick one of the
mapping modes. The options available depend on the data type, as well as
the plugins loaded. While all display properties are accessible from the
advanced view for the Properties panel, certain properties may be
shown/hidden from the default view based on the chosen representation type.
Different renderings generated by rendering data produced by the Wavelet source as outline, points, slice, surface, surface with edges, and volume.
The Outline representation can be used to render an outline for the
dataset. This is arguably the fastest way of rendering the dataset since only
the bounding box is rendered. Scalar coloring options, i.e., selecting an array
with which to color, has no effect on this representation type. You can still,
however, change the SolidColor to use as well as the Opacity . To change
the color, select SolidColor in the combo-box under Coloring , and then
click Edit to pick the color to use. To change the opacity, simply change
the Opacity slider. 0 implies total transparency and, hence, invisiblity, while 1
implies totally opacity.
Did you know?
Rendering translucent data generally adds computational
costs to the rendering process. Thus, when rendering large datasets, you may
want to leave changing opacities to anything less than 1 to the very end,
after having set up the visualization. In doing so, you avoid translucent geometries
during exploration, but use them for generating images or screenshots for
presentations and publications.
Points , Surface , SurfaceWithEdges , and Wireframe rely on
extracting the surface mesh from the dataset and then rendering that either as a
collection of points, as solid surface, as solid surface with cell boundaries
highlighted, or as a wireframe of cell boundaries only. FeatureEdges
is a subset of Wireframe consisting of prominent edges on the surface such
as edges between cells that form a sharp angle or edges with only one adjacent cell.
For these representations, you can either set a single solid color to use,
as with Outline , or select a data array to use for scalar coloring (also
known as pseudocoloring).
Two other representations are available for most datasets. 3DGlyphs draws
a copy of a 3D geometry (e.g., arrow, cone, or sphere, etc.), or glyph, at a subset
of points in the dataset. These glyphs can be set to a single color or
pseudocolored by a data array. The PointGaussian representation is similar,
but instead of drawing 3D geometry at every point, it draws a 2D image sprite
that may have transparency. The image drawn can be one of several predefined
image sprites such as GaussianBlur , Sphere , Black-edgedcircle ,
Plaincirlce , Triangle , or Squareoutline , or a custom sprite
can be defined with custom GLSL shader code.
Did you know?
For visualizations that feature 3D glyphs, it is typically much faster to
use the 3DGlyph representation rather than the Glyph filter. This is because
the glyph representation draws the same geometry at many different locations (a graphics
technique called geometry instancing) while the Glyph filter makes many copies of the
same source geometry and renders the resulting mesh in its entirety. Generating all the glyphs and
rendering them takes potentially a lot of memory and is typically slower to render, so
you should use the 3DGlyph representation when possible.
Next, we will cover each of the property groups available under Display
properties. Several of these are marked as advanced. Accordingly, you may need to
either toggle the panel to show advanced properties using the
button or search for it by name using the search
box.
Display properties under Coloring allow you to set
how the dataset is
colored. To select a single solid color to use to fill the surface or color the
wireframe or points, select SolidColor in the combo-box, and then
click Edit . That will pop up the standard color chooser dialog from which you
can pick a color to use.
If instead you want to pseudocolor using an attribute array
available on the dataset, select that array name from the combo-box. For
multi-component arrays, you can pick a particular component or Magnitude to
use for scalar coloring. ParaView will automatically setup a color transfer
function it will use to map the data array to colors. The default range for the
transfer function is set up based on the TransferFunctionResetMode general
setting in the Settings dialog when the transfer function is first created.
If another dataset is later colored by a data array with the same name, the range
of the transfer function will be updated according to the AutomaticRescaleRangeMode
property in the ColorMapEditor . To reset the transfer function range to the
range of the data array in the selected dataset, you can use the Rescale
button. Remember that, despite the fact that you can set the scalar array with
which to color when rendering as Outline , the outline itself continues to use
the specified solid color.
ScalarColoring properties are only relevant when you have selected a data
array with which to pseudocolor. The MapScalars checkbox affects whether a color
transfer function should be used (Fig. 4.6).
If unchecked, and the data array can directly
be interpreted as colors, then those colors are used directly. If not, the color
transfer function will be used. A data array can be interpreted as colors if, and
only if, it is an unsigned char, float, or double array with two, three, or four
components. If the data array is unsigned char, the color values are defined between
0 and 255 while if the data array is float or double, the color values are expected
to be between 0 and 1. InterpolateScalarsBeforeMapping controls how color
interpolation happens across rendered polygons. If
on, scalars will be interpolated within polygons, and color mapping will occur
on a per-pixel basis. If off, color mapping occurs at polygon points, and colors
are interpolated, which is generally less accurate. Refer to the Kitware blog
[PatMarion] for a detailed explanation of this option.
The MapScalars property can be used to avoid using a transfer function and directly interpreting the array values as colors, if possible.
The PolarAxes checkbox toggles polar axes shown around the data.
Many parameters can be accessed via an Editbutton alongside it.
The parameters include angles, tick range, labels, logarithmic mode,
ellipse ratio and more.
Styling properties include Opacity (useful when rendering translucent
geometries), PointSize (used to control size of points rendered with using
Points representation), and LineWidth (used to control the thickness
of lines when rendering as Wireframe or that of the edges when rendering as
SurfaceWithEdges .
Lighting properties affect the shading for rendered surfaces.
Interpolation allows you to pick between Flat and Gouraud
shading. Specular , together with SpecularColor and SpecularPower , affects the shininess of the surface. Set this to a non-zero value to
render shiny, metallic surfaces.
Common Errors
Specular highlights can lead to misinterpretation of scalar values when
using scalar coloring, since the color shown on the shiny part of the surface
will not correspond to any color on the color transfer function. Hence, it is
generally advisable to use specular highlights on surfaces colored with a single
solid color and not on those using scalar coloring (or
pseudocoloring).
EdgeStyling allows you to set the EdgeColor with which to color the edges
when using SurfaceWithEdges representation.
BackfaceStyling provides advanced controls to fine-tune the rendering by
controlling front and back faces. A front face is any mesh face facing the
camera, while a back face is the one facing away from the camera. By choosing to
CullFrontface or CullBackface , or by selecting a specific representation
type to use for the backface, you can customize your visualizations.
Transforming properties can be used to transform the rendered data in the
scene without affecting the raw data itself. Thus, if you apply filters on the
data source, it will indeed be working with the untransformed data. To transform
the data itself, you should use the Transform filter.
Several properties are available under the Miscellaneous group. Uncheck the Pickable
option if you want the dataset to be ignored when making selections. If the
dataset has a texture coordinates array, you can apply a texture to the dataset
surface using the Texture combo-box. Choose Load to load a texture or
apply a previously loaded texture listed in the combo-box. If your dataset
doesn’t have texture coordinates, you can create them by applying one of
TextureMaptoCylinder , TextureMaptoSphere , or TextureMapToPlane filters, or using the filters Calculator or ProgrammableFilter .
The Triangulate option is useful for rendering objects with
non-convex polygons. It comes with some additional processing cost for
converting polygons to triangles, so it should be used only when necessary.
A dataset made of quadratic tetra hedra displayed with 1, 2, and 3 levels of nonlinear subdivision.
The NonlinearSubdivisionLevel is used when rendering datasets with higher-
order elements. Use this to set the subdivision level for triangulating higher
order elements. The higher the value, the smoother the edges. This comes at the
cost of more triangles and, hence, potentially, increased rendering time.
The BlockColorsDistinctValues sets the number
of unique colors to use when coloring multi-block datasets by block ID. Finally,
UseDataPartitions controls whether data is redistributed when it is
rendered translucently. When off (default value), data is repartitioned by the
compositing algorithm prior to rendering. This is typically an expensive
operation that slows down rendering. When this option is on, the existing data
partitions are used, and the cost of data restribution is avoided. However, if
the partitions are not sortable in back-to-front order, rendering artifacts may
occur.
VolumeRendering options are available if the data can be volume rendered.
You can pick a specific type of VolumeRenderingMode , although the
default ( Smart ) should work in most cases, since it attempts to pick a
volume rendering mode suitable for your data and graphics setup. To enable
gradient-based shading, check Shade , if available.
Slicing properties are available when the Slice representation type is
present. These allow you to pick the orthogonal slice plane orientation and
slice offset using SliceDirection and the Slice slider.
You use CreateRenderView or CreateView functions to create a new
instance of a render view.
>>> fromparaview.simpleimport*>>> view=CreateRenderView()# Alternatively, use CreateView.>>> view=CreateView("RenderView")
noindent
You use Show and Hide to show or hide data produced by a pipeline
module in the view.
>>> source=Sphere()>>> view=CreateRenderView()# Show active source in active view.>>> Show()# Or specify source and view explicitly.>>> Show(source,view)# Hide source in active view.>>> Hide(source)
Since pvpython is designed for scripting and batch processing,
it has limited support for direct interaction with the view.
To interact with a scene, invoke the Interact function in Python.
Interact()
More often, you will programmatically change the camera as follows:
# Get camera from the active view, if possible.>>>camera=GetActiveCamera()# or, get the camera from a specific render view.>>>camera=view.GetActiveCamera()# Now, you can use methods on camera to move it around the scene.# Divide the camera's distance from the focal point by the given dolly value.# Use a value greater than one to dolly-in toward the focal point, and use a# value less than one to dolly-out away from the focal point.>>>camera.Dolly(10)# Set the roll angle of the camera about the direction of projection.>>>camera.Roll(30)# Rotate the camera about the view up vector centered at the focal point. Note# that the view up vector is whatever was set via SetViewUp, and is not# necessarily perpendicular to the direction of projection. The result is a# horizontal rotation of the camera.>>>camera.Azimuth(30)# Rotate the focal point about the view up vector, using the camera's position# as the center of rotation. Note that the view up vector is whatever was set# via SetViewUp, and is not necessarily perpendicular to the direction of# projection. The result is a horizontal rotation of the scene.>>>camera.Yaw(10)# Rotate the camera about the cross product of the negative of the direction# of projection and the view up vector, using the focal point as the center# of rotation. The result is a vertical rotation of the scene.>>>camera.Elevation(10)# Rotate the focal point about the cross product of the view up vector and the# direction of projection, using the camera's position as the center of# rotation. The result is a vertical rotation of the camera.>>>camera.Pitch(10)
Alternatively, you can explicitly set the camera position, focal point, view up,
etc,. to explicitly place the camera in the scene.
>>> camera.SetFocalPoint(0,0,0)>>> camera.SetPosition(0,0,-10)>>> camera.SetViewUp(0,1,0)>>> camera.SetViewAngle(30)>>> camera.SetParallelProjection(False)# If ParallelProjection is set to True, then you'll need# to specify parallel scalar as well i.e. the height of the viewport in# world-coordinate distances. The default is 1. Note that the `scale'# parameter works as an `inverse scale' where larger numbers produce smaller# images. This method has no effect in perspective projection mode.>>> camera.SetParallelScale(1)
In pvpython, view properties are directly accessible on the view
object returned by CreateRenderView or GetActiveView .
Once you get access to the view properties objects, you can then set properties
on it similar to properties on pipeline modules such as sources, filters, and
readers.
>>> view=GetActiveView()# Set center axis visibility>>> view.CenterAxesVisibility=0# Or you can use this variant to set the property on the active view.>>> SetViewProperties(CenterAxesVisibility=0)# Another way of doing the same>>> SetViewProperties(view,CenterAxesVisibility=0)# Similarly, you can change orientation axes related properties>>> view.OrientationAxesVisibility=0>>> view.OrientationAxesLabelColor=(1,1,1)
Similar to view properties, display properties are accessible from the display
properties object or using the SetDisplayProperties function.
>>> displayProperties=GetDisplayProperties(source,view)# Both source and view are optional. If not specified, the active source# and active view will be used.# Now one can change properties on this object>>> displayProperties.Representation="Outline"# Or use the SetDisplayProperties API.>>> SetDisplayProperties(source,view,Representation=Outline)# Here too, source and view are optional and when not specified,# active source and active view will be used.
You can always use the help function to get information about available
properties on a display properties object.
paraview using LineChartView to plot data values probed along a line through the dataset using PlotOverLine filter.
LineChartView can be used to plot data as a line plot representing
changes in dependent variables against an independent variable. Using display
properties, you can also show scatter plots in this view. This view and other
charting views in ParaView follow a similar design, where you pick attribute
arrays to plot using display properties, and they are plotted in the view. How
those values get plotted depends on the type of the view: LineChartView
draws a line connecting sample points, BarChartView renders bars at each
sample point, etc.
One of the most common ways of showing a line plot is to apply the PlotOverLine filter to any dataset. This will probe the dataset along the probe line
specified. You then plot the sampled values in the LineChartView .
Alternatively, if you have a tabular dataset (i.e. vtkTable ), then you can
directly show the data in this view.
Did you know?
You can plot any arbitrary dataset, even those not producing vtkTable outputs,
by using the PlotData filter. Remember, however, that for
extremely large datasets, while RenderView may use parallel rendering
strategies to improve performance and reduce memory requirements, chart views
rarely, if ever, support such parallel strategies.
LineChartView plots data arrays. For any dataset being shown in the view,
you first select which data array is to be treated as the independent variable
and plotted along the x-axis. Then, you select which arrays to plot along the
Y-axis. You can select multiple of these and setup properties for each of the
series so they are rendered with different colors and line styles. Since data
arrays in VTK datasets are associated with cells or points, and the two are not
directly comparable to one another, you can only pick arrays associated with
one type of attribute at any time.
Similar to creating RenderView , you can split the viewport or convert
an existing view to LineChartView . LineChartView will also be
automatically created if you apply a filter that needs this view, e.g., the
PlotOverLine filter.
Did you know?
If you generate lengthy data for the LineChartView , the default variables
that are selected may be slow to adjust. You can change paraview’s default
behavior to initially load no variables at all by selecting the
LoadNoChartVariables checkbox under
Settings/General/PropertiesPanelOptions .
Interactions with the chart view result in changing the plotted axes ranges.
You can left-click and drag to pan, i.e., change the origin. To change the range
on either of the axes, you can right-click and drag vertically and/or horizontally
to change the scale on the vertical axes and/or horizontal axes, respectively.
You can also explicitly specify the axes range using view properties.
The view properties for LineChartView are grouped as properties that
affect the view and those that affect each of the potential four axes.
To set a title, use ChartTitle . Title text properties such as font, size,
style, and alignment with respect to the chart can be set under ChartTitleProperties . To toggle the visibility of the legend, use ShowLegend . While
you cannot interactively place the legend in this view, you can use LegendLocation to place it at one of the corners.
There are four axes possible in this view: left, bottom, top, and right. The top
and right axes are shown only when some series is set to use those. (We will
cover this in the Display properties subsection.) For each of the axes,
you can set a title (e.g., LeftAxisTitle , BottomAxisTitle , etc.)
and adjust the title font properties. You can turn on a grid with a customizable
color by checking the ShowLeftAxisGrid , for example.
Next, you can customize the axes ranges. You can always simply interact with the
mouse to set the axes ranges. To precisely set the range, check the
AxisUseCustomRange for the appropriate axis, e.g., BottomAxisUseCustomRange for fixing the bottom axis range, and then specify the data values to
use for the min and the max.
The labels on the axes are, by default, automatically determined to avoid visual
clutter. By default, the axis labels are arranged on a linear scale, but by
enabling the AxisLogScale option you can use log scaling instead. In
addition, you can override the default labelling strategy for any of the axes
separately and, instead, specify the locations to label explicitly. This can be
done by checking AxisUseCustomLabels for a particular axis, e.g.,
BottomAxisUseCustomLabels . When checked, a list widget will be shown
where you can manually add values at which labels will be placed.
For generating log plots, simply check the corresponding AxisUseLogScale ,
e.g., LeftAxisUseLogScale to use log scale for Y-axis
(Fig. 4.10). Note that log
scale should only be used for an axis with a non-zero positive range, since the log of a
number less than or equal to 0 is undefined.
Differences between line charts when using log scale for the Y-axis.
Display properties allow you to setup which series or data arrays are plotted in
this view. You start by picking the AttributeType . Select the attribute
type that has the arrays of interest. For example, if you are plotting arrays
associated with points, then you should pick PointData .) Arrays with
different associations cannot be plotted together. You may need to apply filters
such as CellDatatoPointData or PointDatatoCellData to convert
arrays between different associations for that.
Properties under XAxisParameters allow you to select the independent
variable plotted on the X axis by choosing the XArrayName . If none of the
arrays are appropriate, you can choose to use the element index in the array as
the X axis by checking UseIndexforXAxis .
SeriesParameters control series or data arrays plotted on the Y-axis. All
available data arrays are lists in the table widget that allows you to
check/uncheck a series to plot in the first column. The second column in the
table shows the associated color used to plot that series. You can double-click
the color swatch to change the color to use. By default, ParaView will try to
pick a palette of discrete colors. The third column shows the label to use for
that series in the legend. By default, it is set to be the same as the array
name. You can double-click to change the name to your choice, e.g., to add units.
Other series parameters include LineThickness , LineStyle , and MarkerStyle . To change any of these, highlight a row in the SeriesParameters
widget, and then change the associated parameter to affect the highlighted
series. You can change properties for multiple series and can select multiple of
them by using the CTRL (or ⌘) and ⇧ keys.
Using ChartAxes , you can change which axes on which a series is shown. The
default is Bottom-Left , but you can change it to be Bottom-Right ,
Top-Left , or Top-Right to accommodate series with widely different
ranges in the same plot.
The principles involved in accessing LineChartView from
pvpython are similar to those with RenderView . You work with
the view properties and display properties objects to change views and display
properties, respectively. The thing that changes is the set of available
properties.
The following script demonstrates the typical usage:
>>> fromparaview.simpleimport*# Create a data source to probe into.>>> Wavelet()<paraview.servermanager.Wavelet object at 0x1156fd810># We update the source so that when we create PlotOverLine filter# it has input data available to determine good defaults. Otherwise,# we will have to manually set up the defaults.>>> UpdatePipeline()# Now, create the PlotOverLine filter. It will be initialized using# defaults based on the input data.>>> PlotOverLine()<paraview.servermanager.PlotOverLine object at 0x1156fd490># Show the result.>>> Show()<paraview.servermanager.XYChartRepresentation object at 0x1160a6a10># This will automatically create a new Line Chart View if the# the active view is no a Line Chart View since PlotOverLine# filter indicates it as the preferred view. You can also explicitly# create it by using CreateView() function.# Display the result.>>> Render()# Access display properties object.>>> dp=GetDisplayProperties()>>> print(dp.SeriesVisibility)['arc_length', '0', 'RTData', '1']# This is list with key-value pairs where the first item is the name# of the series, then its visibility and so on.# To toggle visibility, change this list e.g.>>> dp.SeriesVisibility=['arc_length','1','RTData','1']# Same is true for other series parameters including series color,# line thickness etc.# For series color, the value consists of 3 values: red, green, and blue# color components.>>> print(dp.SeriesColor)['arc_length', '0', '0', '0', 'RTData', '0.89', '0.1', '0.11']# For series labels, value is the label to use.>>> print(dp.SeriesLabel)['arc_length', 'arc_length', 'RTData', 'RTData']# e.g. to change RTData's legend label, we can do something as follows:>>> dp.SeriesLabel[3]='RTData -- new label'# Access view properties object.>>> view=GetActiveView()# or>>> view=GetViewProperties()# To change titles>>> view.ChartTitle="My Title">>> view.BottomAxisTitle="X Axis">>> view.LeftAxisTitle="Y Axis"
paraview using BarChartView to plot the histogram for a dataset using the Histogram filter.
BarChartView is very similar to LineChartView when it comes to
creating the view, view properties, and display properties. One difference is
that, instead of rendering lines for each series, this view renders bars. In addition,
under the display properties, the SeriesParameters like LineStyle and
LineThickness are not available, since they are not applicable to bars.
paraview using BoxChartView to plot the box chart for a dataset using the ComputeQuartiles filter.
Box plot is a standard method for graphically depicting groups of statistical
data based on their quartiles. A box plot is represented by a box with the
following properties: the bottom of the rectangle corresponds to the first
quartile, a horizontal line inside the rectangle indicates the median and the
top of the rectangle corresponds to the third quartile. The maximum and minimum
values are depicted using vertical lines that extend from the top and the bottom
of the rectangle.
In ParaView, the BoxChartView can be used to display such box plots through
the ComputeQuartiles filter which computes the statistical data needed by
the view to draw the box plots.
paraview using PlotMatrixView to generate a scatter plot matrix to understand correlations between pairs of variables.
PlotMatrixView is a chart view that renders a scatter plot matrix. It
allows you to spot patterns in the small scatter plots, change focus to those
plots of interest, and perform basic selection. The principle is that, for all
selected arrays or series to be plotted, the view generates a scatter plot for
each pair. You can activate a particular scatter plot, in which case the active
plot is re-drawn at a bigger scale to make it easier to inspect.
Additionally, the view shows a histogram for each plotted variable or series.
The view properties allow you to set colors to use for active plot, histograms,
etc., while the display properties allow you to pick which series are plotted.
You can click on any of the plots (except the histograms) in the matrix to make
it active. Once actived, the active plot will show that plot. You can then
interact with the active plot exactly like LineChartView or BarChartView for panning and zoom.
View properties on this view allow you to pick styling parameters for the
rendering ranging from title ( ChartTitle ) to axis colors ( ActivePlotAxisColor , ActivePlotGridColor ). You can also control the visibility
of the histrogram plots, the active plot, the axes labels, the grids, and so on.
Similar to LineChartView , you select the AttributeType and then the
arrays to plot. Since, in a scatter plot matrix, the order in which the selected
series are rendered can make it easier to understand correlations, you can
change the order by clicking and dragging the rows in the SeriesParameters
table.
paraview using ParallelCoordinatesView to plot correlations between columns in a table.
Like PlotMatrixView , ParallelCoordinatesView is also used to
visualize correlations between data arrays.
One of the main features of this view is the ability to select specific data in order to analyse
the factors influencing the data. e.g., with a table of three variables, one being the “output” variable
the other two being the potential factor influencing the first, selecting only the output will enable you
to see if none, one, or both of the factors are actually influencing the output.
High “S” data point are influenced more by low “Ks” than high “Q”
paraview using SpreadSheetView to plot raw data values for the can.ex2 dataset.
SpreadSheetView is used to inspect raw data values in a tabular form.
Unlike most other views, this view is primarily intended to be used in the
paraview user interface and, hence, is not available in
pvpython.
To use this view, simply create this view and show the dataset produced by any
pipeline module in it by using the PipelineBrowser . SpreadSheetView
can only show one dataset at a time. Therefore, showing a new dataset will
automatically hide the previously shown dataset.
The view’s toolbar provides quick access to several of this view’s capabilities.
Use the Showing widget on the view toolbar to view as well as to change the
dataset being shown. The Attribute field allows you to pick which types of
elements to show, e.g., CellData , PointData , FieldData , etc.
Precision can be utilized to change the precision used when displaying floating
point numbers.
The button enables you to select columns to
show. Click on the button to get a popup menu in which you check/uncheck the
columns to show/hide.
If showing CellData , the button, when
checked, enables you to see the point ids that form each of the cells.
Section 6.1 discusses how selections can be made in
views to select elements of interest. Use the
button to make the view show only selected elements. Now, as you make selections
in other views, this SpreadSheetView will update to only show the values
of the selected elements (as long as the dataset selected in are indeed being shown
in the view).
Did you know?
Some filters and readers produce vtkTable, and they are automatically displayed
in a spreadsheet view. Thus, one can very easily read the contents of a .csv file
with ParaView.
SliceView can be used to show orthogonal slices from datasets.
SliceView is special type of RenderView that can be used to view
orthogonal slices from any dataset. Any dataset shown in the view will be sliced
in axis-aligned slices based on the locations specified on the view. The
slice locations along the three orthogonal axis planes can be specified by using
the frame decoration around the view window.
Since this view is a type of RenderView , the camera interactions are same as
that of RenderView . Additionally, you can interact with the frame
decoration to manipulate slice locations along the three axis planes.
Double-click the left mouse button in the region between the axis border and the view to add a new slice.
You can click-and-drag a marker to move the slice location.
To remove a slice, double-click with the left mouse button on the marker corresponding to that slice.
To toggle visibility of the slice, you can right-click on the marker.
# To create a slice view in use:>>>view=CreateView("MultiSlice")# Use properties on view to set/get the slice offsets.>>>view.XSliceValues=[-10,0,10]>>>print(view.XSliceValues)[-10,0,10]# Similar to XSliceValues, you have YSliceValues and ZSliceValues.>>>view.YSliceValues=[0]>>>view.ZSliceValues=[]
Some Python libraries, such as matplotlib, are widely used for making
publication-quality plots of data. The PythonView provides a way
to display plots made in a Python script right
within paraview.
The PythonView has a single property, a Python script that
generates the image to be displayed in the viewport. All the Python
bindings for ParaView and VTK that are available in the Python
scripting module are available from within this script, making it
possible to plot any array from just about any dataset that can be
loaded into ParaView. The Python script for the view is evaluated in a
unique Python environment so that global variables defined in the
script do not clobber global variables in other Python scripts (either
in other instances of the PythonView or in the Python
interpreter). This environment is reset each time the script is
evaluated, so data cannot be saved between evaluations.
The PythonView requires that the Python script where the
plotting occurs define two functions. In the first function, you
request which arrays you would like to transfer to the client for
rendering. At present, all rendering in this view takes place on the
client, even in client-server mode. These arrays can be point data,
cell data, field data, and table row data. This function runs only on
data-server processes. It provides access to the underlying data
object on the server so that you can query any aspect of the data
using the Python-wrapped parts of VTK and ParaView.
The second function is where you put Python plotting or rendering
commands. This function runs only on the ParaView client. It has
access to the complete data object gathered from the data server
nodes, but only has access to the arrays requested in the first function. This
function will typically set up objects from a plotting library,
convert data from VTK to a form that can be passed to the plotting
library, plot the data, and convert the plot to an image
(a vtkImageData object) that can be displayed in the viewport.
All the rendering in the PythonView occurs in the client, so the
client must get the data from the server. Because the dataset residing
on the ParaView server may be large, transferring all the data to the
client may not be possible or practical. For that reason, we have
provided a mechanism to select which data arrays in a data object on
the server to transfer to the client. The overall structure of the
data object, however, (including cell connectivity, point positions,
and hierarchical block structure) is always transferred to the client.
By default, no data arrays are selected for transfer from the server.
The Python script for the view must define a function called
setup_data(view) . The view argument is the VTK object for the PythonView . The current datasets loaded into ParaView may be accessed
through the view object.
paraview using PythonView with matplotlib to display a scatterplot of momentum magnitude versus density (upper right) and a histogram of density (lower right) in the bluntfin.vts dataset.
Here’s an example of this function that was used to generate the image
in Fig. 4.18:
defsetup_data(view):# Iterate over visible data objectsforiinrange(view.GetNumberOfVisibleDataObjects()):# You need to use GetVisibleDataObjectForSetup(i)# in setup_data to access the data object.dataObject=view.GetVisibleDataObjectForSetup(i)# The data object has the same data type and structure# as the data object that sits on the server. You can# query the size of the data, for instance, or do anything# else you can do through the Python wrapping.print('Memory size: {0} kilobytes'.format(dataObject.GetActualMemorySize()))# Clean up from previous calls here. We want to unset# any of the arrays requested in previous calls to this function.view.DisableAllAttributeArrays()# By default, no arrays will be passed to the client.# You need to explicitly request the arrays you want.# Here, we'll request the Density point data arrayview.SetAttributeArrayStatus(i,vtkDataObject.POINT,"Density",1)view.SetAttributeArrayStatus(i,vtkDataObject.POINT,"Momentum",1)# Other attribute arrays can be set similarlyview.SetAttributeArrayStatus(i,vtkDataObject.FIELD,"fieldData",1)
The vtkPythonView class passed in as the view argument to
setup_data(view) defines several methods useful for specifying which
data arrays to copy:
GetNumberOfVisibleDataObjects() -
This returns the number of visible data objects in the view. If an object
is not visible, it should not show up in the rendering, so all the
methods provided by the view deal only with visible objects.
GetVisibleDataObjectForSetup(visibleObjectIndex) -
This returns the visibleObjectIndex'th visible data object in
the view. (The data object will have an open eye next to it in the
pipeline browser.)
GetNumberOfAttributeArrays(visibleObjectIndex,attributeType) -
This returns the number of attribute arrays for
the visibleObjectIndex'th visible object and the
given attributeType
(e.g., vtkDataObject.POINT , vtkDataObject.CELL , etc.).
GetAttributeArrayName(visibleObjectIndex,attributeType,arrayIndex) -
This returns the name of the array of the given attribute type at the
given array index for the visibleObjectIndex'th object.
SetAttributeArrayStatus(visibleObjectIndex,vtkDataObject.POINT,"Density",1) -
This sets the array status of an attribute array. The first argument is
the visible object index, the second object is the attribute
association of the array, the third argument is the name of the
array, and the last argument specifies if the array is to be copied
(1) or not (0).
GetAttributeArrayStatus(visibleObjectIndex,vtkDataObject.POINT,"Density") -
This retrieves the array status for the object with the given visible
index with a given attribute association (second argument) and a name
(last argument).
EnableAllAttributeArrays() -
This sets all arrays to be copied.
DisableAllAttributeArrays() -
This sets all arrays to not be copied.
The methods GetNumberOfVisibleDataObjects() ,
GetVisibleDataObjectForSetup(...) , GetNumberOfAttributeArrays(...) ,
and GetAttributeArrayName(...) are all convenient methods for
obtaining information about visible data objects in the view that
could otherwise be accessed with existing view and representation
methods. The last four methods are valid only from within
the setup_data(view) function.
After the setup_data(view) function has been called, ParaView
will transfer the data object and selected arrays to the client. When
that is done, it will call the render(view,width,height)
function you have defined in your script.
The view argument to the render(view,width,height)
function is the vtkPythonView object on the
client. The width and height arguments are the width and
height of the viewport, respectively. The render(view,width,height) function uses the data available through the view, along with
the width and height, to generate a vtkImageData object that will
be displayed in the viewport. This vtkImageData object must be
returned from the render(view,width,height) function. If no
vtkImageData is returned, the viewport will be black. If the size of the
image does not match the size of the viewport, the image will be
stretched to fit the viewport.
Putting it all together, here is a simple example that generates a
solid red image to display in the viewport.
This example does not produce an interesting visualization, but serves
as a minimal example of how the render(view,width,height)
function should be implemented. Typically, we expect that the Python
plotting library you use has some utilities to expose the generated
plot image pixel data. You need to copy that pixel data to
the vtkImageData object returned by the render(view,width,height)
function. Exactly how you do this is up to you, but ParaView
comes with some utilities to make this task easier for matplotlib.
The PythonView comes with a Python module,
called python_view , that has some utility functions you can
use. To import it, use:
fromparaviewimportpython_view
This module has a function, called matplotlib_figure(view,width,height) , that returns a matplotlib.figure.Figure given width
and height arguments. This figure can be used with matplotlib
plotting commands to plot data as in the following:
defrender(view,width,height):figure=python_view.matplotlib_figure(width,height)ax=figure.add_subplot(1,1,1)ax.minorticks_on()ax.set_title('Plot title')ax.set_xlabel('X label')ax.set_ylabel('Y label')# Process only the first visible object in the pipeline browserdataObject=view.GetVisibleDataObjectForRendering(0)x=dataObject.GetPointData().GetArray('X')# Convert VTK data array to numpy array for plottingfromparaview.numpy_supportimportvtk_to_numpynp_x=vtk_to_numpy(x)ax.hist(np_x,bins=10)returnpython_view.figure_to_image(figure)
This definition of the render(view,width,height) function
creates a histogram of a point data array named X from the first
visible object in the pipeline browser. Note the conversion
function, python_view.figure_to_image(figure) , in the last line.
This converts the matplotlib Figure object created
with python_view.matplotlib_figure(width,height) into a
vtkImageData object suitable for display in the viewport.
ComparativeViews , including RenderView(Comparative) , LineChartView(Comparative) , and BarChartView(Comparative) , are used
for generating comparative visualization from parameter studies. These views
are covered in Section 4 of the Reference Manual.
ParaView supports immersive data visualization in virtual reality (VR) with
head-mounted displays (HMDs). VR can be used to view the scene in the current
Render View and interact with it. This environment provides enhanced perception
of depth and more intuitive manipulation of 3D objects by creating the sensation
of the user being physically present inside of the scene.
VR support in ParaView is provided through the XRInterface plugin (previously
called OpenVR plugin). To load this plugin, open the PluginManager via
Tools > Manage Plugins…. Click on XRInterface, then on the button
LoadSelected. This will open the XRInterface panel.
By default, the XRInterface plugin is already enabled in ParaViewWindows binaries. Simply launch ParaView
with a VR runtime such as SteamVR on your machine to easily experience VR with
ParaView.
Otherwise, the plugin needs to be enabled before building ParaView
(PARAVIEW_PLUGIN_ENABLE_XRInterface CMake option). At least one between the OpenVR
or OpenXR modules should be enabled as well (VTK_MODULE_ENABLE_VTK_RenderingOpenVR
or VTK_MODULE_ENABLE_VTK_RenderingOpenXR, respectively), with the corresponding
external dependencies available.
By default, the XRInterface panel appears on the right upon loading the plugin.
To open it manually, search for the corresponding checkbox in the main menu via
View > XRInterface.
Once the XRInterface plugin is loaded and an HMD connected, click on the
button SendtoXR to start rendering in VR. Other options are available in
the plugin panel:
UseMultiSamples — This checkbox indicates whether multisampled framebuffers
are used. Using multisamples can reduce flickering but currently does not work
with volume rendering.
BaseStationVisibility — This checkbox indicates whether the base stations
models are displayed in VR.
DesiredXRRuntime — This drop down list indicates whether to use OpenVR or
OpenXR when both are available.
SendtoXR - This button launches the VR mode using the selected runtime.
AttachtoCurrentView — This button allows VR-only elements to appear in
the current Render View, such as cropping planes or avatars. This option is mainly
useful in Collaboration mode for desktop users when an HMD is not available.
ShowXRView - This button opens a window showing a stabilized view of what the VR
headset is showing, which is useful to produce screenshots or videos.
ExportLocationsasaView — This button exports saved locations as .vtp
files in a folder called pv-view. This option is meant to be used for Mineview.
ExportLocationsasSkyboxes — This button exports saved locations as skyboxes
in a folder called pv-skybox. This generates six .jpg images (right, left, up,
down, back and front) producing a skybox that can then be used outside of
VR as well.
CropThickness — This value indicates the thickness of thick cropping planes.
EditableField — This field indicates which cell scalar array can be edited
in VR.
FieldValues — This field contains the values available when editing cell
scalar values in VR. Values should be separated by commas. They will appear in
the XR menu for assignment to specific cells and for the array specified in
EditableField. See Section 4.14.3.1 for more details.
On top of head tracking to reproduce the user physical movements for navigation,
the controllers can be used to interact with the data through actions such as scaling,
picking, etc.
The controls mapping for different controllers is detailed in Section 4.14.4.
Trigger actions are assigned to the right trigger by default and include grabbing,
picking, probing, interactive clipping and adding points to sources (such as a polyline
source). The current action can be chosen via the XR menu (see Section 4.14.3).
Adding points to a source — Press the right trigger to place a point at
the tip of the right controller. Only valid when the active source allows placing
points, such as a polyline source.
In the XR View, pressing the menu button opens a dedicated menu floating in the
3D scene in front of the user. This menu is composed of elements found outside of
VR, as well as components only available in the XR mode.
Pipeline Browser — This is the same pipeline browser present in ParaView.
The visibility for each item in the pipeline can be modified by pointing the
navigation ray on the eye icon and pressing the right trigger.
Panels — The first panels mostly correspond to the ones found in ParaView:
Properties, Information, and Display. The last one, Widgets,
contains several VR specific options described below in Section 4.14.3.1.
Quick access options — The lower left portion of the menu provides convenient
options for interacting with the XR View. These options are detailed below in
Section 4.14.3.2.
This panel provides options for widgets and advanced properties of the XR View:
CroppingWidgets — This section provides tools to crop data in real time.
Cropping planes can be moved by placing the right controller on them and grabbing
them with the right trigger. More than one plane can be added to the scene.
AddCropPlane — This button adds a cropping plane to the scene.
AddThickCrop — This button adds a thick cropping plane to the scene.
RemoveAllCropPlanes — This button removes all cropping planes from
the scene.
SnapCropPlanes — This checkbox indicates whether the cropping planes
should snap to the coordinates axes.
OtherWidgets — This section currently contains options for the measuring tool.
DistanceWidget — This button adds a measuring tool to the scene.
Press the right trigger once to place the starting point where the right
controller is located, then press a second time with the controller at the
desired location to place the second point. Four values are displayed next
to the tool: distance and X, Y, Z difference between both points.
RemoveDistanceWidget — This button removes the measuring tool from the scene.
AnimationIcons — These buttons are used to animate temporal data sets
or to move between timesteps.
ViewUp — This drop down list indicates which axis and direction point
upwards from the top of the HMD. This is useful when datasets or skyboxes are
oriented differently from the default.
ShowFloor — This checkbox indicates whether to display the floor
as a white plane.
ScaleFactor — This drop down list indicates the scaling factor of the scene.
A higher value results in all objects appearing larger.
MotionFactor — This drop down list indicates the movement speed when using
the joysticks. A higher value corresponds to a higher speed.
LoadCameraPose — This drop down list contains slots with user defined
positions in the scene. Click on one of the numbered slots to load the associated
saved position. Note that it is also possible to move sequentially between saved
positions by pressing the left trigger.
SaveCameraPose — This drop down list contains slots to save the current
position of the user in the scene. Click on one of the numbered slots to save
the current position in that slot.
BringCollaboratorsHere — This button moves all collaborators to your
current location. Only applicable in Collaboration mode.
AdjustScalarValue — This section offers options to modify the cell scalar
values of the dataset.
FieldValue — This drop down list indicates which value to assign to a cell.
The values appearing in the list are those defined in the XRInterface panel
with the FieldValues box for the specified EditableField.
AssignValue — This button assigns the value selected with FieldValue
to the currently selected cell. Cells can be selected with the Probe trigger action.
The lower left part of the menu contains the following convenient options:
RightTrigger — This drop down list indicates which action is mapped to
the right trigger outside of the menu, such as picking, probing, etc. See
Section 4.14.2.1 for the list of available actions.
Resetallpositions — This button resets the position of all objects within
the scene.
InteractiveRay — This checkbox indicates whether the ray changes color
when pointing at an object to signal a collision.
NavigationPanel — This checkbox indicates whether to display a tooltip
above the left controller with information on its spatial position in world coordinates.
This section details the button mappings used in ParaView for different types
of controllers. The controls names are those used throughout the VR section.
Visualization can be characterized as a process of transforming raw data
produced from experiments or simulations until it takes a form in which it can be
interpreted and analysed. The visualization pipeline introduced in
Section 1.2 formalizes this concept as a data flow
paradigm where a pipeline is set up of sources, filters, and sinks
(collectively called pipeline modules or algorithms). Data flows
through this pipeline, being transformed at each node until it is in a form where
it can be consumed by the sinks. In previous chapters, we saw how to ingest data
into ParaView (Section 2) and how to display it in
views (Section 4). If the data ingested into ParaView
already has all the relevant attribute data, and it is in the form that can be directly
represented in one the existing views, then that is all you would need.
The true power of the visualization process, however, comes from leveraging the
various visualization techniques such as slicing, contouring, clipping, etc.,
which are available as filters. In this chapter, we look at constructing
pipelines to transform data using such filters.
In ParaView, filters are pipeline modules or algorithms that have inputs and
outputs. They take in data on their inputs and produce transformed data or
results on their outputs. A filter can have multiple input and output ports.
The number of input and output ports on a filter is fixed. Each input port accepts
input data for a specific purpose or role within the filter. (E.g., the
ResampleWithDataset filter has two input ports. The one called Input
is the input port through which the dataset providing the attributes to
interpolate is ingested. The other, called Source , is the input port
through which the dataset used as the mesh on which to re-sample is accepted.)
A filter is a pipeline module with inputs and outputs.
Data enters a filter through the inputs. The filter transforms the data and
produces the resulting data on its outputs. A filter can have one or more input
and output ports. Each input port can optionally accept multiple input
connections.
An input port itself can optionally accept multiple input connections, e.g., the
AppendDatasets filter, which appends multiple datasets to create a single
dataset only has one input port (named Input ). However, that port can accept
multiple connections for each of the datasets to be appended . Filters define
whether a particular input port can accept one or many input connections.
Similar to readers, the properties on the filter allow you to control the
filtering algorithm. The properties available depend on the filter itself.
All available filters in paraview are listed under the Filters
menu. These are organized in various categories. To create a filter to transform
the data produced by a source or a reader, you select the source in the PipelineBrowser
to make it active, and then click on the corresponding menu item in the
Filters menu. If a menu item is disabled, it implies that the active source
does not produce data that can be transformed by this filter.
Did you know?
If a menu item in the Filters menu is disabled, it implies that the active
source(s) is not producing data of the expected type or the characteristics needed
by the filter. On Windows and Linux machines, if you hover over the disabled
menu item, the status bar will show the reason why the filter is not available.
When you create a filter, the active source is connected to the first input port
of the filter. Filters like AppendDatasets can take multiple input
connections on that input port. In such a case, to pass multiple pipeline
modules as connections on a single input port of a filter, select all the
relevant pipeline modules in the PipelineBrowser . You can select multiple
items by using the CTRL (or ⌘) and ⇧ key
modifiers. When multiple pipeline modules are selected, only the filters that
accept multiple connections on their input ports will be enabled in the
Filters menu.
The PipelineBrowser showing a pipeline with multiple input
connections. The AppendDatasets filter has two input connections on its
only input port, Sphere0 and Cone0 .
Most filters have just one input port. Hence, as soon as you click on the filter
name in the Filters menu, it will create a new filter instance and that
will show up in the PipelineBrowser . Certain filters, such as ResampleWithDataset , have multiple inputs that must be set up before the filter can be
created. In such a case, when you click on the filter name, the ChangeInputDialog will pop up, as seen in Fig. 5.3.
This dialog allows you to select the pipeline modules to be
connected to each of the input ports. The active source(s) is connected by
default to the first input port. You are free to change those as well.
The ChangeInputDialog is shown to allow you to pick inputs for
each of the input ports for a filter with multiple input ports. To use this
dialog, first select the InputPort you want to edit on the left side, and
select the pipeline module(s) that are to be connected to this input port.
Repeat the step for the other input port(s). If an input port can accept
multiple input connections, you can select multiple modules, just like in the
PipelineBrowser .
paraview allows you to change the inputs to a filter after the
filter has been created. To change inputs to a filter, right-click on the filter
in the PipelineBrowser to get the context menu, and then select ChangeInput... . This will pop up the same ChangeInputDialog as when creating a
filter with multiple input ports. You can use this dialog to set new inputs
for this filter.
The context menu in the PipelineBrowser showing the option to
change inputs for a filter.
Did you know?
While the Filters menu is a handy way to create new filters, with the long list
of filters available in ParaView, manually finding a particular filter in this
menu can be very challenging. To make it easier, ParaView incorporates a quick
launch mechanism. When you want to create a new filter (or a source), simply type
CTRL + Space or Alt + Space. This will pop up
the quick-launch dialog. Now, start typing the name of the filter you want. As
you type, the dialog will update to show the filters and sources that match the
typed text. You can use the arrow keys to navigate and use the Enter key
to create the selected filter (or source). Press ⇧ while pressing Enter
to quickly apply the filter on creation, equivalent to creating the filter and then
clicking the Apply button. Note that filters may be disabled,
as was the case in the Filters menu but by default the selected item
will be the first enabled filter.
You can use Esc to clear the text you have typed so far. Hit the
Esc a second time, and the dialog will close without creating any new
filter.
Similar to paraview, the filter will use the active source(s) as
the input. Additionally, you can explicitly specify the input in the function
arguments.
To setup multiple input connections, you can specify the connections as follows:
>>> sphere=Sphere()>>> cone=Cone()# Simply pass the sources as a list to the constructor function.>>> appendDatasets=AppendDatasets(Input=[sphere,cone])>>> print(appendDatasets.Input)[<paraview.servermanager.Sphere object at 0x6d75f90>, <paraview.servermanager.Cone object at 0x6d75c50>]
Setting up connections to multiple input ports is similar to the multiple input
connections, except that you need to ensure that you name the input ports properly.
Changing inputs in Python is as simple as setting any other property on the
filter.
# For filter with single input connection>>>shrink.Input=cone# for filters with multiple input connects>>>appendDatasets.Input=[reader,cone]# to add a new input.>>>appendDatasets.Input.append(sphere)# to change multiple ports>>>resampleWithDataSet.Input=wavelet2>>>resampleWithDataSet.Source=cone
Filters provide properties that you can change to control the processing
algorithm employed by the filter. Changing and viewing properties on filters is
the same as with any other pipeline module, including readers and sources.
You can view and change these properties, when available, using the
Properties panel.
Section 1 covers how to effectively use the
Properties panel. Since this panel only shows the properties present on the
active source , you must ensure that the filter
you are interested in is active. To make the filter active, use the PipelineBrowser to click on the filter and select it.
With pvpython, the available properties are accessible as properties
on the filter object, and you can get or set their values by name (similar to
changing the input connections
(Section 5.3.3)).
# You can save the object reference when it's created.>>>shrink=Shrink()# Or you can get access to the active source.>>>Shrink()# <-- this will make the Shrink the active source.>>>shrink=GetActiveSource()# To figure out available properties, you can always use help.>>>help(shrink)HelponShrinkinmoduleparaview.servermanagerobject:classShrink(SourceProxy)|TheShrinkfilter|causestheindividualcellsofadatasettobreakapart|fromeachotherbymovingeachcell\'s points toward the|centroidofthecell.(Thecentroidofacellisthe|averagepositionofitspoints.)Thisfilteroperateson|anytypeofdatasetandproducesunstructuredgrid|output.|----------------------------------------------------------------------|Datadescriptorsdefinedhere:||Input|ThispropertyspecifiestheinputtotheShrink|filter.||ShrinkFactor|Thevalueofthispropertydetermineshowfarthepoints|willmove.Avalueof0positionsthepointsatthecentroidofthe|cell;avalueof1leavesthemattheiroriginal|positions.....# To get the current value of a property:>>>sf=shrink.ShrinkFactor>>>printsf0.5# To set the value>>>shrink.ShrinkFactor=0.75
In the rest of this chapter, we will discuss some of the commonly used filters
in detail. They are grouped under categories based on the type of operation that they
perform.
These filters are used for extracting subsets from an input dataset. How this
subset is defined and how it is extracted depends on the type of the filter.
Clip is used to clip any dataset using either an implicit function (such as
a plane, sphere, or a box) or using values of a scalar data array in the input
dataset. A scalar array is a point or cell attribute array with a single
component. Clipping involves iterating over all cells in the input dataset and then
removing those cells that are considered outside of the space defined by
the implicit function or that have an attribute values less than the selected value.
For cells that straddle the clipping surface, these are clipped to pass
through the part of the cell that is truly inside the specified implicit
function (or greater than the scalar value).
This filter converts any dataset into an unstructured grid
(Section 3.1.7) or a multi-block of
unstructured grids (Section 3.1.10) in the case of composite
datasets.
Comparison between results produced by the Clip filter with
CrinkleClip unchecked (left) and checked (right) when clipping with an
implicit plane. The image on the left also shows the 3D widget used to
interactivly place the implicit plane for the clipping operation.
To create the Clip filter, you can use the Filters > Common or
the Filters > Alphabetical menu. This filter is also accessible from the
Common filters toolbar. You can click the button to create
this filter.
The Common filters toolbar in paraview for quick
access to the commonly used filters.
On the Properties panel, you will see the available properties for this
filter. One of the first things that you should select is the ClipType .
ClipType is used to specify the type of implicit function to use for the
clipping operations. The available options include Plane , Box ,
Sphere , and Scalar . Selecting any one of these options will update
the panel to show properties that are used to define the implicit function, e.g.,
the Origin and the Normal for the Plane or the Center and
the Radius for the Sphere . If you select Scalar , the panel will let
you pick the data array and the value with which to clip. Remember, cells with the
data value greater than or equal to the selected value are considered in
and are passed through the filter.
Did you know?
When clipping with implicit functions, ParaView renders widgets in the active
view that you can use to interactively control the implicit function, called
3Dwidgets . As you interact with the 3D widget, the panel will update to
reflect the current values. The 3D widget is considered as an aid and not as a part
of the actual visualization scene. Thus, if you change the active source and the
Properties panel navigates away from this filter, the 3D widget will
automatically be hidden.
The InsideOut option can be used to invert the behavior of this filter.
Basically, it flips the notion of what is considered inside and outside of the given
clipping space.
Check CrinkleClip if you don’t want this filter to truly clip cells on the
boundary, but want to preserve the input cell structure and to pass the entire cell on through the
boundary (Fig. 5.5).
This option is not available when clipping by Scalar .
This following script demonstrates various aspects of using the Clip filter
in pvpython.
# Create the Clip filter.>>>clip=Clip(Input=...)# Specify a 'ClipType' to use.>>>clip.ClipType='Plane'# You can also use the SetProperties API instead.>>>SetProperties(clip,ClipType='Plane')>>>print(clip.GetProperty('ClipType').GetAvailable())['Plane','Box','Sphere','Scalar']# To set the plane origin and normal>>>clip.ClipType.Origin=[0,0,0]>>>clip.ClipType.Normal=[1,0,0]# If you want to change to Sphere and set center and# radius, you can do the following.>>>clip.ClipType='Sphere'>>>clip.ClipType.Center=[0,0,0]>>>clip.ClipType.Radius=12# Using SetProperties API, the same looks like>>>SetProperties(clip,ClipType='Sphere')>>>SetProperties(clip.ClipType,Center=[0,0,0],Radius=12)# To set Crinkle clipping.>>>clip.Crinkleclip=1# For clipping with scalar, you pick the scalar array# and then the value as follows:>>>clip.ClipType='Scalar'>>>clip.Scalars=('POINTS','Temp')>>>clip.Value=100
# As always, to get the list of available properties on# the clip filter, use help()>>>help(clip)HelponClipinmoduleparaview.servermanagerobject:classClip(SourceProxy)|TheClipfilter|cutsawayaportionoftheinputdatasetusingan|implicitplane.Thisfilteroperatesonalltypesofdata|sets,anditreturnsunstructuredgriddataon|output.||----------------------------------------------------------------------|Datadescriptorsdefinedhere:||ClipType|Thispropertyspecifiestheparametersoftheclip|function(animplicitplane)usedtoclipthedataset.||Crinkleclip|Thisparametercontrolswhethertoextractentirecells|inthegivenregionorclipthosecellssoalloftheoutputonestay|onlyinsidethatregion.||Input|ThispropertyspecifiesthedatasetonwhichtheClip|filterwilloperate.||InsideOut|Ifthispropertyissetto0,theclipfilterwill|returnthatportionofthedatasetthatlieswithintheclipfunction.|Ifsetto1,theportionsofthedatasetthatlieoutsidetheclip|functionwillbereturnedinstead....# To get help on a specific implicit function type, make it the active# ClipType and then use help()>>>clip.ClipType='Plane'>>>help(clip.ClipType)HelponPlaneinmoduleparaview.servermanagerobject:classPlane(Proxy)...
Common Errors
It is very easy to forget that clipping a structured dataset such as image
data can dramatically increase the memory requirements, since this filter will
convert the structured dataset into an unstructured grid due to the nature of
the clipping operation itself. For structured dataset, think about using
Slice or ExtractSubset filters instead, whenever appropriate. Those
are not entirely identical operations, but they are often sufficient.
Comparison between results produced by the Slice filter
when slicing image data with an implicit plane with different options.
The lower-left image shows the output produced by the Clip filter
when clipping with the same implicit function, for contrast.
The Slice filter slices through the input dataset with an implicit function
such as a plane, a sphere, or a box. Since this filter returns data elements along
the implicit function boundary, this is a dimensionality reducing filter (except
when crinkle slicing is enabled), i.e., if
the input dataset has 3D elements like tetrahedrons or hexahedrons, the output
will have 2D elements, line triangles, and quads, if any. While slicing through a
dataset with 2D elements, the result will be lines.
The properties available on this filter, as well as the way of setting this
filter up, is very similar to the Clip filter with a few notable
differences. What remains similar is the set up of the implicit function –
you have similar choices: Plane , Box , Sphere , and Cylinder , as well as the
option to toggle Crinkleslice (i.e., to avoid cutting through cells,
pass complete cells from the input dataset that intersects the implicit function).
What is different includes the lack of slicing by Scalar (for that, you
can use the Contour filter) and a new option, Triangulatetheslice .
Fig. 5.7
shows the difference in the generated meshes when various slice properties are
changed.
The Slice filter is more versatile than the Slice representation. First,
the Slice representation is available for image datasets only, whereas the
Slice filter can be used on any type of 3D dataset. Second, the representation
extracts a subset of the image consisting of a 2D slice oriented in the XY,
YZ, or XZ planes at the image voxel locations while the plane used by the filter
can be placed arbitrarily. Third, since the Slice representation always
shows a flat object and lighting may interfere with interpretation of data values
on the slice, lighting is not applied to the Slice representation. Lighting
is applied, however, to results from the Slice filter. Lastly, the Slice
representation may be faster than the filter to update and scrub through different
slices because it does not need to compute the intersection of a plane with cells
in the dataset.
In paraview, this filter can be created using the
button on the Common filters toolbar, besides the
Filters menu.
The Properties panel for the ExtractSubset filter showing all
available properties (including the advanced properties).
For structured datasets such as
image datasets (Section 3.1.3), rectilinear grids
(Section 3.1.4), and
curvilinear grids (Section 3.1.5), ExtractSubset filter can be used to extract a region of interest or a subgrid. The
region to extract is specified using structured coordinates, i.e., the
\(i\), \(j\), \(k\) values. Whenever possible, this filter should be preferred over
Clip or Slice for structured datasets, since it preserves the input
data type. Besides extracting a subset, this filter can also be used to resample
the dataset to a coarser resolution by specifying the sample rate along each of
the structured dimensions.
This is one of the filters available on the Common filters toolbar
To specify the region of interest, use the VOI property. The values are
specified as min and max values for each of the structured dimensions (\(i\), \(j\),
\(k\),) in each row. SampleRateI , SampleRateJ ,
and SampleRateK specify the sub-sampling rate. Set it to a value greater than one to sub-sample.
IncludeBoundary is used to determine if the boundary slab should be
included in the extracted result, if the sub-sampling rate along that dimension
is greater than 1, and the boundary slab would otherwise have been skipped.
Results from using the Threshold filter on the iron_protein.vtk dataset from ParaView data.
The Threshold filter extracts cells of the input dataset with scalar
values lying within the specified range, depending on the selected threshold method.
This filter operates on either point-centered or cell-centered data.
Any type of dataset can be used as input. The filter produces an unstructured grid output.
When thresholding with cell data, all cells that have scalars within the
specified range will be passed through the filter. When thresholding with point
data, cells with all points with scalar values within the range are passed
through if AllScalars is checked; otherwise, cells with any point
that passes the thresholding criteria are passed through.
This filter is represented as on the Common filters toolbar.
After selecting the Scalars with which to threshold from the combo-box, the
LowerThreshold and UpperThreshold values can be modified to specify the
range. If the range shown by the sliders is not sufficient, it is also possible
to manually type the values in the input boxes. The values are deliberately not
clamped to the current data range.
The threshold method can also be selected using the ThresholdMethod combo box:
Between: Extracts cells with scalar values between the LowerThreshold
and UpperThreshold.
BelowLowerThreshold: Extracts cells with scalar values smaller than the
LowerThreshold.
AboveUpperThreshold: Extracts cells with scalar values larger than the
UpperThreshold.
# Create the filter. If Input is not specified, the active source will be# used as the input.>>>threshold=Threshold(Input=...)# Here's how to select a scalar array.>>>threshold.Scalars=("POINTS","scalars")# The value is a tuple where the first value is the association: either "POINTS"# or "CELLS", and the second value is the name of the selected array.>>>print(threshold.Scalars)['POINTS','scalars']>>>print(threshold.Scalars.GetArrayName())'scalars'>>>print(threshold.Scalars.GetAssociation())'POINTS'# Different threshold methods are available and are set using one of the following:>>>threshold.ThresholdMethod="Between"# Uses both lower and upper values>>>threshold.ThresholdMethod="Below Lower Threshold"# Uses only lower value>>>threshold.ThresholdMethod="Above Upper Threshold"# Uses only upper value# The adequate threshold values are then specified as:>>>threshold.LowerThreshold=63.75>>>threshold.UpperThreshold=252.45
To determine the types of arrays available in the input dataset, and their
ranges, refer to the discussion on data information in
Section 3.3.
The IsoVolume filter is similar to Threshold in that you use this to
create an output dataset from an input where the cells that satisfy the
specified range are scalar values. In fact, the filter is identical to
Threshold when the cell data scalars are selected. For point data scalars,
however, this filter acts similar to the Clip filters when clipping with
scalars, in that cells are clipped along the iso-surface formed by the scalar range.
ExtractSelection is a general-purpose filter to extract selected elements
from a dataset. There are several ways of making selections in ParaView. Once
you have made the selection, this filter allows you to extract the selected
elements as a new dataset for further processing. We will cover this filter in
more detail when looking at selections in ParaView in
Section 6.6.
The Transform can be used to arbitrarily translate, rotate, and scale a
dataset. The transformation is applied by
scaling the dataset, rotating it, and then translating it
based on the values specified.
As this is a geometric manipulation filter, this filter does not affect
connectivity in the input dataset. While it tries to preserve the input dataset
type, whenever possible, there are cases when the transformed dataset can no
longer be represented in the same data type as the input. For example, with
image data (Section 3.1.3) and
rectilinear grids (Section 3.1.4) that are
transformed by rotation, the output dataset can be non-axis aligned and, hence,
cannot be represented as either data types. In such cases, the dataset is
converted to a structured, or curvilinear, grid
(Section 3.1.5). Since curvilinear grids are
not as compact as the other two, the need to store the results in a more general
data type implies a considerable increase in the memory footprint.
You can create a new Transform from the Filters > Alphabetical menu.
Once created, you can set the transform as the translation, rotation, and scale
to use utilizing the Properties panel. Similar to Clip , this filter also
supports using a 3D widget to interactively set the transformation.
The Transform filter showing the 3D widget that can be used to interactively set the transform.
# To create the filter(if Input is not specified, the active source will be# used as the input).>>>transform=Transform(Input=...)# Set the transformation properties.>>>transform.Translate.Scale=[1,2,1]>>>transform.Transform.Translate=[100,0,0]>>>transform.Transform.Rotate=[0,0,0]
The Reflect filter can be used to reflect a dataset along a specific axis plane.
Reflect can be used to reflect any dataset across an axis plane. You can
pick the axis plane to be one of the planes formed by the bounding box of the
dataset. For that, set Plane as XMin , XMax , YMin , YMax ,
ZMin , or ZMax . To reflect across an arbitrary axis plane,
select X , Y , or Z for the Plane property, and then set the
Center to the plane offset from the origin.
This filter reflects the input dataset and produces an unstructured grid
(Section 3.1.7). Thus, the same caveats for
Clip and Threshold filter apply here when dealing with structured
datasets.
The WarpByVector filter can be used to
displace points in original data shown on the left, using the
displacement vectors (indicated by arrow glyphs Section 5.8.1) to
produce the result shown on the right.
WarpByVector can be used to displace point coordinates in an input mesh
using vectors in the dataset itself. You select the vectors to use utilizing the
Vectors property on the Properties panel. ScaleFactor can be
used to scale the displacement applied.
WarpByScalar is similar to WarpByVector in the sense that it warps
the input mesh. However, it does so using a scalar array in the input dataset. The
direction of displacement can either be explicitly specified using the
Normal property, or you can check UseNormal to use normals at the
point locations.
Glyph is used to place markers or glyphs at point locations in the input
dataset. The glyphs can be oriented or scaled based on vector and
scalar attributes on those points.
To create this filter in paraview, you can use the Filters menu,
as well as the
button on the Common filters toolbar. You first select
the type of glyph using one of the options in GlyphType . The choices
include Arrow , Sphere , Cylinder , etc. Next, you select the point
arrays to use as the OrientationArray (selecting Noorientationarray
will result in the glyphs not being oriented). Similarly, you select a point array
to serve as the glyph ScaleArray (no scaling is performed if Noscalearray
is chosen).
If the ScaleArray is set to a vector array, the VectorScaleMode
property is available to select which properties of the vector should be used
to transform each glyph. If ScalebyMagnitude is chosen, then the glyph
at a point will be scaled by the magnitude of the vector at that point. If
ScalebyComponents is chosen, glyphs will be scaled separately in each
dimension by the vector component in that dimension.
The ScaleFactor is used to apply a constant scaling to all the glyphs,
independent of the ScaleArray and VectorScaleMode properties.
Choosing a good scale factor depends on
several things including the bounds on the input dataset, the ScaleArray
and VectorScaleMode selected, and the range for the array selected as the
ScaleArray . You can use the button next to the ScaleFactor widget to have paraview
pick a usually reasonable scale factor value based on the current dataset and
scaling properties.
The Masking properties control which points from the input
dataset get glyphed. The GlyphMode controls how points are selected to be
glyphs (Fig. 5.15). The available options are as follows:
AllPoints : This selects all points in the input dataset for glyphing.
Use this mode with caution and only when the input dataset has relatively few
points. Since all points in the input dataset are glyphed, this can not only
cause visual clutter, but also clog up memory and take a long to time to
generate and render the glyphs.
EveryNthPoints : This elects every \(n^{th}\) point in the input dataset
for glyphing, where \(n\) can be specified using Stride . Setting
Stride to 1 will have the same effect as AllPoints .
UniformSpatialDistribution : This selects a random set of points. The
algorithm works by first computing up to MaximumNumberofSamplePoints
in the space defined by the bounding box of the input dataset. Then, points
in the input dataset that are close to the point in this set of sample points
are glyphed. The Seed is used to seed the random number generator used to
generate the sample points. This ensures that the random sample points are
reproducible and consistent.
Comparison between various GlyphMode s when applied to the same
dataset generated by the Wavelet source.
Did you know?
The Glyph representation can be used for many of the same visualizations
where a Glyph filter might be used. It may offer faster rendering and consume
less memory than the Glyph filter with similar capabilities. In circumstances
where generating a 3D geometry is required, e.g., when exporting glyph geometry
to a file, the Glyph filter is required.
GlyphWithCustomSource is the same as Glyph , except that instead of a limited
set of GlyphType , you can select any data source producing a polygonal
dataset (Section 3.1.8) available in the PipelineBrowser . To use this filter, select the data source you wish to glyph in the
PipelineBrowser and attach this filter to it. You will be presented a dialog
where you can set the Input (which defaults to the source you selected) and
the GlyphSource .
Setting the Input and GlyphSource in the GlyphWithCustomSource filter.
Streamlines generated from the disk_out_ref.ex2 dataset
using the PointSource (left) and the HighResolutionLineSource
(right). On the left, we also added the Tube filter to the output of the
StreamTracer filter to generate 3D tubes rather than 1D polygonal lines,
which can be hard to visualize due to lack of shading.
The StreamTracer filter is used to generate streamlines for vector fields.
In visualization, streamlines refer to curves that are instanteneously
tangential to the the vector field in the dataset. They provide an indication of
the direction in which the particles in the dataset would travel at that instant
in time. The algorithm works by taking a set of points, known as seed
points, in the dataset and then integrating the streamlines starting at these seed
points.
In paraview, you can create this filter using the Filters
menu, as well as the button on the Common
filters toolbar. To use
this filter, you first select the attribute array to use as the Vectors for
generating the streamline. IntegrationParameters let you fine tune the
streamline integration by specifying the direction to integrate,
IntegrationDirection , as well as the type of integration algorithm to
use, IntegratorType . Advanced integration parameters are available in the
advanced view of the Properties panel that let you further tune the
integration, including specifying the step size and others. You use the
MaximumStreamlineLength to limit the maximum length for the streamline –
the longer the length, the longer the generated streamlines.
The Properties panel showing the default properties for the
StreamTracer filter.
Seeds group lets you set how the seed points for generating the streamlines
are produced. You have two options: PointSource , which produces a point
clound around the user-specified Point based on the parameters specified,
and HighResolutionLineSource , which produces seed points along the user-specified
line. You can use the 3D widgets shown in the active RenderView
to interactively place the center for the point cloud or for defining the line.
Did you know?
The StreamTracer filter produces a polydata with 1D lines for each of the
generated streamlines. Since 1D lines cannot be shaded like surfaces in the
RenderView , you can get visualizations where it is hard to follow the
streamlines. To give the streamlines some 3D structure, you can apply the
Tube filter to the output of the streamlines. The properties on the
Tube filter let you control the thickness of the tubes. You can also vary
the thickness of the tubes based on data array, e.g., the magnitude of the
vector field at the sample points in the streamline!
A script using the StreamTracer filter in paraview typically
looks like this:
# find source>>>disk_out_refex2=FindSource('disk_out_ref.ex2')# create a new 'Stream Tracer'>>>streamTracer1=StreamTracer(Input=disk_out_refex2,SeedType='Point Source')>>>streamTracer1.Vectors=['POINTS','V']# init the 'Point Source' selected for 'SeedType'>>>streamTracer1.SeedType.Center=[0.0,0.0,0.07999992370605469]>>>streamTracer1.SeedType.Radius=2.015999984741211# show data in view>>>Show()# create a new 'Tube'>>>tube1=Tube(Input=streamTracer1)# Properties modified on tube1>>>tube1.Radius=0.1611409378051758# show the data from tubes in view>>>Show()
StreamTracer allows you to specify the seed points either as a point cloud
or as a line source. However, if you want to provide your own seed points from
another data producer, use the StreamTracerWithCustomSource . Similar to
GlyphWithCustomSource , this filter allows you to pick a second input
connection to use as the seed points.
Streamlines generated from the disk_out_ref.ex2 dataset using the output of the Slice filter as the Source for seed points.
An example of ResampleWithDataset . On the left is
a multiblock tetrahedra mesh ( Input ). The middle shows
a multiblock unstructured grid ( Source ). The outline of Input is
also shown in this view. The result of applying the filter is shown on
the right
ResampleWithDataset samples the point and cell attributes of one dataset
on to the points of another dataset. The two datasets are supplied to the
filter using its two input ports: Input , which is the dataset that
provides the attributes to resample, and Source , which is the dataset that
provides the points to sample at. This filter is available under the
Filters menu.
ResampleToImage is a specialization of ResampleWithDataset .
The filter takes one input and samples its point and cell attributes onto a
uniform grid of points. The bounds and extents of the uniform grid can be
specified using the properties panel. By default, the bounds are set to the
bounds of the input dataset. The output of the filter is an Image dataset.
An example of ResampleToImage . The left portion shows the input
(unstructured grid), and the middle displays the output image data.
On the right is a volume rendering of the resampled data.
Some operations can be performed more efficiently on uniform grid datasets.
Volume rendering is one such operation. The ResampletoImage filter can
be used to convert any dataset to Image data before performing such operations.
Probe samples the input dataset at a specific point location to obtain the
cell data attributes for the cell containing the point as well as the interpolated point
data attributes. You can either use the SpreadSheetView or the
Information panel to inspect the probed values. The probe location can be
specified using the interactive 3D widget shown in the active RenderView .
The PlotOverLine filter applied to the disk_out_ref.ex2
dataset to plot values at sampled locations along the line. Gaps in the line correspond
to the locations in the input dataset where the line falls outside the dataset.
PlotOverLine will sample the input dataset along the specified line and
then plot the results in LineChartView . Internally, this filter uses the
same mechanism as the Probe filter, probing along the points in the
line to get the containing cell attributes and interpolated point attributes.
Using the Resolution property on the Properties panel, you can control
the number of sample points along the line.
The filters covered in this section are used to add new attribute arrays to the
dataset, which are typically used to add derived quantities to use in pipelines for
further processing.
The Calculator filter computes a new data array or new point coordinates as a
function of existing input arrays. If point-centered arrays are used
in the computation of a new data array, the resulting array will also be
point-centered. Similarly, computations using cell-centered arrays will produce
a new cell-centered array. If the function is computing point coordinates
(requested by checking the CoordinateResults property on the
Properties panel) , the
result of the function must be a three-component vector. The Calculator
interface operates similarly to a scientific calculator. In creating the
function to evaluate, the standard order of operations applies. Each of the
calculator functions is described below. Unless otherwise noted, enclose the
operand in parentheses using the ( and ) buttons.
Clear : Erase the current function.
/: Divide one scalar by another. The operands for this function are not required to be enclosed in parentheses.
*: Multiply two scalars, or multiply a vector by a scalar (scalar multiple). The operands for this function are not required to be enclosed in parentheses.
-: Negate a scalar or vector (unary minus), or subtract one scalar or vector from another. The operands for this function are not required to be enclosed in parentheses.
+: Add two scalars or two vectors. The operands for this function are not required to be enclosed in parentheses.
iHat , jHat , and kHat are vector constants representing unit vectors in the X, Y, and Z directions, respectively.
sin(x) : Compute the sine of a scalar.
cos(x) : Compute the cosine of a scalar.
tan(x) : Compute the tangent of a scalar.
abs(x) : Compute the absolute value of a scalar.
sqrt(x) : Compute the square root of a scalar.
asin(x) : Compute the arcsine of a scalar.
acos(x) : Compute the arccosine of a scalar.
atan(x) : Compute the arctangent of a scalar.
ceil(x) : Compute the ceiling of a scalar.
floor(x) : Compute the floor of a scalar.
sinh(x) : Compute the hyperbolic sine of a scalar.
cosh(x) : Compute the hyperbolic cosine of a scalar.
tanh(x) : Compute the hyperbolic tangent of a scalar.
x^y : Raise one scalar to the power of another scalar. The operands for this function are not required to be enclosed in parentheses.
exp(x) Raise \(e\) to the power of a scalar.
dot(x,y) : Compute the dot product of two vectors x and y.
mag(x) : Compute the magnitude of a vector.
norm(x) : Normalize a vector. The operands are described below. The digits 0-9 and the decimal point are used to enter constant scalar values.
ln(x) : Compute the logarithm of a scalar to the base \(e\).
log10(x) : Compute the logarithm of a scalar to the base 10.
Additional operations are available in the Calculator filter that do not have buttons in the user interface, including:
avg(x,y,z,...) : Average of all the input arguments.
clamp(r0,x,r1) : Clamp x in range between r0 and r1.
cross(x,y) : Compute cross product of two vectors x and y.
equal(x,y) : Equality test between x and y using normalized epsilon.
erf(x) : Error function of x.
erfc(x) : Complimentary error function of x.
frac(x) : Fractional portion of x.
hypot(x,y) : Hypotenuse of x and y, equivalent of sqrt(x*x+y*y).
iclamp(r0,x,r1) : Inverse-clamp x outside of the range r0 and r1. If x is within the range it will snap to the closest bound.
inrange(r0,x,r1) : Returns true when x is within the range r0 and r1.
log1p(x) : Natural logarithm of 1 + x, where x is very small.
log2(x) : Base 2 logarithm of x.
logn(x,n) : Base N logarithm of x where n is a positive integer.
min(x,y) : Compute minimum of two scalars.
max(x,y) : Compute maximum of two scalars.
mul(z,y,z,...) : Multiply all the inputs together.
ncdf(x) : Normal cumulative distribution function.
not_equal(x,y) : Not-equal test between x and y using normalised epsilon.
pow(x,y) : x to the power of y.
root(x,n) : nth-root of x where n is a positive integer.
round(x) : Round x to the nearest integer
roundn(x,n) : Round x to n decimal places.
sgn(x) : Compute the sign of x: -1 where x < 0, +1 where x > 0, and 0 otherwise.
sum(x,y,z,...) : Sum of all the inputs.
trunc(x) : Integer portion of x.
acosh(x) : Inverse hyperbolic cosine of x expressed in radians.
asinh(x) : Inverse hyperbolic sine of x expressed in radians.
atan2(x,y) : Arc tangent of (x / y) expressed in radians.
atanh(x) : Inverse hyperbolic tangent of x expressed in radians.
cot(x) : Cotangent of x.
csc(x) : Cosecant of x.
sec(x) : Secant of x.
sinc(x) : Cardinal sine of x.
deg2rad(x) : Convert x from degrees to radians.
deg2grad(x) : Convert x from degrees to gradians.
rad2deg(x) : Convert x from radians to degrees.
grad2deg(x) : Convert x from gradians to degrees.
The following equalities and inequalities are available:
== or = : True only if x is strictly equal to y.
<> or != : True only if x does not equal y.
< : True only if x is less than y.
<= : True only if x is less than or equal to y.
> : True only if x is greater than y.
>= : True only if x is greater than or equal to y.
The following conditionals and boolean operators are available:
if(x,y,z) : If x evaluates to true, then y, otherwise z.
true : True state.
false : False state.
xandy : Logical and, true only if x and y are both true.
mand(x,y,z,...) : Multi-input logical and, true only if all arguments are true.
mor(x,y,z,...) : Multi-input logical or, true if any arguments are true.
xnandy : Logical nand, true only if either x or y is false.
xnory : Logical nor, true only if neither x or y is false.
notx : Logical not, evaluate to the opposite of the input boolean value.
xory : Logical or, true if either x or y is true.
xxory : Logical xor, true only if the logical state of x or y are different.
xxnory : True if and only if both logical inputs are the same.
The Scalars menu lists the names of the scalar arrays and the components of
the vector arrays of either the point-centered or
cell-centered data. The Vectors menu lists the names of the point-centered or
cell-centered vector arrays. The function will be computed for each point (or
cell) using the scalar or vector value of the array at that point (or cell). The
filter operates on any type of dataset, but the input dataset must have at
least one scalar or vector array. The arrays can be either point-centered or
cell-centered. The Calculator filter’s output is of the same dataset type as
the input.
Did you know?
It used to be a common use-case for the Calculator filter to convert three input
scalars into a vector array. For that, the Function would look something like:
\(scalar_x * iHat + scalar_y * jHat + scalar_z * kHat\).
Now, the Merge Vector Components filter provides a simpler way to do this
by simply selecting the three scalars to combine into a vector array.
The Properties panel for the Calculator filter showing the advanced properties.
The Properties panel provides access to several options for this filter.
Checking CoordinateResults , ResultNormals , or ResultTCoords
will set the computed array as the point coordinates, normals, or texture
coordinates, respectively. ResultArrayName is used to specify a name for
the computed array. The default is Result.
Sometimes, the expression can yield invalid values. To replace all invalid
values with a specific value, check the ReplaceInvalidResults checkbox and
then enter the value to use to replace invalid values using the
ReplacementValue . The output array data type is set with the ResultArrayType
property.
To ease the reuse of expressions, three helper buttons are also present to load an expression,
save the current one and inspect the list of already saved expressions from the ExpressionManager.
ParaView provides an ExpressionManager to ease the expression property configuration
by storing expressions, and giving quick access to them. Each expression can be named
and has an associated group so it is easy to filter Python expressions from others.
This feature comes in two parts:
From the PropertyPanel, the one-line property text entry is augmented with:
a drop down list to access existing expressions
a SaveCurrentExpression button
a shortcut to the ChooseExpression dialog
Expression-related buttons in the Properties Panel.
The ChooseExpression dialog, also accessible from the Tools > Manage Expressions menu item, is an editable and searchable list of the stored expressions. ParaView keeps track of them through the settings, but they can also be exported to a JSON file for backup and sharing.
The PythonCalculator is similar to Calculator in that
it processes one or more input arrays based on an expression provided by the
user to produce a new output array. However, it uses Python (and
NumPy) to do the computation. Therefore, it provides more expressive
expression capabilities.
Specify the Expression to use, the ArrayAssociation to indicate
the array association ( PointData or CellData ),
the name of output array ( ArrayName ), and a toggle
that controls whether the input arrays are copied to the output ( CopyArray ).
The PythonCalculator also integrated the ExpressionManager described in Section 5.9.2.
Start by creating a Sphere source and applying the PythonCalculator to it. As
the first expression, use the following and apply:
5
This should create an array name result in the output point data. Note
that this is an array that has a value of 5 for each point. When the expression
results in a single value, the calculator will automatically make a constant
array. Next, try the following:
Normals
Now, the result array should be the same as the input array Normals. As
described in detail later, various functions are available through the
calculator. For example, the following is a valid expression:
sin(Normals)+5
It is very important to note that the PythonCalculator has to produce one value
per point or cell depending on the Array Association parameter. Most of the
functions described here apply individually to all point or cell values and
produce an array the same dimensions as the input. However, some of them, such
as min() and max() , produce single values.
Common Errors
In the ProgrammableFilter , all the functions in
vtk.numpy_interface.algorithms are imported prior to executing the script.
As a result, some built-in functions, such as min and max , are
clobbered by that import. To use the built-in functions, import the import__builtin__
module and access those functions with, e.g.,
__builtin__.min and __builtin__.max
There are several ways of accessing input arrays within expressions. The
simplest way is to access it by name:
sin(Normals)+5
This is equivalent to:
sin(inputs[0].PointData['Normals'])+5
The example above requires some explanation. Here, inputs[0] refer to the
first input (dataset) to the filter. PythonCalculator can accept multiple
inputs. Each input can be accessed as inputs[0] , inputs[1] , … You
can access the point or cell data of an input using the .PointData or
.CellData qualifiers. You can then access individual arrays within the
point or cell data containers using the [] operator. Make sure to use
quotes or double-quotes around the array name. Arrays that have names with
certain characters (such as space, +, -, *, /) can only be accessed using this
method.
Certain functions apply directly on the input mesh. These filters expect an
input dataset as argument. For example,
area(inputs[0])
For data types that explicitly define the point coordinates, you can access the
coordinates array using the .Points qualifier. The following extracts the
first component of the coordinates array:
inputs[0].Points[:,0]
Note that for certain data types, mainly image data (uniform rectilinear grids)
and rectilinear grids, point coordinates are defined implicitly and cannot be
accessed as an array.
The PythonCalculator can be used to compare multiple datasets, as shown by
the following example.
Go to the Menu Bar, and select File > Disconnect to
clear the Pipeline.
Select Source > Mandelbrot, and then click
Apply, which will set up a default version of the Mandelbrot Set. The data for
this set are stored in a \(251 \times 251\) scalar array.
Select Source > Mandelbrot again, and then go to the Properties panel and
set the Maximum Number of Iterations to 50. Click Apply , which will set up
a different version of the Mandelbrot Set, represented by the same size array.
Hold the Shift key down and select both of the Mandelbrot entries in the
Pipeline Inspector, and then go to the Menu Bar, and select Filter >
Python Calculator. The two Mandelbrot entries will now be shown as linked, as
inputs, to the PythonCalculator .
In the Properties panel for the Python
Calculator filter, enter the following into the Expression box:
This expression specifies the difference between the second and the first
Mandelbrot arrays. The result is saved in a new array called results . The
prefixes in the names for the array variables, inputs[1] and
inputs[0] , refer to the first and second Mandelbrot entries, respectively,
in the Pipeline. PointData specifies that the inputs contain point values.
The quoted label 'Iterations' is the local name for these arrays. Click
Apply to initiate the calculation.
Click the Display tab in the PropertiesPanel for the PythonCalculator ,
and go to the first tab to the right of the Color by label. Select the
item results in that tab, which will cause the display window to the right to
show the results of the expression we entered in the PythonCalculator . The
scalar values representing the difference between the two Mandelbrot arrays are
represented by colors that are set by the current color map (see Edit Color
Map… for details).
There are a few things to note:
PythonCalculator will always copy the mesh from the first input to its output.
All operations are applied point-by-point. In most cases, this requires
that the input meshes (topology and geometry) are the same. At the least, it
requires that the inputs have the same number of points and cells.
In parallel execution mode, the inputs have to be distributed exactly the
same way across processes.
The PythonCalculator supports all of the basic arithmetic operations using the
\(+\), \(-\), \(*\) and \(/\) operators. These are always applied element-by-element to
point and cell data including scalars, vectors, and tensors. These operations
also work with single values. For example, the following adds 5 to all
components of all Normals.
Normals+5
The following adds 1 to the first component, 2 to the second component, and 3 to
the third component:
Normals+[1,2,3]
This is specially useful when mixing functions that return single values. For
example, the following normalizes the Normals array:
A common use case in a calculator is to work on one component of an array. This
can be accomplished with the following:
Normals[:,0]
The expression above extracts the first component of the Normals vector. Here,
: is a placeholder for “all elements”. One element can be extracted by replacing
: with an index. For example, the following creates a constant array from the
first component of the normal of the first point:
Normals[0,0]
Alternatively, the following assigns the normal of the first point to all points:
Normals[0,:]
It is also possible to create a vector array from two or three scalar arrays using the make_vector() function:
make_vector(velocity_x,velocity_y,velocity_z)
For temporal datasets, you also have access to the dataset timestep index or time value
in the expression as t_index or time_index , and t_value or time_value
respectively. When dealing with multiple inputs, you can specify the same variable names scoped on the
appropriate input e.g. inputs[0].t_index .
The locations of points are available in the Points variable for datasets that define explicit points positions.
In some datasets, field data is used to store global data values not associated with cells or points.
To use field data in a PythonCalculator expression, access it with the FieldData dictionary
available in the input as in the following example:
Under the cover, the PythonCalculator uses NumPy. All arrays in the
expression are compatible with NumPy arrays and can be used where NumPy arrays
can be used. For more information on what you can do with these arrays, consult
with the NumPy references:cite:numpy.
The following is a list of functions available in the PythonCalculator .
Note that this is a partial list, since most of the NumPy and SciPy functions
can be used in the PythonCalculator . Many of these functions can take
single values or arrays as argument.
abs(x) : Returns the absolute value(s) of \(x\).
add(x,y) : Returns the sum of two values. \(x\) and \(y\) can be single values or arrays. This is the same as \(x+y\).
area(dataset) : Returns the surface area of each cell in a mesh.
aspect(dataset) : Returns the aspect ratio of each cell in a mesh.
aspect_gamma(dataset) : Returns the aspect ratio gamma of each cell in a mesh.
condition(dataset) : Returns the condition number of each cell in a mesh.
cross(x,y) : Returns the cross product for two 3D vectors from two arrays of 3D vectors.
curl(array) : Returns the curl of an array of 3D vectors.
divergence(array) : Returns the divergence of an array of 3D vectors.
divide(x,y) : Element-by-element division. \(x\) and \(y\) can be single
values or arrays. This is the same as math:frac{x}{y}.
det(array) : Returns the determinant of an array of 2D square matrices.
determinant(array) : Returns the determinant of an array of 2D square matrices.
diagonal(dataset) : Returns the diagonal length of each cell in a dataset.
dot(a1,a2) : Returns the dot product of two scalars/vectors of two array of scalars/vectors.
eigenvalue(array) : Returns the eigenvalue of an array of 2D square matrices.
eigenvector(array) : Returns the eigenvector of an array of 2D square matrices.
exp(x) : Returns \(e^x\).
gradient(array) : Returns the gradient of an array of
scalars or vectors.
inv(array) : Returns the inverse an array of 2D square matrices.
inverse(array) : Returns the inverse of an array of 2D square matrices.
jacobian(dataset) : Returns the jacobian of an array of 2D square matrices.
laplacian(array) : Returns the jacobian of an array of scalars.
ln(array) : Returns the natural logarithm of an array of scalars/vectors/tensors.
log(array) : Returns the natural logarithm of an array of scalars/vectors/tensors.
log10(array) : Returns the base 10 logarithm of an array of scalars/vectors/tensors.
make_point_mask_from_NaNs(dataset,array) : This function will create a ghost array corresponding to an input with NaN values. For each NaN value, the output array will have a corresponding value of vtk.vtkDataSetAttributes.HIDDENPOINT . These values are also combined with any ghost values that the dataset may have.
make_cell_mask_from_NaNs(dataset,array) : This function will create a ghost array corresponding to an input with NaN values. For each NaN value, the output array will have a corresponding value of vtk.vtkDataSetAttributes.HIDDENCELL . These values are also combined with any ghost values that the dataset may have.
max(array) : Returns the maximum value of the array as a single value. In parallel, compute the max accross processes.
max_angle(dataset) : Returns the maximum angle of each cell in a dataset.
mag(a) : Returns the magnitude of an array of scalars/vectors.
mean(array) : Returns the mean value of an array of scalars/vectors/tensors. In parallel, compute the mean accross processes.
min(array) : Returns the minimum value of the array as a single value. In parallel, compute the min accorss processes.
min_angle(dataset) : Returns the minimum angle of each cell in a dataset.
mod(x,y) : Same as remainder \((x, y)\).
multiply(x,y) : Returns the product of \(x\) and \(y\). \(x\) and \(y\) can be
single values or arrays. Note that this is an element-by-element operation when
\(x\) and \(y\) are both arrays. This is the same as \(x \times y\).
negative(x) : Same as \(-x\).
norm(a) : Returns the normalized values of an array of scalars/vectors.
power(x,a) : Exponentiation of \(x\) with \(a\). Here, both \(x\) and \(a\) can
either be a single value or an array. If \(x\) and \(y\) are both arrays, a one-by-one
mapping is used between two arrays.
reciprocal(x) : Returns \(\frac{1}{x}\).
remainder(x,y) : Returns \(x - y \times floor(\frac{x}{y})\). \(x\) and \(y\) can be single values or arrays.
rint(x) : Rounds \(x\) to the nearest integer(s).
shear(dataset) : Returns the shear of each cell in a dataset.
skew(dataset) : Returns the skew of each cell in a dataset.
square(x) : Returns \(x*x\).
sqrt(x) : Returns \(\sqrt[2]{x}\).
strain(array) : Returns the strain of an array of 3D vectors.
subtract(x,y) : Returns the difference between two values. \(x\) and
y can be single values or arrays. This is the same as \(x - y\).
surface_normal(dataset) : Returns the surface normal of each cell in a dataset.
trace(array) : Returns the trace of an array of 2D square matrices.
volume(dataset) : Returns the volume normal of each cell in a dataset.
vorticity(array) : Returns the vorticity/curl of an array of 3D vectors.
vertex_normal(dataset) : Returns the vertex normal of each point in a dataset.
The Gradient filter computes the gradient of a cell or point data array for
any type of dataset.
For unstructured grids, the gradient for cell data corresponds to the cell derivatives.
For point data, the gradient at a given point is computed as the average of the
derivatives of the cells to which the point belongs.
For structured grids, the gradient is computed using central differencing, except
on the boundary of the dataset where forward and backward differencing is used for
the boundary elements.
This filter can optionally compute the divergence, vorticity (also known as the
curl), and Q-criterion. A 3-component array is required in order to compute these
quantities. By default, only the gradient computation is enabled.
In the case of a uniform rectilinear grid (see Section 3.1.3),
a specific implementation which efficiently computes the gradient of point data arrays
is also available. This implementation extends the use of central differencing
on the boundary elements after duplication of the boundary values. To activate
this option, set the BoundaryMethod property to Smoothed, as shown in
Fig. 5.28.
The Properties Panel for the Gradient filter applied to a uniform
structured grid.
The MeshQuality filter creates a new cell array containing a geometric
measure of each cell’s fitness. Different quality measures can be chosen for
different cell shapes.
TriangleQuality indicates which quality measure will be used to evaluate
triangle quality. The RadiusRatio is the size of a circle circumscribed by a
triangle’s three vertices divided by the size of a circle tangent to a triangle’s three
edges. The EdgeRatio is the ratio of the longest edge length to the shortest
edge length.
QuadQuality indicates which quality measure will be used to evaluate
quad cells.
TetQuality indicates which quality measure will be used to evaluate
tetrahedral quality. The RadiusRatio is the size of a sphere circumscribed by a
tetrahedron’s four vertices divided by the size of a circle tangent to a
tetrahedron’s four faces. The EdgeRatio is the ratio of the longest edge length to
the shortest edge length. The CollapseRatio is the minimum ratio of height of a
vertex above the triangle opposite it, divided by the longest edge of the
opposing triangle across all vertex/triangle pairs.
HexQualityMeasure indicates which quality measure will be used to evaluate
quality of hexahedral cells.
This includes the ProgrammableFilter and ProgrammableSource . For
these filters/sources, you can add Python code to do the data generation or
processing. We’ll cover writing Python code for these in
Section 5.
If you use some filters more than others, you can organize them in the Filters > Favorites menu.
This can be done from the context menu in the pipeline or through the Filters > Manage Favorites
menu as shown in Fig. 5.29. In this dialog you can create categories and
subcategories. It supports drag’n’drop operation to sort and move filters and categories.
Moreover, Favorites are highlighted in the other filter submenus on supported platforms.
Favorites are saved in user settings so they can be used in other subsequent ParaView sessions.
The Favorites Manager dialog. Left: the list of available filters. Right: the favorites, organized into categories.
The pipeline model that ParaView presents is very convenient for exploratory
visualization. The loose coupling between components provides a very flexible
framework for building unique visualizations, and the pipeline structure allows
you to tweak parameters quickly and easily.
The downside of this coupling is that it can have a larger memory footprint.
Each stage of this pipeline maintains its own copy of the data. Whenever
possible, ParaView performs shallow copies of the data so that different stages
of the pipeline point to the same block of data in memory. However, any filter
that creates new data or changes the values or topology of the data must
allocate new memory for the result. If ParaView is filtering a very large mesh,
inappropriate use of filters can quickly deplete all available memory.
Therefore, when visualizing large datasets, it is important to understand the
memory requirements of filters.
Please keep in mind that the following advice is intended only for when dealing
with very large amounts of data and the remaining available memory is low. When
you are not in danger of running out of memory, the following advice is not
relevant.
When dealing with structured data, it is absolutely important to know what
filters will change the data to unstructured. Unstructured data has a much
higher memory footprint, per cell, than structured data because the topology
must be explicitly written out. There are many filters in ParaView that will
change the topology in some way, and these filters will write out the data as an
unstructured grid, because that is the only dataset that will handle any type of
topology that is generated. The following list of filters will write out a new
unstructured topology in its output that is roughly equivalent to the input.
These filters should never be used with structured data and should be used with
caution on unstructured data.
Append Datasets
Extract Edges
Subdivide
Append Geometry
Linear Extrusion
Tessellate
Clean
Loop Subdivision
Tetrahedralize
Clean to Grid
Reflect
Triangle Strips
Connectivity
Rotational Extrusion
Triangulate
D3
Shrink
Delaunay 2D/3D
Smooth
Technically, the Ribbon and Tube filters should fall into this list.
However, as they only work on 1D cells in poly data, the input data is usually
small and of little concern.
This similar set of filters also outputs unstructured grids, but also tends to
reduce some of this data. Be aware though that this data reduction is often
smaller than the overhead of converting to unstructured data. Also note that the
reduction is often not well balanced. It is possible (often likely) that a
single process may not lose any cells. Thus, these filters should be used with
caution on unstructured data and extreme caution on structured data.
Clip
Extract Selection
Decimate
Quadric Clustering
Extract Cells by Region
Threshold
Similar to the items in the preceding list, ExtractSubset performs data
reduction on a structured dataset, but also outputs a structured dataset. So the
warning about creating new data still applies, but you do not have to worry
about converting to an unstructured grid.
This next set of filters also outputs unstructured data, but it also performs a
reduction on the dimension of the data (for example 3D to 2D), which results in
a much smaller output. Thus, these filters are usually safe to use with
unstructured data and require only mild caution with structured data.
Cell Centers
Feature Edges
Contour
Mask Points
Extract CTH Fragments
Outline (curvilinear)
Extract CTH Parts
Slice
Extract Surface
Stream Tracer
The filters below do not change the connectivity of the data at all. Instead,
they only add field arrays to the data. All the existing data is shallow copied.
These filters are usually safe to use on all data.
Block Scalars
Octree Depth Scalars
Calculator
Point Data to Cell Data
Cell Data to Point Data
Process Id Scalars
Curvature
Random Vectors
Elevation
Resample with dataset
Generate Surface Normals
Surface Flow
Gradient
Surface Vectors
Level Scalars
Texture Map to…
Median
Transform
Mesh Quality
Warp (scalar)
Octree Depth Limit
Warp (vector)
This final set of filters either add no data to the output (all data of
consequence is shallow copied) or the data they add is generally independent of
the size of the input. These are almost always safe to add under any
circumstances (although they may take a lot of time).
Annotate Time
Outline
Append Attributes
Outline Corners
Extract Block
Plot Global Variables Over Time
Extract Datasets
Plot Over Line
Extract Level
Plot Selection Over Time
Glyph
Probe Location
Group Datasets
Temporal Shift Scale
Histogram
Temporal Snap-to-Time-Steps
Integrate Variables
Temporal Statistics
Normal Glyphs
There are a few special case filters that do not fit well into any of the
previous classes. Some of the filters, currently TemporalInterpolator and
ParticleTracer , perform calculations based on how data changes over time.
Thus, these filters may need to load data for two or more instances of time,
which can double or more the amount of data needed in memory. The TemporalCache filter will also hold data for multiple instances of time. Keep in mind
that some of the temporal filters such as the Temporal Statistics and the
filters that plot over time may need to iteratively load all data from disk.
Thus, it may take an impractically long amount of time even if does not require
any extra memory.
The ProgrammableFilter is also a special case that is impossible to
classify. Since this filter does whatever it is programmed to do, it can fall
into any one of these categories.
When dealing with large data, it is best to cull out data whenever possible and
do so as early as possible. Most large data starts as 3D geometry and the
desired geometry is often a surface. As surfaces usually have a much smaller
memory footprint than the volumes that they are derived from, it is best to
convert to a surface early on. Once you do that, you can apply other filters in
relative safety.
A very common visualization operation is to extract isosurfaces from a volume
using the Contour filter. The Contour filter usually outputs geometry much
smaller than its input. Thus, the Contour filter should be applied early if
it is to be used at all. Be careful when setting up the parameters to the
Contour filter because it still is possible for it to generate a lot of
data which can happen if you specify many isosurface values. High frequencies
such as noise around an isosurface value can also cause a large, irregular
surface to form.
Another way to peer inside of a volume is to perform a Slice on it. The
Slice filter will intersect a volume with a plane and allow you to see the
data in the volume where the plane intersects. If you know the relative location
of an interesting feature in your large dataset, slicing is a good way to view
it.
If you have little a priori knowledge of your data and would like to
explore the data without the long memory and processing time for the full
dataset, you can use the ExtractSubset filter to subsample the data. The
subsampled data can be dramatically smaller than the original data and should
still be well load balanced. Of course, be aware that you may miss small
features if the subsampling steps over them and that once you find a feature you
should go back and visualize it with the full dataset.
There are also several features that can pull out a subset of a volume:
Clip , Threshold , ExtractSelection , and ExtractSubset can
all extract cells based on some criterion. Be aware, however, that the extracted
cells are almost never well balanced; expect some processes to have no cells
removed. All of these filters, with the exception of ExtractSubset , will
convert structured data types to unstructured grids. Therefore, they should not
be used unless the extracted cells are of at least an order of magnitude less
than the source data.
When possible, replace the use of a filter that extracts 3D data with one that
will extract 2D surfaces. For example, if you are interested in a plane through
the data, use the Slice filter rather than the Clip filter. If you are
interested in knowing the location of a region of cells containing a particular
range of values, consider using the Contour filter to generate surfaces at
the ends of the range rather than extract all of the cells with the
Threshold filter. Be aware that substituting filters can have an effect on
downstream filters. For example, running the Histogram filter after
Threshold will have an entirely different effect than running it after the
roughly equivalent Contour filter.
A typical visualization process has two components: setting up the
visualization scene and performing the analysis of the results to gain insight.
It is not uncommon for this process to be iterative. Often, what you are looking
for drives from what filters you should use to extract the relevant information from
the input datasets and what views will best represent that data. One of the
ways of evaluating the results is inspecting the data or probing into it by
identifying elements of interest. ParaView data selection mechanisms are
designed specifically for such use-cases. In this chapter, we take a closer look
at various ways of selecting data in ParaView and making use of these selections
for data analysis.
Broadly speaking, selection refers to selecting elements (either cells, points,
rows (in case of tabular datasets), etc.) from datasets. Since data is ingested
into ParaView using readers or sources and transformed using filters, when you
create a selection, you are selecting elements from the dataset produced as the
output of source, filter, or any such pipeline module.
There are many ways to create selections. Several views provide means to
create specific selections. For example, in the SpreadSheetView , which
shows the data attributes as a spreadsheet, you can simply click on any row to
select that row. You can, of course, use the ⇧ and CTRL (or
⌘) keys to select multiple rows, as in typical spreadsheet-based
applications.
While this seems like an exercise in futility, you are hardly achieving anything
by highlighting rows in a spreadsheet. What transforms this into a key tool is the
fact that selections are linked among views (whenever possible). Linked
selection means that you select an element from a dataset in a specific view.
All other views that are showing the same dataset will also highlight the
selected elements.
Linked selection between views allows you to select elements in a view
and view them in all other views showing the selected data. In this demo, as we
select rows in the SpreadSheetView ,
the corresponding points in the 3DView get highlighted.
To make this easier, let’s try a quick demo:
Starting with a fresh paraview session, create a sample dataset
using the Sources > Wavelet menu, and then click the Apply button. If you
are using paraview with a default setup, that should result in a
dataset outline being shown in the default RenderView . Next, let’s split
the view and create SpreadSheetView . The SpreadSheetView will
automatically show the data produced by the Wavelet source. Upon closer
inspection of the header in the SpreadSheetView , we see that the view
is showing the PointData or point attributes associated with the dataset.
Now we have the same dataset, the data produced by the Wavelet source,
shown in two views. Now, highlight a few rows in the SpreadSheetView
by clicking on them. As soon as you start selecting rows, the RenderView
will start highlighting some points in space as tiny magenta specks
( Fig. 6.1). That’s linked selection in
action! What is happening is that, as you highlight rows in the SpreadSheetView ,
you are creating a selection for selecting points (since the view is
showing PointData ) corresponding to the rows. Due to the linking of
selections between views, any other view that is showing the dataset (in this
case, the RenderView ) will also highlight the selected points.
Of course, if you want to select cells instead of points, switch the
SpreadSheetView to show cells by flipping the Attribute combo-box to
CellData and then highlight rows. The RenderView will show the
selected cells as a wireframe, rather than points.
Conversely, you could have created the selection in the RenderView , and the
SpreadSheetView will also highlight the selected elements. We will see how
to create such selection later in this chapter.
The first thing to note is that, when you create a new selection, the existing selection
is cleared. Thus, there is at most one active selection in the application at any
given time. As we shall see, certain views provide ways of expanding on the
existing selection.
The second thing to note is that selections are transient, i.e., they cannot
be undone/redone or saved in state files and loaded back. Nor can you apply
filters or other transformation to the selections themselves. There are cases,
however, where you may want to subset your dataset using the selection defined
interactively and then apply filters and other analysis to that extracted
subset. For that, there are filters available, namely ExtractSelection
and PlotSelectionOverTime , that can capture the active selection in as
the filter parameters and then produce a new dataset that is comprised of the
selected elements.
The third thing to note is that there are different types of selections, e.g.,
id-based selections, where the selected elements are identified by their
indices; frustum-based selections, where the selected elements are those that
intersect a frustum defined in 3D space; query-based selections, where the
selected elements are those that match the specified query string; and so on.
Views provide a convenient mechanism for creating selections interactively.
Views like RenderView can create multiple types of selection (id- or
frustum-based selections for selecting points and cells), while others like the
SpreadSheetView and LineChartView only support one type (id-based
selections for points or cells).
To create a selection in the RenderView , you use the toolbar at
the top of the view frame. There are two ways of selecting cells,
points or blocks in ParaView: interactive and non-interactive.
ParaView enters a non-interactive selection mode when you
click one of the non-interactive selection buttons:
The type of selection you are
creating will depend on the button you clicked. Once in
non-interactive selection mode, the cursor will switch to cross-hair
and you can click and drag to create a selection region. Once you
release the mouse,
ParaView will attempt to create a selection for any elements in the selection
region and will go back to default interaction mode.
To create a selection for cells visible in the view, use the
button. For selecting
visible points, use the
button instead. Visible cells (and points) are only those cells (or
points) that are currently rendered on the screen. Thus, elements that
are occluded or are too small to be rendered on the screen will not be
selected. If you want to select all data elements that intersect the
view frustum formed by the selection rectangle you drew on the screen,
use the button (or
for points). In this
case, all elements, visible or otherwise, that are within the 3D space
defined by the selection frustum are selected.
To create a selection for blocks visible in the view use the
button. Note that there is no frustum
selection for blocks.
While most selection modes allow you to define the selection region as a rectangle,
(and for points) enables you to
define the selection region as a closed polygon. However, this is limited to
surface elements (i.e., no frustum-based selection).
ParaView enters an interactive selection mode when you
click on one of the interactive selection buttons:
. In interactive
selection mode, you act on visible elements (cells or
points). ParaView highlights elements of the dataset as you move
the cursor over them. An element can be selected by clicking on
it. Clicking repeatedly on different elements adds them to the
selection. End the interactive selection mode by clicking on
the interactive selection button pushed in or by pressing the
Esc key. This mode is also ended when you enter a
non-interactive selection mode. Use
to select all cells with the same value in the current color array as the
cell underneath the cursor (only available for idtype arrays). Use
to do the same as the previous
icon for point data arrays. You can use the
button to
interactively select cells of the dataset and use the
button to
interactively select points.
When there are selected elements, the
button can be used to clear the selection.
Several of these buttons have hotkeys too, such as S for visible
cell selection, D for visible points selection, F for
frustum-based cell selection, and G for frustum-based point selection. If
you notice, these are keys are right next to each other on the keyboard,
starting with S, and are in the same order as the toolbar buttons themselves.
Result of a frustum cell selection on disk_out_ref.ex2 dataset
showing the frustum used to identify selected cells. All cells that fall in
that frustum or that intersect it are selected, irrespective of whether they were visible from
the view angle when the selection was made.
Did you know?
You can expand the current selection by keeping the CTRL (or ⌘) key pressed
when clicking and dragging in selection mode. paraview will then add the current
selection. You can also subtract from the current selection using the ⇧, or
even toggle using CTRL (or ⌘) + ⇧. Selection modifier buttons, in the
toolbar, can be used for the same effect. Add : , remove :
, toggle : . These modifiers do not work,
however, if the selected data is different from the current selection. If so, the
current selection will be cleared (as is the norm) and then the new selection will be created.
To create a selection in the SpreadSheetView , you simply click on the
corresponding rows in the spreadsheet. You can use the CTRL (or
⌘) and ⇧ keys to add to the selection.
Based on which data attribute the view is currently showing, i.e., PointData , CellData , or RowData , the selection will select points,
cells, or rows, respectively.
LineChartView enables you to select the elements corresponding to the
plotted data values. The selection interaction is similar to RenderView .
By default, you are in the interaction mode. You enter selection mode to create a
selection by using the buttons in the view toolbar for creating a rectangular
selection or a polygonal selection
. Once in selection mode, you
can click and drag to define the selection region. The selection is created once
you release the mouse press.
When a new selection is created, by default, it
will clear any existing selection in the view.
The selection modifier buttons in the view toolbar
can be used to control whether a new selection adds to selected elements
, removes
points from the selected elements , or
toggles it . These modifier
buttons are mutually exclusive and modal, i.e., they remain pressed until you
click to unpress them or until you press another modifier button.
CTRL (or ⌘) and ⇧ can also be used to
add to/subtract from the selection.
Selection in LineChartView can be used to locate elements
matching attribute criteria. In this visualization, by generating a scatter
plot plotting Pres against Temp in the disk_out_ref.ex2 dataset by
selecting the top-left corner of the LineChartView , we can easily locate
elements in the high Pres, low Temp regions in the dataset.
Views provide mechanisms to create selections interactively. Selections in chart
views and SpreadSheetView can be used to select elements with certain data
properties, rather than spatial locations
( Fig. 6.3). For a richer data-based selection
for selecting elements matching certain criteria, you can use the FindData
mechanism in paraview.
The FindData panel can be accessed from the Edit menu, :View menu,
or by using the keyboard shortcut V or the
button on the MainControls toolbar.
The FindData panel can be split into three sections,
reflecting how you would use this dialog. The CreateSelection section
helps you define the selection criteria. This identifies which elements, cells or
points, are to be selected. The SelectedData section shows the
results from the most recent selection. They are shown in a tabular view similar
to the Spreadsheet view. Finally, the SelectionDisplay section
lets you change how the selected elements are displayed in the active view.
The FindData panel can be used to find
data elements matching specific conditions. In this example, we are selecting
all Points in Wavelet1 dataset where RTData is \(>= 150\).
You can create selections in the FindData panel using
the widgets under the CreateSelection section. First, choose the data
producer. This is the source or filter from which you want to select
elements from. Next choose the element type. If you want to select cells,
choose Cell, for points choose Point and so on. The next step is to
define the selection criteria. The left-most combo-box is used to
select the array of interest. The available options reflect the data array
currently available on the dataset. The next combo-box is used to select the
operator. Options include the following:
is matches a single value
isinrange matches a range of values specified by min and max
isoneof` matches a list of comma-separated values
is>= matches all values greater than or equal to the specified value
is<= matches all values lesser than or equal to the specified value
ismin matches the minimum value for the array for the current time step
ismax matches the maximum value for the array for the current time step
is<=mean matches values lesser than or equal to the mean
is>=mean matches values greater than or equal to the mean
ismean matches values equal to the mean within the specified tolerance
Based on your selection of the operator, input widgets will be shown next to
this combo-box, where you enter the corresponding values. For example, for isbetween, you enter the min and max values for defining the range in the two
text entry widgets.
Multiple selection criteria can be combined together. For example, you want to
select all points with Temp >= 100andPres <= mean, simply setup two
expressions using the button.
Once you are satisfied with the selection criteria, hit the FindData
button. On success, the CurrentSelection
spreadsheet will update to show the selected elements. Use the Attribute
combo-box to change which element types are shows in the spreadsheet.
Similar to selecting in views, once you create a selection, any view showing the
selected data will also highlight the selected elements, if possible. For example, the
RenderView will show a colored wireframe marking the selected elements,
SpreadSheetView will highlight the rows, and so on. The SelectionDisplay
section lets you change how the selection is displayed in the active view.
Currently, it is primarily designed for RenderView. In the
future, however, it could support changing selection attributes for other views as well.
The available options allow you select the color to use to show the selected
elements, as well as the data attributes to use to label the cells/points. For finer
control on the label formatting, color, font, etc., use the
. That will pop up the EditLabelProperties dialog
( Fig. 6.5).
SelectionLabelProperties dialog for controlling
selection labelling parameters.
Did you know?
Besides creating new selections, the FindData dialog can also be used
to inspect the current selection made from outside the dialog. For
example, if you select elements in the RenderView using the options
described in Section Section 6.2.1, the CurrentSelection component in the FindData dialog will indeed update to
reflect the newly selected elements. Furthermore, you can change its display
properties and extract this selection using the extraction buttons
(which we will cover in Section Section 6.6).
Another way to create selections is through ParaView’s Python scripting interface.
Python functions exist that are analogous to the selection operations available in the ParaView
RenderView and FindData dialog. Let’s take a look at an example.
# import the selection modulefromparaview.selectionimport*renderView1=GetActiveView()# Create an initial rectangular selection in the render viewSelectSurfacePoints(Rectangle=[200,321,600,744],View=renderView1)# Add points within a polygon in the active viewSelectSurfacePoints(Polygon=[180,200,190,400,322,300],Modifier='ADD')# Subtract points with another rectangleSelectSurfacePoints(Rectangle=[300,400,500,700],Modifier='SUBTRACT')# Now extract and show the selected points into another datasetExtractSelection()Show()# Clear the selectionClearSelection()
The script starts out by importing functions from the paraview.selection
module. Next, it creates a reference to the active render view and
passes it into the selection functions. The first selection function selects points
visible in the render view within a rectangular region. The rectangle is defined
by bottom left and upper right points, (200, 321) and (600, 744), given in pixel coordinates.
The second selection is of visible points within a polygon defined by the points
(180, 200), (190, 400), and (322, 300). In this call, the selection function
modifies the existing selection so that newly selected points are added to the selection.
This is controlled with the Modifier named function parameter.
Other options for the Modifier parameter are 'SUBTRACT' , 'TOGGLE' ,
and None . When the Modifier is set to None , the previous selection
gets replaced with the new selection. The last call to SelectSurfacePoints
subtracts points from the current selection, which is the combination of the first
two selections.
The last lines in this example script extract the currently selected points from
the currently active source and shows them on the screen. Lastly, the selection
is cleared with the ClearSelection function.
Selections by point or cell ID numbers are also possible, as shown in this example:
fromparaview.selectionimport*# Select cell 1 from all blocks in a multiblock data set on process 0SelectIDs(IDs=[0,1],FieldType='CELL')# Add cell 3 from block 4 on process 0 and cell 5 from block 6 on process 1# to the selectionSelectCompositeDataIDs(IDs=[4,0,3,6,1,5],Modifier='ADD')
Finally, selections by query expressions are also possible via the Python selection API.
As an example, the following selects cells that have the maximum value for
a cell variable named EQPS in the currently active source:
The complete list of selection functions are briefly
described below. For full documentation on these functions, you can invoke the
help function on any of the functions, e.g., help(SelectSurfaceCells) .
SelectSurfacePoints - Select visible points within a rectangular or polygon region.
SelectSurfaceCells - Select visible cells within a rectangular or polygon region.
SelectSurfaceBlocks - Select visible blocks within a rectangular region.
SelectPointsThrough - Select all points within a rectangular region regardless of their visibility.
SelectCellsThrough - Select all cells within a rectangular region regardless of their visibility.
SelectGlobalIDs - Select attributes by global IDs.
SelectPedigreeIDs - Select attributes by Pedigree IDs.
SelectIDs - Select attributes by attribute IDs.
SelectCompositeDataIDs - Select attributes by composite attribute IDs.
SelectHierarchicalDataIDs - Select attributes by hierarchical data IDs.
SelectThresholds - Select attributes in a source by thresholding on values in an associated array.
SelectLocation - Select points by location.
QuerySelect - Selection by query expression.
ClearSelection - Clears the selection on the source passed in as a parameter.
The FindData panel provides easy access to changing the SelectionDisplayProperties for the selection in the active view. The CurrentSelection
section in the FindData dialog shows the selected elements in a spreadsheet
view. You can also make a regular SpreadSheetView do the same by checking
the button in the view toolbar to show only selected elements.
All the types of selections created through mechanisms discussed so far are
transient and primarily used for highlighting data. If you want to do further
operations on the selected subset, such as extract the selected elements and
then save the result out as a new dataset or apply other filters only on the
selected elements, then you need to use one of the extract selection filters.
The ExtractSelection and PlotSelectionOverTime filters fall in
this category of filters.
Properties panel showing the properties for the
ExtractSelection filter.}
The ExtractSelection filter is used to extract the selected elements as a
new dataset for further filtering. There are multiple ways of creating this
filter. You can use the conventional method for creating filters, i.e., using the
Filters menu. When the filter is created, if there is any active
selection, the filter will automatically copy that selection for convenience.
Another way to extract the active selection is using the Extract button
in the FindData panel ( Fig. 6.4).
The Properties panel shows what defines the selection. You can update the
selection by making a new active selection using any of the mechanisms described
earlier in this chapter and then clicking on the CopyActiveSelection
button on the Properties panel for the ExtractSelection filter.
By default, the filter is set up to extract the selected elements alone. This
filter also supports passing the entire input dataset through by simply
marking which elements are selected. For that, check the PreserveTopology
check box on the Properties panel.
PlotSelectionOverTime in action in paraview. The
filter provides a convenient way to plot changes in attributes over time for the
selected set of cells or for points in a temporal dataset.
PlotSelectionOverTime is similar to ExtractSelection in the sense
that it too extracts the selected elements from the input dataset. However,
instead of simply extracting the result, the goal here is to plot attributes at the
selected elements over time.
Fig. 6.7 shows an example use of this filter. In
this case, we wanted to see how the strain (or EQPS) cell attribute
changes over time for two specific cells that we selected in the RenderView using the view-based selection mechanism. The selected cells are the
highlighted elements in the left view. After having selected the cells, we
create the PlotSelectionOverTime filter using the Filters > Data Analysis
menu. (You could also use the
from the DataAnalysis toolbar.) Similar to the ExtractSelection
filter, when this filter is created, it copies the active selection. You can
change it afterwards using the CopyActiveSelection button on the filter’s
Properties panel. On hitting Apply , paraview will show a
visualization similar to the one shown here.
Instead of using the view for defining the selection, you could have used the
FindData panel. In that case, instead of being able to plot each element
over time, you will be plotting summaries for the selected subset over time.
This is essential since the selected subset can have a varying number of
elements over time. The summaries include quantities like mininum, maximum, and
median of available variables. You can make the filter always produce these
statics alone (even when the selection is created by selecting specific elements
in a view) by checking the OnlyReportSelectionStatistics property on the
Properties panel for the PlotSelectionOverTime filter.
When extracting selections, you can use views or the FindData panel to
define the selection. Since the extraction filters are indeed like any other
filters in ParaView, they are re-executed any time the input dataset changes,
properties on the filter change, or the current time changes. Every time the
filter re-executes, it performs the selection and extraction
operations. Thus, if you created the selection using RenderView to create
an id-based selection, the filter will identify which of the elements are of the
requested ids and then pass those. For frustum-based selection, it will
determine what elements fall within the frustum and extract those. Similarly,
with query-based selections created using the FindData panel, the query
is re-evaluated. This can result in the selection of different elements with changes
in timestep. For example, if you are selecting the cells where the strain is
maximum, the selected cell(s) will potentially be different for each time step. Suppose
you want to plot the changes in a cell that has maximum strain at the last
time step – how can we do that? The answer is using the FreezeSelection button on the FindData panel. What that does is convert any
type of selection (frustum, query-based) to an id-based selection matching the
currently selected element ids. Now you can use this frozen, id-based selection
for ExtractSelection or PlotSelectionOverTime.
Saving and combining selections using the Selection Editor panel
Views and FindData panel can be used to create different types of selections.
To save and combine the created selections, you can use the SelectionEditor panel.
This panel can be accessed from the View → Selection Editor.
The SelectionEditor panel can be used to combine selections.
In this example, we are combining frustum, block selector, composite ID and query selections.
The SelectionEditor panel allows you to save selections and combine them using
a boolean expression. This panel shows several pieces of static and user-editable information:
An information-only DataProducer field is set based on the source of the active selection. If the selected object changes, the data producer will change as well, and any saved selections from the previous data producer will be deleted.
An information-only ElementType field (cell or point) that is set based on the element type of the active selection. If a selection is saved and a new active selection is made that has a different element type, ParaView prompts for confirmation to delete all existing saved selections and changes the element type to that of the new active selection.
A user-editable Expression string that defines how to combine the saved selections into a single active selection. This string is automatically filled while adding new selections to the saved selections, meaning that the combined selection will be the union of all saved selections. Selections can be combined using the not (!) operator, or (|) operator, and (&) operator, and xor (^) operator. Parentheses are available to define precedence as well.
A user-editable table lists an automatically assigned name for the selection (s0, s1, s2, etc.), which is used in the Expression property, and the type of the selection. When a selection is highlighted in the saved selections table and ParaView’s active view is a RenderView, the highlighted selection will be shown in that RenderView. When a selection is unhighlighted, it is no longer shown in the RenderView.
Several buttons next to the saved selection table control the addition and removal of selections in
the saved list:
+ (Add Active Selection) button that adds the active selection to the list of saved selections.
- (Remove Selected Selection) button that removes the selected saved selection from the list of saved selections.
X (Remove All Selections) button that removes all saved selections from the list of saved selections.
ActivateCombinedSelections button that sets the combined saved selections as the active selection.
The result of combining the selections as shown in Fig. 6.8.
In ParaView, you can create animations by recording a series of keyframes. At
each keyframe, you set values for the properties of the readers, sources, and
filters that make up the visualization pipeline, as well as the position and
orientation of the camera. Once you have chosen the parameters, you can play
through the animation. When you play the animation, you can cache the geometric
output of the visualization pipeline in memory. When you replay the
animation, playback will be much faster because very little computation must be
done to generate the images. Also, the results of the animation can be saved to
image files (one image per animation frame) or to a movie file. The geometry
rendered at each frame can also be saved in ParaView’s PVD file format, which
can be loaded back into ParaView as a time varying dataset.
AnimationView is the user interface used to create animations by adding
keyframes. It is modeled similar to popular animation and keyframe editing
applications with the ability to create tracks for animating multiple parameters. The
AnimationView is accessible from the View menu.
As seen in Fig. 7.1, this view is presented as a table.
Above the table are controls that administer how time progresses in the
animation. These were discussed briefly in ref{sec:DealingWithTime}.
Within the table, the tracks of the
animation appear as rows, and animation time is presented as increasing from
left-to-right. The first row in the table, simply labeled Time, shows
the total span of time that the animation can cover. The current displayed time
is indicated both in the Time field at the top and with a thick, vertical,
draggable line within the table.
Along the left side of the AnimationView is an expandable list of the
names of the animation tracks (i.e., a particular object and property to
animate). You choose a data source and then a particular property of the data
source in the bottom row. To create an animation track with keyframes for that
property, click the + on the left-hand side; this will create a new track.
In the figure, tracks already exist for SphereSource1’s
PhiResolution property and for the camera’s position. To delete a track, press the
X button. You can temporarily disable a track by unchecking the check box
on the right of the track. To enter values for the property, double-click within
the white area to the right of the track name. This will bring up the
AnimationKeyframes dialog. Double-clicking in the camera entry brings up a
dialog like the one in Fig. 7.2.
From the AnimationKeyframes dialog, you can press New to create new keyframes.
You can also press Delete or DeleteAll to delete some or all of the keyframes. Clicking New will
add a new row to the table. In any row, you can click within the Time column to
choose a particular time for the keyframe, and you can click in the right-hand column to
enter values for the parameter. The exact user interface components that let you
set values for the property at the keyframe time vary. When available, you can
change the interpolation between two keyframes by double-clicking on the central
interpolation column.
Within the tracks of the AnimationView , the place in time where each keyframe
occurs is shown as a vertical line. The values chosen for the property at that
time and the interpolation function used between that value and the next are
shown as text, when appropriate. In the previous figure, for example, the sphere
resolution begins at 10 and then changes to 20, varying by linear interpolation
between them. The camera values are too lengthy to show as text so they are not
displayed in the track, but we can easily see that there are four keyframes
spaced throughout the animation. The vertical lines in the tracks themselves may
be dragged, so you can easily adjust the time at which each keyframe occurs.
Did you know?
You can quickly add a simple animation track and edit the keyframe without using the
AnimationView by using AnimationShortcut .
First, enable ShowAnimationShortcut from
Settings dialog (on the General tab, search for the option by name or switch to advanced view).
Then, several of the animatable properties on the Properties panel will have a icon.
Click this icon to add a new animation track for this property and edit it.
Mode controls the animation playback mode. ParaView supports three modes for playing
animation. In Sequence mode, the animation is played as a sequence of images (or
frames) generated one after the other and rendered in immediate succession. The
number of frames is controlled by the No.Frames spinbox at the end of the
header. Note that the frames are rendered as fast as possible. Thus, the viewing
frame rate depends on the time needed to generate and render each frame.
This is the preferred mode when working with non-temporal data.
|**DEPRECATED**| In RealTime mode, the Duration spinbox (replacing the No.Frames spinbox)
indicates the time in seconds over which the entire animation should run. Each
frame is rendered using the current wall clock time in seconds, relative to the
start time. The animation runs for nearly the number of seconds specified by the
Duration(secs) spinbox. In turn, the number of frames actually generated (or
rendered) depends on the time to generate (or render) each frame.
Note that rendering a scene can be long, so the real time aspect will mostly not work as expected.
It is recommended to use the Sequence mode, and control the frame rate when exporting
as a video.
In SnapToTimeSteps mode, the number of frames in the animation is
determined by the number of time values in the dataset being animated and thus cannot be changed.
This is the animation mode used for ParaView’s default animations: playing through the
time values in a dataset one after the other. Default animations are created by
ParaView when a dataset with time values is loaded; no action is required to
create the animation. Note that using this mode when no time-varying data is
loaded will result in no animation at all.
The Time entry-box shows the current animation time, which is the same as shown by a
vertical marker in this view. You can change the current animation time by
either entering a value in this box, if available, or by dragging the vertical
marker. The StartTime and EndTime entry-boxes display the start and end times
for the animation. By default, when you load time varying datasets, the start
and end times are automatically adjusted to cover the entire time range present
in the data. The lock check-buttons to the right of the StartTime and EndTime
widgets will prevent this from happening, so that you can ensure that your
animation covers a particular time domain of your choosing.
Did you know?
You can change the precision (number of significant digits) displayed by the animation clock
by changing the AnimationTimePrecision value under
Settings/PropertiesPanelOptions/Advanced .
When you load time-varying data, ParaView automatically creates a default
animation that allows you to play through the temporal domain of the data
without manually creating an animation to do so. With the AnimationView , you
can uncouple the data time from the animation time so that you can create
keyframes that manipulate the data time during animation as well.
If you double-click in the TimeKeeper–Time track, the AnimationKeyframes
dialog, an example of which is shown in Fig. 7.4, appears. In this dialog,
you can make data time progress in three fundamentally different ways. If the
AnimationTime radio-button is selected, the data time will be tied to and
scaled with the animation time so that, as the animation progresses, you will see
the data evolve naturally. If you want to ignore the time varying nature of the data,
you can select ConstantTime instead. In this case, you choose a
particular time value at which the data will be displayed for the duration of
the animation. Finally, you can select the VariableTime radio-button to have
full control over data time and to control it as you do any other animatable
property in the visualization pipeline. In the example shown in
Fig. 7.4, time is made to progress forward for the
first 15 frames of the animation, backward for the next 30, and forward
for the final 15.
The following Python commands allow you to get and explore an animation scene.
Just like you can navigate through timesteps in paraview’s user interface, you can use Python commands to do the same.
These commands are available through an animation scene object, retrieved with:
>>> scene=GetAnimationScene()
This object has several methods available to change which animation timestep is shown:
Just like you can change parameters on sources and filters in an animation, you
can also change the camera parameters. As seen in
Fig. 7.6, you can add
animation tracks to animate the camera for all the 3D render views in the setup
separately. To add a camera animation track for a view, with the view selected,
choose Camera from the first drop-down menu. The second drop-down list allows
you to choose how to animate the camera. Then click on the + button.
There are three possible options, each of which provides different mechanisms to specify
the keyframes. It’s not possible to change the mode after the animation track
has been added, but you can simply delete the track and create a new one.
In this mode, you specify camera position, focal point, view angle, and
up direction at each keyframe. The animation player interpolates between these
specified locations. As with other parameters, to edit the keyframes,
double-click on the track. It is also possible to capture the current location
as a keyframe by using the UseCurrent button.
It can be quite challenging to add keyframes correctly and frequently to ensure
that the animation results in a smooth visualization using this mode.
It is the preferred mode if you want a fine control on a few cameras.
The camera customviewpoints can be a great help here.
In this mode, you get the opportunity to specify the path taken by the camera
position and the camera focal point. By default, the path is set up to orbit around
the selected objects. You can then edit the keyframe to change the paths.
This is the preferred mode if you want to control the global motion more than exact
points of view.
Fig. 7.8 shows the dialog for editing these paths for
a keyframe. When Camera Position or Camera Focus is selected, a widget is shown
in the 3D view that can be used to set the path. Use CTRL + LeftClick to
insert new control points, and ⇧ + LeftClick to remove control
points. You can also toggle when the path should be closed or not.
This mode makes it possible to quickly create a camera animation in which the
camera revolves around objects of interest. Clicking on the Orbit button
will pop up a dialog where you can edit the orbit parameters such as the
center of revolution, the normal for the plane of revolution, and the origin (i.e., a
point on the plane where the revolution begins). By default, the Center is the
center of the bounds of the selected objects, the Normal is the current up direction
used by the camera, while the origin is the current camera position.
In this chapter, we will introduce various ways of saving visualization results
in ParaView. Results generated throughout the visualization process not
only include the images and the rendering results, but also include the datasets generated by filters,
the scene representations that will be imported into other rendering applications, and
the movies generated from animations.
You can save the dataset produced by any pipeline module in ParaView, including
sources, readers, and filters. To save the dataset in paraview, begin
by selecting the pipeline module in the Pipeline browser to make it the
active source. For modules with multiple output ports, select the output port
producing the dataset of interest. To save the dataset, use the File > Save Data
menu or the button in the MainControls
toolbar. You can also use the keyboard shortcut CTRL + S (or ⌘ + S).
The SaveFile dialog (Fig. 8.1)
will allow you to select the filename and the file format.
The available list of file formats depends on the type of the dataset you are
trying to save.
On accepting a filename and file format to use, paraview may show
the ConfigureWriter dialog (Fig. 8.2).
This dialog allows you to further customize the
writing process. The properties shown in this dialog depend on the selected file
format and range from enabling you to WriteAllTimeSteps , to selecting
the attributes to write in the output file.
ConfigureWriter dialog in paraview shown when saving a dataset as a csv file.
In pvpython too, you can save the datasets as follows:
# Saving the data using the default properties for# the used writer, if any.>>>SaveData("sample.csv",source)# the second argument is optional, and refers to the pipeline module# to write the data from. If none is specified the active source is used.# To pass parameters to configure the writer>>>SaveData("sample.csv",source,Precision=2,FieldAssociation='Cells')
pvpython will pick a writer based on the file extension and the dataset type
selected for writing, similar to what it does in paraview.
Admittedly, it can be tricky to figure out what options are available for the
writer. The best way is to use the Python tracing capabilities in
paraview and to use the generated sample script as a
reference ( Section 1.6.2).
Make sure you use a similar type of dataset and the same file format as
you want to use in your Python script, when tracing, to avoid runtime issues.
Views that render results (this includes almost all of the views, except
SpreadSheetView ) support saving images (or screenshots) in one of the
standard image formats (PNG, JPEG, TIFF, BMP, PPM).
Certain views also support exportings the results in several formats such as
PDF, X3D, and VRML.
To save the render image from a view in paraview,
use the File > Save Screenshot menu
option. When selected, a file dialog will appear where you can select the file path
and format to which the screenshot should be saved. After selecting the image file, the
SaveScreenshotOptions dialog (Fig. 8.3) will
be shown. This dialog allows you to select various parameters that controls what
image is saved out and how.
The SaveScreenshotOptions dialog, which is used to customize saving screenshots in paraview.
If your visualization setup only has 1 view the active tab, then you’ll be
presented with options shown in
(Fig. 8.3). The available options
are as follows.
ImageResolution : This is the target image resolution in pixels. By
default, it is set to the current view dimensions. You can change it as
needed. If the resolution larger than the current resolution, then ParaView
will use tiling to render the full image in multiple stages. For
reliable results, you may want to present the current aspect ratio. You can
use Tools > Lock View Size Custom to lock the view size to a suitable
aspect ratio.
FontScaling : When a resolution larger than the current resolution
is specified, this allows you to control how the fonts are to be scaled.
Default Scalefontsproportionally tries to achieve WYSIWYG as long as
the aspect ratio is maintained. This is suitable for saving images targeted
for higher DPI (or PPI) display than your screen. Donotscalefonts
may be used to avoid font scaling and keep their size in pixels the same as
what is currently on the screen. This is suitable for saving images targeted
for a larger display with the same pixel resolution.
OverrideColorPalette : Optionally change the color palette just for
saving the screenshot using this drop-down.
StereoMode : This option lets you save the image using one of the
supported stereo modes.
TransparentBackground : If the file format supports it, you can
check this option to save the images with a transparent background rather
than the current background color.
Format : This shows the file format selected in the file save dialog.
For formats that have different options like compression levels, format-specific
options are presented in the SaveScreenshotOptions dialog. The PNG format has
a CompressionLevel option that ranges from 0 (no compression) to 9 (maximum
compression). The JPEG format options are Quality , which ranges from 0 to 100,
and Progressive , which enables saving the file as a progressive JPEG. The TIFF
file format has a Compression option with possible values None , PackBits ,
and Deflate . The BMP file format has no options.
If the active tab has more than one view, then the SaveScreenshotOptions dialog has a few more options as shown in
Fig. 8.4.
Extra options in SaveScreenshotOptions dialog available when the active tab has more than 1 view.
SaveAllViews : Check this to save all the views in the active tab laid
out exactly as in the UI. If unchecked, only the active view will be saved.
SeparatorOptions : These control the separator drawn between the views in the
generated image. You can specify the SeparatorWidth in approximate pixels
as well as the SeparatorColor .
To save a screenshot in pvpython, you use SaveScreenshot .
# Save a screenshot from a specific view.>>>myview=GetActiveView()>>>SaveScreenshot("aview.png",myview)# Save all views in a tab>>>layout=GetLayout()>>>SaveScreenshot("allviews.png",layout)# To save a specific target resolution, rather than using the# the current view (or layout) size, and override the color palette.>>>SaveScreenshot("aviewResolution.png",myview,ImageResolution=[1500,1500],OverrideColorPalette="Black Background")
As always, you can use Python tracing in paraview to trace
the exact form of the method to use to save a specific screenshot image.
When available, you can export a visualization in a view in several of the
supported formats using the File > Export View menu option in
paraview. For a
RenderView (or similar), the available formats include Cinema Database,
EPS, PDF, PS, SVG, POV, VRML, WebGL, X3D, and X3DB. On selecting a file
as which to export, paraview may pop up an ExportOptions dialog that
allows you to set up parameters for the exporter, similar to saving datasets
( Section 8.1).
In addition, from pvpython, exporting takes the following form (again,
just use Python trace to figure out the proper form – that’s the
easiest way).
>>> myview=GetActiveView()>>> ExportView('/tmp/sample.svg',view=myview, Plottitle='ParaView GL2PS Export', Compressoutputfile=1)# the arguments after 'view' depend on the exporter selected.
The SaveAnimationOptions dialog in paraview, which is used to customize saving of animation.
To save an animation as a series of images or a video file, you use the
File > Save Animation menu option. This pops up a file save dialog where you choose
where to save the file and which format to use. After selecting the file and format, the SaveAnimationOptions
dialog (Fig. 8.5) is display. This dialog is nearly a clone of the
SaveScreenshotOptions dialog (Fig. 8.3), including,
optionally, the extra multiview options from Fig. 8.4,
with additional format-specific compression options and a few animation-specific parameters.
These are as follows:
FrameRate : When saving the animation as a video file (AVI or Ogg) rather than
a series of images, this lets you specify the frame rate for the generated video. It has
no effect when saving as a series of images.
FrameWindow : If you didn’t want to save out the full animation, instead limit to
a specific window, you can use this to specify the range of frames to save. If you are generating
a animation from a temporal dataset with timesteps, the frame generally corresponds to the
timestep number.
On accepting this dialog, you will be able to choose the output file location
and format. The available file formats include AVI and Ogg (when available)
video formats, as well as image formats such PNG, JPEG, and TIFF. If saving as
images, ParaView will generate a series of image files sequentially numbered
using the frame number as a suffix to the specified filename.
To save animations in pvpython, you use SaveAnimation . The arguments to this function are
same as the SaveScreenshot with additional parameters for the animation specific options.
Besides saving the results produced by your visualization setup, you can save
the state of the visualization pipeline itself, including all the pipeline
modules, views, their layout, and their properties. This is referred to as the
ApplicationState , or just
State . In paraview, you can save the
state using the File > Save State… menu option. Conversely, to load a saved
state file, you can use File > Load State….
There are two types of state files that you can save in paraview:
ParaView state file (*.pvsm) and Python state file (*.py). The
PVSM files are XML-based text files that are human and machine readable,
although not necessarily human friendly for a novice user. However, if you don’t
plan to read and make sense of the state files, PVSM is the most robust and
reliable way to save the application state. For those who want to save the state and then
modify it manually, using Python state files may be better, as using
Python trace simply traces the actions that you perform in the UI as a
Python script. Python state files, on the other hand, save the entire current state of the
application as a Python script that you can use in paraview or the
PythonShell .
To load a state file, you use the File > Load State… menu.
Note that loading a state file will affect the current visualization state.
The LoadStateOptions dialog in paraview showing the options for where to find data files.
If you load a PVSM file this way you will be asked where
to search for the data files. There are three available options: UseFileNamesFromState , Searchfilesunderspecifieddirectory and ChooseFileNames . If you select UseFileNamesFromState then ParaView will
look for the data at the absolute paths saved in the state file. If you select Searchfilesunderspecifieddirectory then you will see an option to browse for a directory that ParaView will search for the files before
looking for them in the absolute path in the state file. This defaults to the
location of the state file to make sharing state files between computers easier. If you select
ChooseFileNames then you will be given a list of file names in the state file and can override
each one individually.
The LoadStateOptions dialog in paraview showing the Searchfilesunderspecifieddirectory option.
You can save/load the PVSM state file in pvpython as follows:
>>> fromparaview.simpleimport*# Save the PVSM state file. Currently, this doesn't support# saving Python state files.>>> SaveState("sample.pvsm")# To load a PVSM state file.>>> LoadState("sample.pvsm")
To replace all data files used by state with those under a specific directory,
you use the following form:
The function signature can become a little more complex if you want to
explicitly override filenames used in the state file. It may be easier to use
the Python trace capabilities to generate the function call for specific state
files. It takes the following form:
>>> LoadState("sample.pvsm", filenames = [ # a `dict` object for each reader in statefile to update. { "name": "[reader name as shown in the pipeline browser]", # if multiple readers have the same name, 'id' may be used # instead of 'name' where the value is "id" used in the # state file for this reader. # filename properties and their overridden values for this # reader, for example: "FileName" : "foo.vtk", }, # multiple such `dict`s can be specified. ])# here's an example>>> LoadState(statefile, filenames=[ { 'name' : 'can.ex2', 'FileName' : data_dir + 'can.ex2', }, { 'name' : 'dataset', 'FileName' : data_dir + 'disk_out_ref.ex2', }, { 'name' : 'timeseries', 'FileName' : [ data_dir + 'dualSphereAnimation/dualSphereAnimation_P00T0000.vtp', data_dir + 'dualSphereAnimation/dualSphereAnimation_P00T0001.vtp', data_dir + 'dualSphereAnimation/dualSphereAnimation_P00T0002.vtp', data_dir + 'dualSphereAnimation/dualSphereAnimation_P00T0003.vtp', data_dir + 'dualSphereAnimation/dualSphereAnimation_P00T0004.vtp', data_dir + 'dualSphereAnimation/dualSphereAnimation_P00T0005.vtp', data_dir + 'dualSphereAnimation/dualSphereAnimation_P00T0006.vtp', data_dir + 'dualSphereAnimation/dualSphereAnimation_P00T0007.vtp', data_dir + 'dualSphereAnimation/dualSphereAnimation_P00T0008.vtp', data_dir + 'dualSphereAnimation/dualSphereAnimation_P00T0009.vtp', data_dir + 'dualSphereAnimation/dualSphereAnimation_P00T0010.vtp'] }, ])
Section 8.1 and Section 8.2 are two
ways of saving datasets and images using actions, i.e., you click a button (or in
Python, invoke a function) and the results are saved out immediately. If, for
example, you now want to generate the results for another timestep, you have to
repeat all the actions. One way to avoid this is to put together a Python script
to generate the data and image files and then use that as a macro. An easier
way is to use extractors .
Extractors are a type of pipeline
module, similar to sources and filters, but behave more like writers.
Similar to filters, they have inputs, unlike sources or filters, however, they
produce no output that can be consumed by another pipeline module. Instead,
when activated, they generate files – which we call extracts.
Since they are just another pipeline module, you use similar mechanisms
as sources and filters for creating and configuring these.
You use the Extractors menu to create them.
The PipelineBrowser shows all the extractors present
in the visualization.
You select one of them by clicking on it in the PipelineBrowser
at which point the Properties panel will update to show parameters on
the selected extractor.
There are two types of extractors: data extractors and image
extractors. The former generate files from datasets produced by sources
and filters, while the latter save out rendering results from views. When
created, a data extractor by default uses the active source as the input
(similar to filters) which an image extractor uses the active view
instead.
Properties panel showing properties on an image extracts generator for PNG
files.
You use the Properties panel view and change extractor properties.
The available properties can be grouped into two major groups: first are
Trigger properties which are common to all extractors, and the second
are the Writer properties which are parameters specific to type of writer
the extractor uses.
Trigger properties define when the extractor
is activated i.e.
under what conditions does the extractor produce extracts. Currently, we
support time-based controls. You can select the
StartTimeStep ,
EndTimeStep or the
Frequency at which to generate the results.
Frequency is the number of timesteps per activation thus to write every
other timestep, set the Frequency to 2, to write every 3rd timestep, set it
to 3, and so on.
Writer properties are specific to the writer. For data extractors,
these will be similar to the writer properties shown in the
ConfigureWriter dialog for the writer described
in Section Section 8.1. For
image extractors, they are similar to the SaveScreenshotOptions
dialog described in Section Section 8.2.1. The Writer
properties also lets you set a FileName . This is the file name to use to
save the extracts. Since extractors are designed to generate a new
extract every time they are activated, the FileName supports patterns that
let you make the filename unique per activation. {timestep} or {time} in the
filename are replaced by the timestep index and the time value for each
activation. You add leading zeros (or other prefixes) to the numbers using a
form such as {timestep:06d}. There the timestep will be padded with zeros if the
number of digits is less than 6. You should not use absolute paths for
specifying the filenames here. We will see how to select prefix to store these
extracts under in the next section.
SaveExtractsOptions dialog shown on File > Save Extracts….
Once the extractors have been setup, you can trigger the saving of
extract using File > Save Extracts…. This will pop up the
SaveExtractOptions dialog which lets you configure the extract generation.
ExtractsOutputDirectory specifies the root directories under which all extracts are saved.
Check GenerateCinemaSpecification to generate a data.csv file under the chosen
extracts output directory that summarizes the generated extracts. This can be then used
with viewers provided by
the Cinema Science project to explore the generated extracts.
Hit Ok and ParaView will animate through all timesteps
(similar to using the VCRControls), activating extractors based
on their trigger criteria and then generating extracts. On successful
completion you should have files under the chosen root directories.
PythonStateOptions dialog shown when saving a Python state file using
File > Save State.
In addition to generating extracts using the GUI, you can use pvpython or pvbatch
to generate extract offline. Thus is especially handy for HPC use-cases; you can
setup your state using an interactive session and once done save out the state and
schedule a non-interactive job for the potentially time-consuming extract generation
stage. To do so, setup your visualization pipeline including the extractors
as normal. Then, instead of using SaveExtracts , use
File > Save State…` and save out a Python state file.
The PythonStateOptions dialog has a section similar to SaveExtractsOptions
dialog for choosing ExtractsOutputDirectory and GenerateCinemaSpecification.
Click Ok to save the Python script. The Python script has a section near
the end of the end as follows:
The Properties panel is perhaps the most often used panel in
paraview. This is the panel you would use to change properties
on modules in the visualization pipeline, including sources and filters, to control how
they are displayed in views using the Display properties, and
to customize the view itself. In this chapter, we take a closer look at the
Properties panel to understand how it works.
Before we start dissecting the Properties , remember that the Properties
panel works on active objects, i.e., it shows the properties for the active
source and active view, as well as the display properties, if any, for active source in the active view.
Fig. 1.8 shows the various parts of the
Properties panel. At the top is the group of buttons that let you accept,
reject your changes to the panel or Delete the active source.
Did you know?
You can delete multiple sources by selecting them using the
CTRL (or ⌘) key when selecting in the PipelineBrowser and then clicking on the Delete button.
Sometimes, the Delete button may be disabled. That happens when the
selected source(s) have other filters connected to them. You will need to
delete those filters first.
The Search box allows you to search for a property by using the name or the
label for the property. Simply start typing text in the Search box, and the
panel will update to show widgets for the properties matching the text.
The Properties panel has two modes that control the verbosity of the panel:
default and advanced. In the default mode, a smaller subset of the available
properties is shown. These are generally the frequently used properties for the
pipeline modules. In advanced mode, you can see all the available properties.
You can toggle between default and advanced modes using the
button next the Search box.
When you start searching for a property by typing text in the Search box,
irrespective of the current mode of the panel (i.e., default or advanced), all
properties that match the search text will be shown.
Did you know?
The Search box is a recurring widget in paraview. Several other panels
and dialog boxes, including the Settings dialog and the ColorMapEditor ,
show a similar widget. Its behavior is also exactly the same as in the case of the
Properties panel. Don’t forget that the
button can be used to toggle between default and advanced modes.
The Properties , Display , and View sections in the panel
show widgets for properties on the active source, its display
properties in the active view, and the properties for the active view,
respectively. You can collapse/expand each of these sections by
clicking on the section name.
To the right of each section name is a set of four buttons. Clicking the
copies the current set of property values to the
clipboard while clicking the will paste those
property values into another compatible panel section. Note that the paste icon
is enabled only for panel sections where the copied properties can be pasted.
The next two buttons and
enable customizing the default values
used for those properties. Refer to Section 12.2
to learn more about customizing default property values.
Options for customizing the Properties panel layout using the
Settings (left). View properties in a separate dock panel (right).
The Properties panel, by default, is set up to show the source, display, and
view properties on the same panel. You may, however, prefer to have each of these
sections in a separate dockable panel. You can indeed do so using the
Settings dialog accessible from the Edit > Settings menu.
On the General tab search of the propertiespanel using the
Search box, you should see the setting that lets you pick whether to
combine all the sections in one (default), to separate out either the
Display or View
sections in a panel, or to create separate panels
for each of the sections. You will need to restart paraview for
this change to take effect. Also, since the Apply and Reset buttons only
apply to the Properties section, they will only be shown in the dock panel
that houses it.
When visualizing any data it is important to control how the data is actually rendered.
Most of the properties controlling the appearance of an object can be found in the DisplayProperties section in the object inspector (see section display properties).
This chapter tries to entirely cover the lighting properties of an object when using the Surface representation.
These lighting models are intended to be easy-to-use basic models for general visualisation purposes.
Both of these models are mainly controlled by the same parameters.
The only difference between the two is that the flat shading model does not interpolate the normals of the rendered surfaces,
meaning that a Gouraud lighting with no normal array will produce the same result as the flat shading model.
The parameters for these two models are :
Specular: how specular the object is, that is how much of the light it will reflect.
Specular Color: the color of the resulting specular.
Specular Power: how much the specular is spread on the object. The lower the wider it spreads.
Luminosity: how much light the object emits. Only takes effect with a pathtracer backend.
Ambient: coefficient for the ambient lighting.
Diffuse: coefficient for the diffuse lighting.
Texture Coordinates: the texture coordinates to use when applying a texture. This is needed to be able to use the Texture property.
Texture: also called albedo, this is the perceived color of the object.
Show Texture On Backface: whether or not to show the texture on the backface of the surface.
Flip Texture: if on, flip the color texture.
Some other properties specific to the Gouraud shading :
Normal Array: what array to use as the normal array
Tangent Array: what array to use as the tangent array. Only needed when using the Normal Texture.
Normal Texture: a normal map. This allows to have more precise shading without the need to subdivide the geometry. Stores the normal direction {x,y,z} in the RGB channels.
This lighting model is more complex than the previous ones but allows a wider range of effect on the objects
and a more realistic rendering. Since this model is more complex to grasp, several blog posts have been written to
explain how to use it (links to blogs are provided in the relevant sections below).
Basic parameters for this model are :
Metallic: whether the object is metallic (= 1.0) or non-metallic / dielectric (= 0.0). For most materials, the value is either 0.0 or 1.0 but any value in between is valid.
Roughness: parameter used to specify how glossy an object is.
Luminosity: how much light the object emits. Only takes effect with a pathtracer backend.
Diffuse: the global amount of light reflected by the object. Should usually be set to 1.0 as it is not an actual parameter of the theorical PBR shading model but it can be used for artistic effects.
Following are more advanced properties. They can be hard to understand visually without knowing the theory behind it so
it is advised to refer to the linked blog posts when using them for the first time.
Anisotropy: the strength of the anisotropy (between 0.0 and 1.0). 0.0 means an isotropic material, 1.0 means a fully anisotropic material.
Anisotropy Rotation: rotates the direction of the anisotropy (ie. the tangent) around the normal counter-clockwise (between 0.0 and 1.0). A value of 1.0 corresponds to a rotation of 2 * PI.
anisotropy parameters are fully detailed here: anisotropy blog
Coat Strength: the strength of the coat layer, between 0.0 and 1.0. 0 means no clear coat. This parameter can be considered as the thickness of the coating.
Coat Roughness: the roughness of the coat layer.
Coat Color: the color of the coat layer. Specular reflections on the coat layer are always white, but this parameter modifies the radiance that passes through it.
Base IOR: the refractive index of the base layer.
Coat IOR: the refractive index of the coat layer.
Edge Tint: the color of the reflection on the edges at grazing angles for a metallic material.
Finally, some parameters can also be mapped using textures.
As in the Gouraud shading model, a proper value for the Texture Coordinates and Normal Array properties will be needed in order to apply textures.
Base Color Texture: also called albedo, this is the perceived color of the object, the diffuse color for non-metallic objects or the specular color for metallic objects.
Normal Texture: a normal map. This allows to have more precise shading without the need to subdivide the geometry. Stores the normal direction {x,y,z} in the RGB channels.
Material Texture: ambient Occlusion/Roughness/Metallic factors on the Red/Green/Blue channels. Also called ORM texture.
Coat Normal Texture: a normal map for the clear coat layer.
Anisotropy Texture: texture that controls the anisotropy strength on the red channel, while the green channel holds the anisotropy rotation. The blue channel is discarded.
Emissive Texture: for light-emitting texture. Note that the material will not actually emit light, and the texture is ignored by OSPRay and NVidia pathtracing backends.
One of the first things that any visualization tool user does when
opening a new dataset and looking at the mesh is to color the mesh with some
scalar data. Color mapping is a common visualization technique that maps data to
color, and displays the colors in the rendered image. Of course, to map the
data array to colors, we use a transfer function. A transfer function can also
be used to map the data array to opacity for rendering translucent surfaces or
for volume rendering. This chapter describes the basics of mapping data arrays to
color and opacity.
Color mapping (which often also includes opacity mapping) goes by various names
including scalar mapping and pseudo-coloring. The basic principle entails
mapping data arrays to colors when rendering surface meshes or volumes. Since
data arrays can have arbitrary values and types, you may want to define to which
color a particular data value maps. This mapping is defined using what are
called color maps or transfer functions. Since such mapping from
data values to rendering primitives can be defined for not just colors, but
opacity values as well, we will use the more generic term transfer functions.
Of course, there are cases when your data arrays indeed specify the
red-green-blue color values to use when rendering (i.e., not using a transfer
function at all). This can controlled using the MapScalars display property.
Refer to Chapter Section 4.3 for details. This
chapter relates to cases when MapScalars is enabled, i.e., when the transfer
function is being used to map arrays to colors and/or opacity.
In ParaView, you can set up a transfer function for each data array
for both color and opacity separately. ParaView associates a transfer function
with the data array identified by its name. The same transfer function is used
when coloring with the same array in different 3D views or results from
different stages in the pipeline. You can also use Section 3.2.1
to have independant color map by array name and representation.
For arrays with more than one component, such as vectors or tensors, you can
specify whether to use the magnitude or a specific component for the
color/opacity mapping. Similar to the transfer functions themselves, this
selection of how to map a multi-component array to colors is also associated
with the array name. Thus, two pipeline modules being colored with the arrays
that have the same name will not only be using the same transfer functions for
opacity and color, but also the component/magnitude selection.
Common Errors
Beginners find it easy to forget that the transfer function is associated with
an array name and, hence, are surprised when changing the transfer function for
a dataset being shown in one view affects other views as well. Using different
transfer functions for the same variable is discouraged by design in ParaView,
since it can lead to the misinterpretation of values. If you want to use different
transfer functions, despite this caveat, you can use the Separate Color Map feature
(see Section 3.2.1).
There are separate transfer functions for color and opacity. The opacity
transfer function is used for volume rendering, and it is optional when used for surface
renderings.
The controls used for selecting the array to color within the
Properties panel (top) and the ActiveVariablesControls toolbar (bottom).
You can pick an array to use for color mapping, using either the Properties
panel or the ActiveVariablesControls toolbar. You first select the array
with which to color and then select the component or magnitude for multi-component
arrays. ParaView will either use an existing transfer function or create a new
one for the selected array.
Here’s a sample script for coloring using a data array from the
disk_out_ref.ex2 dataset.
fromparaview.simpleimport*# create a new 'ExodusIIReader'reader=ExodusIIReader(FileName=['disk_out_ref.ex2'])reader.PointVariables=['V']reader.ElementBlocks=['Unnamed block ID: 1 Type: HEX8']# show data in viewdisplay=Show(reader)# set scalar coloringColorBy(display,('POINTS','V'))# rescale color and/or opacity maps used to include current data rangedisplay.RescaleTransferFunctionToDataRange(True)
The ColorBy function provided by the simple module ensures that the color
and opacity transfer functions are set up correctly for the selected array, which
is using an existing one already associated with the array name or is creating a
new one. Passing None as the second argument to ColorBy will
display scalar coloring.
ColorMapEditor panel in paraview showing the major components of the panel.
In paraview, you use the ColorMapEditor to customize the
color and opacity transfer functions. You can toggle the ColorMapEditor
visibility using the View > Color Map Editor menu option.
As shown in Fig. 3.18, the panel follows a layout
similar to the Properties panel. The panel shows the properties for the
transfer function, if any, used for coloring the active data source (or filter)
in the active view. If the active source if not visible in the active view, or
is not employing scalar coloring, then the panel will be empty.
Similar to the Properties panel, by default, the commonly used properties are
shown. You can toggle the visibility of advanced properties by using the
button. Additionally, you can search for a
particular property by typing its name in the Search box.
Whenever the transfer function is changed, we need to re-render, which may be
time consuming. By default, the panel requests a render on every change. To avoid
this, you can toggle the button. When unchecked,
you will need to manually update the panel using the RenderViews button.
The button restores the application
default settings for the current color map.
The and
buttons save the current color and opacity transfer function, with all
its properties, as the default transfer function. ParaView will use
it next time it needs to set up a transfer function to color a new data
array. The button saves the transfer
function as default for an array of the same name while the
button saves the transfer function as
default for all arrays. Note that this will not affect transfer
functions already setup. Also this is saved across sessions,
so ParaView will remember this even after restart.
In order to force ParaView to use a separate color map on the current Active Representation,
click on the button shown in Fig. 3.19. A separate color map
is not shared across representations by name, but is instead uniquely associated with the array
name and the representation.
This can also easily be done in Python:
fromparaview.simpleimport*Wavelet()wavelet1Display=Show()wavelet1Display.SetRepresentationType('Surface')# set scalar coloringColorBy(wavelet1Display,'RTData')# set the usage of a Separate Color Mapwavelet1Display.UseSeparateColorMap=True# or use the ColorBy interface directlyColorBy(wavelet1Display,'RTData',separate=True)# display the same data in another view for comparison with different color map# get layoutlayout1=GetLayout()# split celllayout1.SplitHorizontal(0,0.5)renderView1=GetActiveView()# Create a new 'Render View'renderView2=CreateView('RenderView')# place view in the layoutlayout1.AssignView(2,renderView2)# set active viewSetActiveView(renderView2)wavelet2Display=Show()wavelet2Display.SetRepresentationType('Surface')# Use the ColorBy interface to create a separated color mapColorBy(wavelet2Display,'RTData',separate=True)# get separate color transfer function/color map for 'RTData'separate_wavelet2Display_RTDataLUT=GetColorTransferFunction('RTData',wavelet2Display,separate=True)# Apply a preset using its name.separate_wavelet2Display_RTDataLUT.ApplyPreset('Cold and Hot',True)ResetCamera(renderView1)ResetCamera(renderView2)RenderAllViews()
The MappingData group of properties controls how the data is mapped to
colors or opacity. The transfer function editor widgets are used to control the
transfer function for color and opacity. The panel always shows both the
transfer functions. Whether the opacity transfer function gets used depends on
several things:
When doing surface mesh rendering, it will be used only if
Enableopacitymappingforsurfaces is checked
When doing volume rendering, the opacity mapping will always be used.
To map the data to color using a log scale, rather than a linear scale, check
the Uselogscalewhenmappingdatatocolors . It is assumed that the data
is in the non-zero, positive range. ParaView will report errors and try to
automatically fix the range if it is ever invalid for log mapping.
The range of a color map is a very important property that controls the mapping
of data values to colors. The range can be automatically updated in a number
of situations for convenience. How the range is updated is controlled by the
AutomaticRescaleRangeMode property in the ColorMapEditor . When
Never is selected, the data range will never be updated automatically. When
Growandupdateon'Apply' is selected, ParaView will grow the color/opacity
map range to include the current data range every time you hit Apply on the
Properties panel. Thus, when the data range changes, if the timestep is changed,
the color/opacity map range won’t be affected. To grow the range on change in
timestep as well, use the Growandupdateeverytimestep option. Now the
range will be updated on Apply as well as when the timestep changes.
Grow indicates that the color/opacity map range will only be increased,
never shrunk, to include the current data range. If you want the range to
match the current data range exactly, then you should use the Clampandupdateeverytimestep option. Now the range will be clamped to the exact data
range each time you hit Apply on the Properties panel or when the
timestep changes. The initial value for the AutomaticRescaleRangeMode
is controlled by the General setting TransferFunctionResetMode in the
Settings dialog (see Section 12.1.1 ).
Using the transfer function editors is pretty straightforward. Control points
in the opacity editor widget and the color editor widget are independent of each
other. To select a control point, click on it. When selected, the control point
is highlighted with a red circle and data value associated with the control
point is shown in the Data input box under the widget. Clicking in an empty area
will add a control point at that location. To move a control point, click on the
control point and drag it. You can fine tune the data value associated with the
selected control point using the Data input box. To delete a control point,
select the control point and then type the Delete key. Note that the mouse pointer
should be within the transfer function widget. While the end control points cannot be moved or
deleted, if you drag the bars at either end, you can change the range of the transfer
function. You can also rescale the entire transfer function to move the control
points, as is explained later.
In the opacity transfer function widget, you can move the control points
vertically to control the opacity value associated with that control point. In
the color transfer function widget, you can select the control point and then type the
Enter or Return key to pop up a color chooser dialog to set the color associated
with that control point.
The opacity transfer function widget also offers some control over the
interpolation between the control points. Double click on a control point to
show the interpolation control widget, which allows for changing the sharpness and
midpoint that affect the interpolation. Click and drag the control handles to
see the change in interpolation.
The combo box at the top of the transfer function editor is used to quickly switch between the
“Default” presets. Which presets are default ones can be configured from the ColorPreset
manager, which can be accessed with the Favorites button described later.
The several control buttons on the right side of the transfer function widgets
support the following actions:
: Rescales the color and opacity transfer
functions using the data range from the data source selected in the Pipeline
browser, i.e., the active source. This rescales the entire transfer function.
Thus, all control points including the intermediate ones are proportionally
adjusted to fit the new range.
: Rescales the color and opacity transfer
functions using a range provided by the user. A dialog will be popped up for
the user to enter the custom range.
: Rescales the color and
opacity transfer functions to the range of values for data over all
timesteps. This operation may be costly as data for all timesteps
needs to be read.
: Rescales the color
and opacity transfer functions using the range of values for the
elements (cells or points) visible in the view. This operations
assigns the entire range of colors to visible elements which may
reveal patterns not visible otherwise.
: Inverts the color transfer function
by moving the control points, e.g,. a red-to-green transfer function will be
inverted to a green-to-red one. This only affects the color transfer function and
leaves the opacity transfer function untouched.
: Loads the color transfer function
from a preset. The ColorPreset manager dialog pops up to enable you to choose
one of the color maps included with ParaView or import presets from a file.
: Saves the current color transfer
function to presets. The ColorPreset manager dialog pops up to let you
name the transfer function and export the transfer function to a file. The
opacity function can also be saved with the transfer function. The preset will
be added under the Default and User groups.
: This toggles the detailed view for the
transfer function control points. This is useful to manually enter values for
the control points rather than using the UI.
Color Mapping Parameters, including advanced properties. Advanced
properties are enabled by clicking the gear icon at the top right of the
ColorMapEditor (not shown).}
The ColorMappingParameters group of properties provides additional
control over the color transfer function, including control over the color
interpolation space, which is either RGB, HSV, Lab, Diverging, or Lab/CIEDE2000.
To color data values falling below or above the range of the color map with special colors, enable the
advanced UseBelowRangeColor and UseAboveRangeColor options,
respectively. You can choose different colors for data falling on either side of
the range. When color mapping floating point arrays with NaNs, you can select
the color and opacity to use for NaN values. You can also affect whether the color transfer
function uses smooth interpolation or discretizes the map into a fixed
number of colors.
In pvpython, you control the transfer functions by getting access
to the transfer function objects and then changing properties on those. The
following script shows how you can access transfer functions objects.
fromparaview.simpleimport*# You can access the color and opacity transfer functions# for a particular array as follows. These functions will# create new transfer functions if none exist.# The argument is the array name used to locate the transfer# functions.>>>colorMap=GetColorTransferFunction('Temp')>>>opacityMap=GetOpacityTransferFunction('Temp')
Once you have access to the color and opacity transfer functions, you can change
properties on these similar to other sources, views, etc. Using the Python
tracing capabilities to discover this API is highly recommended.
# Rescale transfer functions to a specific range>>>colorMap.RescaleTransferFunction(1.0,19.9495)>>>opacityMap.RescaleTransferFunction(1.0,19.9495)# Invert the color map.>>>colorMap.InvertTransferFunction()# Map color map to log-scale preserving relative positions for# control points>>>colorMap.MapControlPointsToLogSpace()>>>colorMap.UseLogScale=1# Return back to linear space.>>>colorMap.MapControlPointsToLinearSpace()>>>colorMap.UseLogScale=0# Change using of opacity mapping for surfaces>>>colorMap.EnableOpacityMapping=1# Explicitly specify color map control points# The value is a flattened list of tuples# (data-value, red, green, blue). The color components# must be in the range [0.0, 1.0]>>>colorMap.RGBPoints=[1.0,0.705,0.015,0.149,5.0,0.865,0.865,0.865,10.0,0.627,0.749,1.0,19.9495,0.231373,0.298039,0.752941]# Similarly, for opacity map. The value here is# a flattened list of (data-value, opacity, mid-point, sharpness)>>>opacity.Points=[1.0,0.0,0.5,0.0,9.0,0.404,0.5,0.0,19.9495,1.0,0.5,0.0]# Note, in both these cases the controls points are assumed to be sorted# based on the data values. Also, not setting the first and last# control point to have same data value can have unexpected artifacts# in the 'Color Map Editor' panel.
Oftentimes, you want to rescale the color and opacity maps to fit the
current data ranges. You can do this as follows:
>>> source=GetActiveSource()# Update the pipeline, if it hasn't been updated already.>>> source.UpdatePipeline()# First, locate the display properties for the source of interest.>>> display=GetDisplayProperties()# Reset the color and opacity maps currently used by 'display' to# use the range for the array 'display' is using for color mapping.# This requires that the 'display' has been set to use scalar coloring# using an array that is available in the data generated. If not, you will# get errors.>>> display.RescaleTransferFunctionToDataRange()
The color legend, also known as scalar bar or color bar, is designed to provide
the user information about which color corresponds to what data value in the
rendered view. You can toggle the visibility of the color legend corresponding
to the transfer function being shown/edit in the ColorMapEditor by using the
button near the top of
the panel. This button affects the visibility of the legend in the active view.
Fig. 3.22 shows the various components of the color
legend. By default, the title is typically the name of the array (and component
number or magnitude for non-scalar data arrays) being mapped. Automatically generated
labels appear on one side of the color legend, while on the other side are annotations,
optionally including start and end annotations depicting the minimum and maximum
of the color legend range.
The color legend can be manipulated with the mouse. You can click and drag the legend to place it
at any position in the view. Additionally, you can change the length of the legend
by clicking and dragging the end-markers shown when you hover the mouse
pointer over the legend.
You can edit the color legend parameters by clicking on the
button on the ColorMapEditor panel. This
will pop up the EditColorLegendProperties dialog that shows the available
parameters. Any changes made will affect only the particular color legend in
the active view.
The first few options in the EditColorLegendProperties control the
orientation and location of the color legend in the render view. AutoOrient turns on automatic determination of the color legend’s orientation. The
color legend will change orientation to horizontal when it is dragged to the
bottom or the top of the render view, and it will change to vertical when it is
dragged to the left or right side. When disabled, you can choose the orientation
you want the color legend to have by choosing an option in the Orientation
combo-box. The WindowLocation option controls the location of the color legend in
the window; if the value AnyLocation is selected, then the color
legend will not be forced into any particular position. The color legend can be
positioned by clicking and dragging it with the mouse in the render view,
or the Position property can be specified explicitly with
fractional coordinates that range from [0, 1] and represent the fraction of the window
width (or height) where the color legend’s bottom left corner should be placed. Note
that if the color legend is placed interactively with the mouse, the WindowLocation option
will automatically change to AnyLocation .
Besides the obvious changing of title text and font properties for the title,
labels, and annotations, there are some other parameters that control the
appearance of the color legend.
By default, the title is rotated 90 degrees counter-clockwise when the legend
is oriented vertically to better align with the legend. Checking the
HorizontalTitle box forces the title of the color legend to be horizontal
regardless of color legend orientation.
DrawAnnotations determines whether the annotations
(including the start and end annotations) are to be drawn at all.
When checked, DrawNanAnnotation results in the color legend showing the
NaN color set in the ColorMapEditor panel in a separate color box right beside the
color legend. The annotation text shown for that box can be modified by changing
the NanAnnotation text.
If AutomaticLabelFormat is checked, ParaView will try to pick an optimal
representation for numerical values based on the value and available screen
space. By unchecking it, you can explicitly specify the printf-style
format to use for numeric values. To explicitly label values of interest, enable
the UseCustomLabels option. You can specify exactly the labeled values
you wish to display in the table that appears when this option is chosen.
ColorBarThickness is used to control the thickness of the legend. It is
defined in terms of points just like how font sizes are specified. Use ColorBarLength to explicitly set the length of the color bar. This property is defined
as a fraction in the range [0, 1] of the window width (when the color legend is
oriented horizontally) or height (when oriented vertically).
To show the color legend or scalar bar for the transfer function used for scalar
mapping a source in a view, you can use API on its display properties:
>>> source=...>>> display=GetDisplayProperties(source,view)# to show the color legend>>> display.SetScalarBarVisibility(view,True)# to hide the same>>> display.SetScalarBarVisibility(view,False)
To change the color legend properties as in
Section 3.4.1, you need to first get access to the
color legend object for the color transfer function in a particular view. These
are analogous to display properties for a source in a view.
>>> colorMap=GetColorTransferFunction('Temp')# get the scalar bar in a view (akin to GetDisplayProperties)>>> scalarBar=GetScalarBar(colorMap,view)# Now, you can change properties on the scalar bar object.>>> scalarBar.TitleFontSize=8>>> scalarBar.DrawNanAnnotation=1
Simply put, annotations allow users to put custom text at particular data values
in the color legend. The min and max data mapped value annotations are
automatically added. To add any other custom annotations, you can use the
ColorMapEditor .
Since the list of annotations is an advanced property, you need to either toggle the
visibility of advanced properties using the icon
near the top of the panel or type annotations in the
search box. That will show the Annotations widget, which is basically a
list widget where users can enter key-value pairs, rather than value-annotation
pairs, as shown in Fig. 3.25.
Widget to add/edit annotations on the ColorMapEditor panel
You can use the buttons of the right on the widget to add/remove entries. Enter
the data value to annotate under the Value column and then enter the text to
display at that value under the Annotation column.
You can use the Tab↹ (tab) key to edit the next entry. Hitting Tab↹ after
editing the last entry in the table will automatically result in adding a new
row, thus, making it easier to add bunch of annotations without having to click
any buttons.
Some annotation texts may not show up on the legend. There are two possible reasons
an annotation may not be shown. First, the value added is outside the mapped range of the color transfer
function. Second, DrawAnnotations is unchecked in the ColorLegendParametersdialog .
The and buttons can be used to fill the
annotations widget with unique discrete values from a data array, if
possible. Based on the number of distinct values present in the data
array, this may not yield any result (Instead, a warning message will
be shown). The data array values come either from the selected source object
if you use the button or it comes from
the visible pipeline objects if you use the
button.
Annotations is a property on the color map object. You simply get access to the
color map of interest and then change the Annotations property.
>>> colorMap=GetColorTransferFunction('Temp')# Annotations are specified as a flattened list of tuples# (data-value, annotation-text)>>> colorMap.Annotations=['1','Slow', '10', 'Fast']
A picture is worth a thousand words, they say, so let’s just let the picture do
the talking. Categorical color maps allow you to render visualizations as shown
in Fig. 3.26.
Visualization using a categorical color map for discrete coloring
When one thinks of scalar coloring, one is typically talking of mapping
numerical values to colors. However, in some cases, the numerical values are not
really numbers, but enumerations such as elements types and gear types (as in
Fig. 3.26) or generally, speaking, categories. The
traditional approach of using an interpolated color map specifying the range of
values with which to color doesn’t really work here. While users could always play
tricks with the number of discrete steps, multiple control points, and annotations,
it is tedious and cumbersome.
Categorical color maps provide an elegant solution for
such cases. Instead of a continuous color transfer function, the user specifies a
set of discrete values and colors to use for those values. For any element where
the data value matches the values in the lookup table exactly, paraview renders
the specified color; otherwise, the NaN color is used.
The color legend or scalar bar also switches to a new mode where it renders
swatches with annotations, rather than a single bar. You can add custom
annotations for each value in the lookup table.
Default ColorMapEditor when InterpretValuesAsCategories is checked.
To tell paraview that the data array is to be treated as categories for coloring,
check the InterpretValuesAsCategories checkbox in the ColorMapEditor panel. As soon as that’s checked, the panel switches to categorical mode:
The MappingData group is hidden, and the Annotations group becomes a
non-advanced group, i.e., the annotations widget is visible even if the panel is
not showing advanced properties, as is shown in
Fig. 3.27.
The annotations widget will still show any annotations that may have been added
earlier, or it may be empty if none were added. You can add annotations for data values
as was the case before using the buttons on the side of the widget. This time, however, each
annotation entry also has a column for color. If color has not been specified, a
question mark icon will show up; otherwise, a color swatch will be shown. You can
double click the color swatch or the question mark icon to specify the color to
use for that entry. Alternatively, you can choose from a preset collection of
categorical color maps by clicking the button.
As before, you can use Tab↹ key to edit and add multiple values. Hence,
you can first add all the values of interest in one pass and then pick a preset
color map to set colors for the values added. If the preset has fewer colors than
the annotated values, then the user may have to manually set the colors for those
extra annotations.
Common Erros
Categorical color maps are designed for data arrays with enumerations, which are
typically integer arrays. However, they can be used for arrays with floating
point numbers as well. With floating point numbers, the value specified
for annotation may not match the value in the dataset exactly, even when the user
expects it to match. In that case, the NaN color will be used.
>>> categoricalColorMap=GetColorTransferFunction('Modes')>>> categoricalColorMap.InterpretValuesAsCategories=1# specify the labels for the categories. This is similar to how# other annotations are specified.>>> categoricalColorMap.Annotations=['0','Alpha','1','Beta']# now, set the colors for each category. These are an ordered list# of flattened tuples (red, green, blue). The first color gets used for# the first annotation, second for second, and so on>>> categoricalColorMap.IndexedColors=[0.0,0.0,0.0, 0.89, 0.10, 0.10]
Comparative visualization in ParaView refers to the ability to create
side-by-side visualizations for comparing with one another. In its most
basic form, you can indeed use ParaView’s ability to show multiple views side by
side to set up simultaneous visualizations. But, that can get cumbersome too
quickly. Let’s take a look at a simple example: Let’s say you want to do a parameter
study where you want to compare isosurfaces generated by a set of isovalues in a
dataset. To set up such a visualization, you’ll need to first create as many
RenderView s as isovalues. Then, create just as many Contour filters,
setting each one up with a right isovalue for the contour to generate and
display the result in one of the views. As the number of isovalues increases,
you can see how this can get tedious. It is highly error prone, as you need to
keep track of which view shows which isovalue. Now, imagine after having set up
the entire visualization that you need to change the Representation type for
all the of the isosurfaces to Wireframe !
ComparativeView s were designed to handle such use-cases. Instead of
creating separate views, you create a single view RenderView(Comparative) . The view itself comprises of a configurable
\(m\times n\)RenderView s. Any data that you show in this view gets shown in
all the internal views simultaneously. Any display property changes, such as
scalar coloring and representation type are also maintained consistently between
these internal views. The interactions in the internal views are linked, so when
you interact with one, all other views update as well. While this is all
nice and well, the real power of ComparativeView s becomes apparent
when you set up a parameter to vary across the views. This parameter can be
any of the properties on the pipeline modules such as filter properties and
opacity, or it could be the data time. Each of these internal views will
now render the result obtained by setting the parameter as per your selection.
Going back to our original example, we will create a single Contour filter
that we show in RenderView(Comparative) with as many internal views as
the isovalue to compare. Next, we will set up a parameter study for varying the
Isosurfaces property on the Contour filter, and, viola! The view will
generate the comparative visualization for us!
In this chapter, we look at how to configure this view and how to set these
parameters to compare. We limit our discussion to RenderView(Comparative) . However, the same principles are applicable to other comparative
views, including BarChartView(Comparative) and LineChartView(Comparative) .
RenderView(Comparative) in paraview showing a
parameter study. In this case, we are comparing the visualization generated
using different isovalues for the Contour filter. The ComparativeViewInspector dockpanel (on the right) is used to configure the parameter study.
To create RenderView(Comparative) in paraview, split or
close the active view and select RenderView(Comparative) from the new
view creation widget. paraview will immediately show four RenderView s
laid out in a \(2\times 2\) grid. While you cannot resize these internal views,
notice that you can still split the view frame and create other views if
needed.
The Properties panel will show properties similar to those available on the
RenderView under the View properties section. If you change any of
these properties, they will affect all these internal views, e.g., setting the
Background color to Gradient will make all the views show a gradient
background.
ComparativeViewInspector in paraview used to configure the active comparative view.
To configure the comparative view itself, you must to use the
ComparativeViewInspector ( Fig. 4.32)
accessible from the View menu. The
ComparativeViewInspector is a dockable panel that is enabled when the
active view is a comparative view.
To change how many internal views are used in the active comparative view and
how they are laid out, use the Layout . The first value is the number of
views in the horizontal direction and the second is the count in the vertical
direction.
Besides doing a parameter study in side-by-side views, you can also show all the
results in a single view. For that, simply check the
Overlayallcomparisons
checkbox. When checked, instead of getting a grid of \(m\times n\)
views, you will only see one view with all visible data displayed \(m\times n\)
times.
To show data in this view is the same as any other view: Make this view active and
use the PipelineBrowser to toggle the eyeball icons to show data produced
by the selected pipeline module(s). Showing any dataset in this view will
result in the data being shown in all the internal views simultaneously. As is true with
View properties, with Display properties, changing
Coloring , Styling , or any other properties will reflect in all
internal views.
Since the cameras among the internal views are automatically linked, if you
interact with one of the views, all views will also update simultaneously when
you release the mouse button.
RenderView(Comparative) with AnnotateTime filter showing
the time for each of the views. In this case, the parameter study is varying
Time across the views.
To understand how to setup a parameter study, let’s go back to our original
example. Our visualization pipeline is simply
Wavelet\(\rightarrow\)Contour (assuming default property values), and we
are showing the result from the Contour filter in the \(2 \times 2\)RenderView(Comparative) with Overlayallcomparisons unchecked.
Now, we want to vary the Isosurfaces property value for the visualization
in each of the internal views. That’s our parameter to study. Since that’s a
property on the Contour filter, we select the Contour filter instance.
Then, its property Isosurfaces is in the parameter selection
combo-boxes. To add the parameter to the study, you must hit the
button.
The parameter Contour1:Isosurfaces will then show up in the Parameter
list above the combo-boxes. You can delete this parameter by using the
button next to the parameter name.
Did you know?
Notice how this mechanism for setting up a parameter study is similar to
how animations are set up. In fact, under the cover, the two mechanisms are not
that different, and they share a lot of implementation code.
Simultaneously, the table widget below the combo-boxes is populated with a
default set of values for the Isosurfaces . This is where you specify the
parameter values for each of the views. The location of the views matches the
location in the table. Hence, \(0-A\) is the top-left view, \(0-B\) is the second
view from the left in the topmost row, and so on. The parameter value at a
specific location in the table is the value used to generate the visualization
in the corresponding view.
To change the parameter (in our case Isosurfaces ) value, you can double
click on the cell in the table and change it one at a time. Also, to make it
easier to fill the cells with a range of values, you can click and drag over
multiple cells. When you release the mouse, a dialog will prompt you to enter
the data value range ( Fig. 4.34).
In case you selected a combination of rows and columns,
the dialog will also let you select in which direction the parameter is varied
using the range specified. You can choose to vary the parameter horizontally
first, vertically first, or only along one of the directions while keeping the
other constant. This is useful when doing a study with multiple parameters.
Dialog used to select a range of parameter values and control how to vary them in paraview.
As soon as you change the parameter values, the view will update to reflect the
change.
You add annotations like color legends, text, and cube-axes
exactly as you would with a regular RenderView . As with other
properties, annotations will show up in all of the internal views.
Did you know?
You can use the AnnotateTime source or filter to show the data time or
the view time in each of the internal views. If Time is one of the
parameters in your study, the text will reflect the time values for each of
the individual views, as expected ( Fig. 4.33)!
A pipeline module in ParaView does one of two things:
it either generates data or processes input data. To generate data, the module
may use a mathematical model e.g. Sources > Sphere or read a file from
disk. Processing data entails transforming input data by applying defined
operations to generate a new output. ParaView provides a large set of readers, data
sources and data filters that cover the needs of many users. For the
cases where the available collection does not satisfy your needs, ParaView
provides a mechanism to add new modules via plugins. Conventional plugins,
however, are intended for hardcore developers. They are written in C++, using
the data processing APIs provided by ParaView and VTK. The complexity of
building and packaging C++ plugins that work on all distributed versions of
ParaView can be daunting and thus a huge barrier for
even advanced ParaView users. Python-based programmable filters, sources and annotations
provide an easy alternative to this. New modules can be written as Python scripts that
are executed by ParaView to generate, process and/or display data, just like
conventional C++ modules. Since the scripts are standard Python scripts, you
have access to Python packages such as NumPy that provide several numeric
operations useful for data transformation.
In this chapter, we will explore how to use Python to add new data processing
modules to ParaView through examples. For additional explanation of the data
processing API, see Section 6.
Common Errors
In this guide so far, we have been looking at examples of Python scripts for
pvpython. These scripts are used to script the actions you would
perform using the paraview UI. The scripts you would
write for ProgrammableSource , ProgrammableFilter, and
ProgrammableAnnotation are entirely different. The data processing API
executes within the data processing pipeline and, thus, has access to the data
being processed. In client-server mode, this means that such scripts are indeed
executed on the server side, potentially in parallel, across several MPI ranks.
Therefore, attempting to import the paraview.simple Python module in the
ProgrammableSource script, for example, is not supported and will
have unexpected consequences.
With programmable modules, you are writing custom code for filters and sources.
You are expected to understand the basics of a VTK (and ParaView) data
processing pipeline, including the various stages of the pipeline execution as
well as the data model. Refer to Section 3.1 for an overview
of the VTK data model. While a detailed discussion of the VTK pipeline execution
model is beyond the scope of this book, the fundamentals covered in this section,
along with the examples in the rest of this chapter, should help you
get started and write useful modules. For a primer on the details of the VTK
pipeline execution stages, see [BerkGeveci].
To create the programmable source, filter, or annotation in paraview,
you use the Sources > Programmable Source, Filters > Programmable Filter
or Sources > Programmable Annotation menus, respectively.
Since the ProgrammableFilter and ProgrammableAnnotation are filters,
like other filters, they get connected to the currently active source(s), i.e., the
currently active source(s) become the input to this new filter. ProgrammableSource , on the other hand, does not have any inputs.
Properties panel for ProgrammableFilter in paraview.
One of the first things that you specify after creating a programmable filter or
source is the OutputDataSetType . This option lets you select the type
of dataset this module will produce. The options provided include several of the
data types discussed in Section 3.1. Additionally, for the
ProgrammableFilter , you can select SameasInput to indicate that
the filter preserves the input dataset type.
Next is the primary part: the Script . This is where you enter the Python
script to generate or process from the inputs the dataset that the module will
produce. As with any Python script, you can import other Python packages and
modules in this script. Just be aware that when running in client-server mode,
this script is going to be executed on the server side. Accordingly, any modules or
packages you import must be available on the server side to avoid errors.
The script gets executed in what’s called the RequestData pass of the
pipeline execution. This is the pipeline pass in which an algorithm is expected
to produce the output dataset.
There are several other passes in a pipeline’s execution. The ones for which you
can specify a Python script to execute in the programmable filter and source are:
RequestInformation: In this pass, the algorithm is expected to
provide the pipeline with any meta-data available about the data that will be
produced by it. This includes things like number of timesteps in the dataset
and their time values for temporal datasets or extents for
structured datasets. This gets called before RequestData pass. In the
RequestData pass, the pipeline could potentially qualify the request
based on the meta-data provided in this pass. For example, if an algorithm announces
that the temporal dataset has multiple timesteps, the pipeline could request that
the algorithm produce data for one of those timesteps in RequestData .
RequestUpdateExtent: In this pass, a filter gets the opportunity
to qualify requests for execution passed on to the upstream pipeline. As an example, if
an upstream reader announced in its RequestInformation script that it can
produce several timesteps, in RequestUpdateExtent, this filter can
make a request to the upstream reader for a specific timestep. This pass
gets called after RequestInformation, but before RequestData .
It’s not very common to provide a script for this pass.
You can specify the script for the RequestInformation pass in
RequestInformationScript and for the RequestUpdateExtent pass in
RequestUpdateExtentScript . Since the RequestUpdateExtent pass does not make
much sense for an algorithm that does not have any inputs, RequestUpdateExtentScript
is not available on ProgrammableSource . ProgrammableAnnotation
only has a RequestData script as this is the only one that make sense in this context.
In this section, we look at several recipes for ProgrammableSource . A
common use of ProgrammableSource is to prototype readers. If your reader
library already provides a Python API, then you can easily import the
appropriate Python package to read your dataset using ProgrammableSource .
Did you know?
Most of the examples in this chapter use a NumPy-centric API for accessing
and creating data arrays. Additionally, you can use VTK’s
Python wrapped API for creating and accessing arrays. However, given the ubiquity
of NumPy, there is rarely any need for using VTK’s API directly.
For this example, we will read in a CSV file to produce a Table
( Section 3.1.9) using ProgrammableSource . We will
use NumPy to do the parsing of the CSV files and pass the arrays read in
directly to the pipeline. Note that the OutputDataSetType must be set
to vtkTable .
# Code for 'Script'# We will use NumPy to read the csv file.# Refer to NumPy documentation for genfromtxt() for details on# customizing the CSV file parsing.importnumpyasnp# assuming data.csv is a CSV file with the 1st row being the names names for# the columnsdata=np.genfromtxt("data.csv",dtype=None,names=True,delimiter=',',autostrip=True)fornameindata.dtype.names:array=data[name]# You can directly pass a NumPy array to the pipeline.# Since ParaView expects all arrays to be named, you# need to assign it a name in the 'append' call.output.RowData.append(array,name)
Building on the example from Section 5.2.1,
let’s say we have a series of files that we
want to read in as a temporal series. Recall from
Section 5.1 that meta-data about data to
be produced, including timestep information, is announced in
RequestInformation pass. Hence, for this example, we will need to specify
the RequestInformationScript as well.
As was true earlier, OutputDataSetType must be set to vtkTable .
Now, to announce the timesteps, we use the following as the
RequestInformationScript .
# Code for 'RequestInformation Script'.defsetOutputTimesteps(algorithm,timesteps):"helper routine to set timestep information"executive=algorithm.GetExecutive()outInfo=executive.GetOutputInformation(0)outInfo.Remove(executive.TIME_STEPS())fortimestepintimesteps:outInfo.Append(executive.TIME_STEPS(),timestep)outInfo.Remove(executive.TIME_RANGE())outInfo.Append(executive.TIME_RANGE(),timesteps[0])outInfo.Append(executive.TIME_RANGE(),timesteps[-1])# As an example, let's say we have 4 files in the file series that we# want to say are producing time 0, 10, 20, and 30.setOutputTimesteps(self,(0,10,20,30))
The Script is similar to earlier, except that we will read a specific
CSV file based on which timestep was requested.
# Code for 'Script'defGetUpdateTimestep(algorithm):"""Returns the requested time value, or None if not present"""executive=algorithm.GetExecutive()outInfo=executive.GetOutputInformation(0)returnoutInfo.Get(executive.UPDATE_TIME_STEP()) \
ifoutInfo.Has(executive.UPDATE_TIME_STEP())elseNone# This is the requested time-step. This may not be exactly equal to the# timesteps published in RequestInformation(). Your code must handle that# correctly.req_time=GetUpdateTimestep(self)# Now, use req_time to determine which CSV file to read and read it as before.# Remember req_time need not match the time values put out in# 'RequestInformation Script'. Your code need to pick an appropriate file to# read, irrespective....# TODO: Generate the data as you want.# Now mark the timestep produced.output.GetInformation().Set(output.DATA_TIME_STEP(),req_time)
This is similar to Section 5.2.1. Now, however, let’s say the CSV has three
columns named X, Y and Z that we want to treat as point coordinates and
produce a vtkPolyData with points instead of a vtkTable . For that, we first
ensure that OutputDataSetType is set to vtkPolyData . Next, we use
the following Script :
# Code for 'Script'fromvtk.numpy_interfaceimportalgorithmsasalgsfromvtk.numpy_interfaceimportdataset_adapterasdsaimportnumpyasnp# assuming data.csv is a CSV file with the 1st row being the names names for# the columnsdata=np.genfromtxt("/tmp/points.csv",dtype=None,names=True,delimiter=',',autostrip=True)# convert the 3 arrays into a single 3 component array for# use as the coordinates for the points.coordinates=algs.make_vector(data["X"],data["Y"],data["Z"])# create a vtkPoints container to store all the# point coordinates.pts=vtk.vtkPoints()# numpyTovtkDataArray is needed to called directly to convert the NumPy# to a vtkDataArray which vtkPoints::SetData() expects.pts.SetData(dsa.numpyTovtkDataArray(coordinates,"Points"))# set the pts on the output.output.SetPoints(pts)# next, we define the cells i.e. the connectivity for this mesh.# here, we are creating merely a point could, so we'll add# that as a single poly vextex cell.numPts=pts.GetNumberOfPoints()# ptIds is the list of point ids in this cell# (which is all the points)ptIds=vtk.vtkIdList()ptIds.SetNumberOfIds(numPts)forainrange(numPts):ptIds.SetId(a,a)# Allocate space for 1 cell.output.Allocate(1)output.InsertNextCell(vtk.VTK_POLY_VERTEX,ptIds)# We can also pass all the array read from the CSV# as point data arrays.fornameindata.dtype.names:array=data[name]output.PointData.append(array,name)
The thing to note is that this time, we need to define the geometry and topology for
the output dataset. Each data type has different requirements on how these are
specified. For example, for unstructured datasets like vtkUnstructuredGrid and
vtkPolyData, we need to explicitly specify the geometry and all the
connectivity information. For vtkImageData, the geometry is defined using
origin, spacing, and extents, and connectivity is implicit.
This recipe shows how to read raw binary data representing a 3D volume. Since
raw binary files don’t encode information about the volume extents and data
type, we will assume that the extents and data type are known and fixed.
For producing image volumes, you need to provide the information about the
structured extents in RequestInformation. Ensure that the OutputDataSetType is set to vtkImageData .
# Code for 'RequestInformation Script'.executive=self.GetExecutive()outInfo=executive.GetOutputInformation(0)# we assume the dimensions are (48, 62, 42).outInfo.Set(executive.WHOLE_EXTENT(),0,47,0,61,0,41)outInfo.Set(vtk.vtkDataObject.SPACING(),1,1,1)
The Script to read the data can be written as follows.
# Code for 'Script'importnumpyasnp# read raw binary data.# ensure 'dtype' is set properly.data=np.fromfile("HeadMRVolume.raw",dtype=np.uint8)dims=[48,62,42]assertdata.shape[0]==dims[0]*dims[1]*dims[2],"dimension mismatch"output.SetExtent(0,dims[0]-1,0,dims[1]-1,0,dims[2]-1)output.PointData.append(data,"scalars")output.PointData.SetActiveScalars("scalars")
ProgrammableSource used to read HeadMRVolume.raw file available in the VTK data repository.
Here is another polydata source example. This time, we generate the data programmatically.
# Code for 'Script'#This script generates a helix curve.#This is intended as the script of a 'Programmable Source'importmathimportnumpyasnpfromvtk.numpy_interfaceimportalgorithmsasalgsfromvtk.numpy_interfaceimportdataset_adapterasdsanumPts=80# Points along Helixlength=8.0# Length of Helixrounds=3.0# Number of times around# Compute the point coordinates for the helix.index=np.arange(0,numPts,dtype=np.int32)scalars=index*rounds*2*math.pi/numPtsx=index*length/numPts;y=np.sin(scalars)z=np.cos(scalars)# Create a (x,y,z) coordinates array and associate that with# points to pass to the output dataset.coordinates=algs.make_vector(x,y,z)pts=vtk.vtkPoints()pts.SetData(dsa.numpyTovtkDataArray(coordinates,'Points'))output.SetPoints(pts)# Add scalars to the output point data.output.PointData.append(index,'Index')output.PointData.append(scalars,'Scalars')# Next, we need to define the topology i.e.# cell information. This helix will be a single# polyline connecting all the points in order.ptIds=vtk.vtkIdList()ptIds.SetNumberOfIds(numPts)foriinrange(numPts):#Add the points to the line. The first value indicates#the order of the point on the line. The second value#is a reference to a point in a vtkPoints object. Depends#on the order that Points were added to vtkPoints object.#Note that this will not be associated with actual points#until it is added to a vtkPolyData object which holds a#vtkPoints object.ptIds.SetId(i,i)# Allocate the number of 'cells' that will be added. We are just# adding one vtkPolyLine 'cell' to the vtkPolyData object.output.Allocate(1,1)# Add the poly line 'cell' to the vtkPolyData object.output.InsertNextCell(vtk.VTK_POLY_LINE,ptIds)
ProgrammableSource output generated using the script in
Section 5.2.5. This visualization uses Tube
filter to make the output polyline more prominent.
One of the differences between the ProgrammableSource and the
ProgrammableFilter is that the latter expects at least 1 input. Of course,
the code in the ProgrammableFilter is free to disregard the input entirely
and work exactly as ProgrammableSource . ProgrammableFilter is
designed to customize data transformations. For example, it is useful when you
want to compute derived quantities using expressions not directly possible with
PythonCalculator and Calculator or when you want to use other Python
packages or even VTK filters not exposed in ParaView for processing the inputs.
In this section, we look at various recipes for ProgrammableFilter s.
Adding a new point/cell data array based on an input array
PythonCalculator provides an easy mechanism of computing derived
variables. You can also use the ProgrammableFilter .
Typically, for such cases, ensure that the OutputDataSetType is set to
SameasInput .
# Code for 'Script'# 'inputs' is set to an array with data objects produced by inputs to# this filter.# Get the first input.input0=inputs[0]# compute a value.dataArray=input0.PointData["V"]/2.0# To access cell data, you can use input0.CellData.# 'output' is a variable set to the output dataset.output.PointData.append(dataArray,"V_half")
The thing to note about this code is that it will work as expected even when
the input dataset is a composite dataset such as a Multiblock dataset
( Section 3.1.10). Refer to Section 6
for details on how this works. There are cases, however, when you may want to
explicitly iterate over blocks in an input multiblock dataset. For that, you can
use the following snippet.
input0=inputs[0]ifinput0.IsA("vtkCompositeDataSet"):# iterate over all non-empty blocks in the input# composite dataset, including multiblock and AMR datasets.forblockininput0:processBlock(block)else:processBlock(input0)
This recipe computes the volume for each tetrahedral cell in the input dataset.
You can always simply use the PythonCalculator to compute cell volume
using the expression volume(inputs[0]). This recipe is provided to
illustrate the API.
Ensure that the output type is set to SameasInput , and this filter assumes
the input is an unstructured grid ( Section 3.1.7).
# Code for 'Script'.importnumpyasnp# This filter computes the volume of the tetrahedra in an unstructured mesh.# Note, this is just an illustration and not the most efficient way for# computing cell volume. You should use 'Python Calculator' instead.input0=inputs[0]numTets=input0.GetNumberOfCells()volumeArray=np.empty(numTets,dtype=np.float64)foriinrange(numTets):cell=input0.GetCell(i)p1=input0.GetPoint(cell.GetPointId(0))p2=input0.GetPoint(cell.GetPointId(1))p3=input0.GetPoint(cell.GetPointId(2))p4=input0.GetPoint(cell.GetPointId(3))volumeArray[i]=vtk.vtkTetra.ComputeVolume(p1,p2,p3,p4)output.CellData.append(volumeArray,"Volume")
In this example, the ProgrammableFilter takes two input datasets: A and B. It
outputs dataset B with a new scalar array that labels the points in B that
are also in A. You should select two datasets in the pipeline browser and then
apply the programmable filter.
# Code for 'Script'# Get the two inputsA=inputs[0]B=inputs[1]# use len(inputs) to determine now many inputs are connected# to this filter.# We use numpy.in1d to test all which point coordinate components# in B are present in A as well.maskX=np.in1d(B.Points[:,0],A.Points[:,0])maskY=np.in1d(B.Points[:,1],A.Points[:,1])maskZ=np.in1d(B.Points[:,2],A.Points[:,2])# Combining each component mask, we get the mask for point# itself.mask=maskX&maskY&maskZ# Now convert it to uint8, since bool arrays# cannot be passed back to the VTK pipeline.mask=np.asarray(mask,dtype=np.uint8)# Initialize the output and add the labels array# This ShallowCopy is needed since by default the output is# initialized to be a shallow copy of the first input (inputs[0]),# but we want it to be a description of the second input.output.ShallowCopy(B.VTKObject)output.PointData.append(mask,"labels")
Note in the script above the two inputs are defined in an inputs array. The
order of elements in this array is determined by the order the data sources were
selected in the PipelineBrowser . Hence, inputs[0] is the first data source
selected and inputs[1] is the second.
The main difference between the programmable annotation
and other programmable modules is that output is intended to be shown
as a text representation. The output is expected to be a vtkTable containing
a single one-component string array containing a single tuple.
This tuple will be shown as a text representation, similar to the output
of the Text source or the PythonAnnotation filter.
By default, the ProgrammableAnnotation script already contains
all that is needed to create this table, it just need to be filled up.
Similar to the ProgrammableFilter, the ProgrammableAnnotation is designed
to customize data display. For example, it is useful when you
want to compute derived quantities using expressions not directly possible with
PythonAnnotation and other annotation filters or when you want to use other
Python packages or even VTK filters not exposed in ParaView for processing the inputs.
In this section, we look at various recipes for ProgrammableAnnotation s.
Displaying the number of cells with a non-zero volume
PythonAnnotation provides easy mechanism to compute many values
on datasets and arrays, but conditional operation like the one proposed
here require the use of a ProgrammableAnnotation .
# Code for 'Script'# 'inputs' is set to an array with data objects produced by inputs to# this filter.# Get the first input.input0=inputs[0]# compute the volume of each cell of the inputvols=volume(input0)# the codepath for composite dataset and non composite dataset can't be shared# with this operationifinput0.IsA("vtkCompositeDataSet"):# create a running sum to iterate over blocksnum=0;# iterate over blocksforiinrange(size(vols.Arrays)):# count the number of cells with a non-zero volume in this block# and add it to the running sumnum+=sum(val>0forvalinvols.Arrays[i])else:# non-composite case : just count the number of cells with a non-zero volumenum=sum(val>0forvalinvols)# standard code to display the resultto=self.GetTableOutput()arr=vtk.vtkStringArray()arr.SetName("Text")arr.SetNumberOfComponents(1)arr.InsertNextValue(str(num))to.AddColumn(arr)
PythonAnnotation does not provides any mechanism to import Python modules
while doing that in a ProgrammableAnnotation is trivial.
# Code for 'Script'# import needed python modulesfromdatetimeimportdateimportplatform# construct the string to displaystring="Date: %s\n"%date.today()string+="System: %s"%platform.platform()# standard code to display the stringto=self.GetTableOutput()arr=vtk.vtkStringArray()arr.SetName("Text")arr.SetNumberOfComponents(1)arr.InsertNextValue(string)to.AddColumn(arr)
ProgrammableSource and ProgrammableFilter are convenient ways to
prototype a Python-based data processing module. If you want to distribute such
modules, or package them into modules with user interfaces,
for example, then VTKPythonAlgorithmBase -based approach is recommended instead.
Here, you write a Python class by subclassing VTKPythonAlgorithmBase and
implementing methods to do the data processing, just like any other VTK-based
filter or source. Using Python syntactic add-ons called decorators to
annotate your class, you can easily expose the class to ParaView as a filter or
a source, and ParaView will automatically add UI widgets to control parameters, etc.
Let’s start with the simple script featured in
Fig. 5.30. Here’s the Python script to
create a VTKPythonAlgorithmBase subclass for the same operation.
fromvtkmodules.vtkCommonDataModelimportvtkDataSetfromvtkmodules.util.vtkAlgorithmimportVTKPythonAlgorithmBasefromvtkmodules.numpy_interfaceimportdataset_adapterasdsaclassHalfVFilter(VTKPythonAlgorithmBase):def__init__(self):VTKPythonAlgorithmBase.__init__(self)defRequestData(self,request,inInfo,outInfo):# get the first input.input0=dsa.WrapDataObject(vtkDataSet.GetData(inInfo[0]))# compute a value.data=input0.PointData["V"]/2.0# add to outputoutput=dsa.WrapDataObject(vtkDataSet.GetData(outInfo))output.ShallowCopy(input0.VTKObject)output.PointData.append(data,"V_half");return1
To expose this filter in ParaView, you have to add decorators to the class
definition as follows:
# same imports as earlier.fromvtkmodules.vtkCommonDataModelimportvtkDataSetfromvtkmodules.util.vtkAlgorithmimportVTKPythonAlgorithmBasefromvtkmodules.numpy_interfaceimportdataset_adapterasdsa# new module for ParaView-specific decorators.fromparaview.util.vtkAlgorithmimportsmproxy,smproperty,smdomain@smproxy.filter(label="Half-V Filter")@smproperty.input(name="Input")classHalfVFilter(VTKPythonAlgorithmBase):# the rest of the code here is unchanged.def__init__(self):VTKPythonAlgorithmBase.__init__(self)defRequestData(self,request,inInfo,outInfo):# get the first input.input0=dsa.WrapDataObject(vtkDataSet.GetData(inInfo[0]))# compute a value.data=input0.PointData["V"]/2.0# add to outputoutput=dsa.WrapDataObject(vtkDataSet.GetData(outInfo))output.ShallowCopy(input0.VTKObject)output.PointData.append(data,"V_half");return1
To use this new filter, save this to a *.py file, and load it as a plugin using
the PluginManager from Tools > Plugin Manager. On success, you will
see a Half-VFilter in the Filters menu.
Besides exposing class as filters, or sources, you can use the decorators to add
UI widgets to call methods on the class to set parameters.
The follow examples adds a new source named Python-basedSuperquadricSourceExample , with UI to control various parameters.
# to add a source, instead of a filter, use the `smproxy.source` decorator.@smproxy.source(label="Python-based Superquadric Source Example")classPythonSuperquadricSource(VTKPythonAlgorithmBase):"""This is dummy VTKPythonAlgorithmBase subclass that simply puts out a Superquadric poly data using a vtkSuperquadricSource internally"""def__init__(self):VTKPythonAlgorithmBase.__init__(self,nInputPorts=0,nOutputPorts=1,outputType='vtkPolyData')fromvtkmodules.vtkFiltersSourcesimportvtkSuperquadricSourceself._realAlgorithm=vtkSuperquadricSource()defRequestData(self,request,inInfo,outInfo):fromvtkmodules.vtkCommonDataModelimportvtkPolyDataself._realAlgorithm.Update()output=vtkPolyData.GetData(outInfo,0)output.ShallowCopy(self._realAlgorithm.GetOutput())return1# for anything too complex or not yet supported, you can explicitly# provide the XML for the method.@smproperty.xml(""" <DoubleVectorProperty name="Center" number_of_elements="3" default_values="0 0 0" command="SetCenter"> <DoubleRangeDomain name="range" /> <Documentation>Set center of the superquadric</Documentation> </DoubleVectorProperty>""")defSetCenter(self,x,y,z):self._realAlgorithm.SetCenter(x,y,z)self.Modified()# In most cases, one can simply use available decorators.@smproperty.doublevector(name="Scale",default_values=[1,1,1])@smdomain.doublerange()defSetScale(self,x,y,z):self._realAlgorithm.SetScale(x,y,z)self.Modified()@smproperty.intvector(name="ThetaResolution",default_values=16)defSetThetaResolution(self,x):self._realAlgorithm.SetThetaResolution(x)self.Modified()@smproperty.intvector(name="PhiResolution",default_values=16)@smdomain.intrange(min=0,max=1000)defSetPhiResolution(self,x):self._realAlgorithm.SetPhiResolution(x)self.Modified()@smproperty.doublevector(name="Thickness",default_values=0.3333)@smdomain.doublerange(min=1e-24,max=1.0)defSetThickness(self,x):self._realAlgorithm.SetThickness(x)self.Modified()
On loading this script as a plugin and creating the Python-basedSuperquadricSourceExample
source, the Properties panel will be populated
as shown in Fig. 5.33.
Properties panel automatically generated from a decorated Python
class, PythonSuperquadricSource .
The decorators also enable us to add new readers and writers. Here is an
example writer that uses NumPy to write tables as compressed binary arrays.
# `smproxy.writer` decorator register the module as writer for the provided file# extension.@smproxy.writer(extensions="npz",file_description="NumPy Compressed Arrays",support_reload=False)@smproperty.input(name="Input",port_index=0)# this domain lets ParaView know which types of data this writer can write.@smdomain.datatype(dataTypes=["vtkTable"],composite_data_supported=False)classNumpyWriter(VTKPythonAlgorithmBase):def__init__(self):VTKPythonAlgorithmBase.__init__(self,nInputPorts=1,nOutputPorts=0,inputType='vtkTable')self._filename=None@smproperty.stringvector(name="FileName",panel_visibility="never")@smdomain.filelist()defSetFileName(self,fname):"""Specify filename for the file to write."""ifself._filename!=fname:self._filename=fnameself.Modified()defRequestData(self,request,inInfoVec,outInfoVec):fromvtkmodules.vtkCommonDataModelimportvtkTablefromvtkmodules.numpy_interfaceimportdataset_adapterasdsatable=dsa.WrapDataObject(vtkTable.GetData(inInfoVec[0],0))kwargs={}foranameintable.RowData.keys():kwargs[aname]=table.RowData[aname]importnumpynumpy.savez_compressed(self._filename,**kwargs)return1defWrite(self):self.Modified()self.Update()
In Section 5, we looked at several recipes for
writing Python script for data processing that relied heavily on using NumPy for
accessing arrays and performing operations on them. In this chapter,
we take a closer look at the VTK-NumPy integration layer that makes it possible
to use VTK and NumPy together, despite significant differences in the data
representations between the two systems.
Let’s start with a teaser by creating a simple pipeline with Sphere
connected to an Elevation filter, followed by the ProgrammableFilter .
Let’s see how we would access the input data object in the Script for the
ProgrammableFilter .
The importance lies in the last three lines. In particular, note how we used a different API to
access the PointData and the Elevation array in the last two lines. Also note
that, when we printed the Elevation array, the output didn’t look like one from a
vtkDataArray. In fact:
It is all in the numpy_interface module. It ties VTK datasets and data arrays to
NumPy arrays and introduces a number of algorithms that can work on these
objects. There is quite a bit to this module, and we will introduce it piece by
piece in the rest of this chapter.
Please note that this example is not very easily replicated by using pure NumPy.
The gradient function returns the gradient of an unstructured grid – a concept
that does not exist in NumPy. However, the ease-of-use of NumPy is there.
In this section, let’s take a closer look at the dataset_adapter module.
This module was designed to simplify accessing VTK datasets and arrays from
Python and to provide a NumPy-style interface.
Let’s continue with the example from the previous section.
Remember, this script is being put in the ProgrammableFilter ‘s Script ,
connected to the Sphere , followed by the Elevation filter pipeline.
We can access the underlying VTK object using the VTKObject member:
print(type(data.VTKObject))
which produces:
<type'vtkCommonDataModelPython.vtkPolyData'>
What we get as the $inputs$ in the ProgrammableFilter is actually a Python
object that wraps the VTK data object itself. The ProgrammableFilter does
this by manually calling the WrapDataObject function from the
vtk.numpy_interface.dataset_adapter module on the VTK data object.
Note that the WrapDataObject function will return an appropriate wrapper class
for all vtkDataSet subclasses, vtkTable, and all vtkCompositeData subclasses.
Other vtkDataObject subclasses are not currently supported.
VTKObjectWrapper forwards VTK methods to its VTKObject so the VTK API can
be accessed directy as follows:
print(data.GetNumberOfCells())96L
However, VTKObjectWrapper s cannot be directly passed to VTK methods as an argument.
Instead, we must pass the VTK object to the VTK filter, like so:
s.SetInputData(data.VTKObject)
An important thing to note in the example above is how the Python class
vtkShrinkPolyData was imported for use in the script. In VTK, classes are
organized into different groups of related functionality, and these groups can be
invididually imported as Python modules. To use a class, you first identify the module in
which it resides, which can be determined from the Doxygen documentation of the class
[KitwareInc]. Go to the Doxygen page for the class, find the path of the file from
which the documentation was generated at the bottom of the page, which has the form
dox/<firstdirectory>/<seconddirectory>/<classname>. The module is then derived as
vtk<firstdirectory><seconddirectory>. As an example, the documentation for
vtkShrinkPolyData is generated from dox/Filters/General/vtkShrinkPolyData,
hence its module is vtkFiltersGeneral. Then, you can import the class with a
statement of the form.
So far, we have a wrapper for VTK data objects that
partially behaves like a VTK data object. This gets a little bit more
interesting when we start looking at how to access the fields (arrays)
contained within this dataset.
For simplicity, we will embed the output generated by the script in the code
itself and use the >>> prefix to differentiate the code from the
output.
It is possible to access PointData , CellData , FieldData ,
Points (subclasses of vtkPointSet only), and Polygons
(vtkPolyData only) this way. We will continue to add accessors to more
types of arrays through this API.
For this section, let’s change our test pipeline to consist of the Wavelet
source connected to the ProgrammableFilter .
In the Script , we access the RTData point data array as follows:
# Code for 'Script'fromparaview.vtk.vtkFiltersGeneralimportvtkDataSetTriangleFilterimage=inputs[0]rtdata=image.PointData['RTData']# Let's transform this data as well, using another VTK filter.tets=vtkDataSetTriangleFilter()tets.SetInputDataObject(image.VTKObject)tets.Update()# Here, now we need to explicitly wrap the output dataset to get a# VTKObjectWrapper instance.ugrid=dsa.WrapDataObject(tets.GetOutput())rtdata2=ugrid.PointData['RTData']
Here, we created two datasets: an image data (vtkImageData) and an unstructured
grid (vtkUnstructuredGrid). They essentially represent the same data but the
unstructured grid is created by tetrahedralizing the image data. So, we expect
the unstructured grid to have the same points but more cells (tetrahedra).
numpy_interface array objects behave very similar to NumPy arrays. In
fact, arrays from vtkDataSet subclasses are instances of VTKArray, which is a
subclass of numpy.ndarray . Arrays from vtkCompositeDataSet and subclasses are
not NumPy arrays, but they behave very similarly. We will outline the differences in a
separate section. Let’s start with the basics. All of the following work as
expected.
As before, for simplicity, we will embed the output generated by the script in the code
itself and use the >>> prefix to differentiate the code from the
output.
>>> print(rtdata[0])60.763466>>> print(rtdata[-1])57.113735>>> print(repr(rtdata[0:10:3]))VTKArray([ 60.76346588, 95.53707886, 94.97672272, 108.49817657], dtype=float32)>>> print(repr(rtdata+1))VTKArray([ 61.76346588, 86.87795258, 73.80931091, ..., 68.51051331, 44.34006882, 58.1137352 ], dtype=float32)>>> print(repr(rtdata<70))VTKArray([ True , False, False, ..., True, True, True])# We will cover algorithms later. This is to generate a vector field.>>> avector=algs.gradient(rtdata)# To demonstrate that avector is really a vector>>> print(algs.shape(rtdata))(9261,)>>> print(algs.shape(avector))(9261, 3)>>> print(repr(avector[:,0]))VTKArray([ 25.69367027, 6.59600449, 5.38400745, ..., -6.58120966, -5.77147198, 13.19447994])
A few things to note in this example:
Single component arrays always have the following shape: (n-tuples,) and
not (n-tuples, 1)
Multiple component arrays have the following shape: (n-tuples, n-components)
Tensor arrays have the following shape: (n-tuples, 3, 3)
The above holds even for images and other structured data. All arrays
have one dimension (1 component arrays), two dimensions (multi-component arrays), or
three dimensions (tensor arrays).
One more cool thing: It is possible to use boolean arrays to index arrays. Thus,
the following works very nicely:
You can do a lot simply using the array API. However, things get much more
interesting when we start using the numpy_interface.algorithms module. We
introduced it briefly in the previous examples. We will expand on it a bit more
here. For a full list of algorithms, use help(algs) . Here are some
self-explanatory examples:
If you haven’t used the axis argument before, it is pretty easy. When you don’t
pass an axis value, the function is applied to all values of an array without
any consideration for dimensionality. When axis=0 , the function will be applied
to each component of the array independently. When axis=1 , the function will be
applied to each tuple independently. Experiment if this is not clear to you.
Functions that work this way include sum , min , max , std , and var .
Another interesting and useful function is where the indices of an
array are returned where a particular condition occurs.
>>> print(repr(algs.where(rtdata<40)))(array([ 420, 9240]),)# For vectors, this will also return the component index if an axis is not# defined.>>> print(repr(algs.where(avector<-29.7)))(VTKArray([4357, 4797, 4798, 4799, 5239]), VTKArray([1, 1, 1, 1, 1]))
So far, all of the functions that we discussed are directly provided by NumPy.
Many of the NumPy ufuncs are included in the algorithms module. They all work
with single arrays and composite data arrays.
Algorithms also provide some functions that behave somewhat differently than
their NumPy counterparts. These include cross, dot, inverse, determinant,
eigenvalue, eigenvector, etc. See a non-exhaustive list in Section 5.9.3.
All of these functions are applied to each tuple rather than to a whole array/matrix.
For example:
Note that everything above only leveraged per-tuple information and did not rely
on the mesh. One of VTK’s biggest strengths is that its data model supports a
large variety of meshes, while its algorithms work generically on all of these mesh
types. The algorithms module exposes some of this functionality. Other functions
can be easily implemented by leveraging existing VTK filters. We used gradient
before to generate a vector and a matrix. Here it is again:
Functions like this require access to the dataset containing the array and the
associated mesh. This is one of the reasons why we use a subclass of ndarray in
dataset_adapter:
>>> print(repr(rtdata.DataSet))<paraview.vtk.numpy_interface.dataset_adapter.DataSet at 0x11b61e9d0>
Each array points to the dataset containing it. Functions such as gradient use
the mesh and the array together. NumPy provides a gradient function too, you say.
What is so exciting about yours? Well, this:
Gradient and algorithms that require access to a mesh work whether that mesh is
a uniform grid, a curvilinear grid, or an unstructured grid thanks to VTK’s
data model. Take a look at various functions in the algorithms module to see all
the cool things that can be accomplished using it. In the remaining sections, we
demonstrate how specific problems can be solved using these modules.
In this section, we take a closer look at composite datasets. For this example,
our pipeline is Sphere source, and Cone source is set as two
inputs to the ProgrammableFilter .
We can create a multiblock dataset in the ProgrammableFilter ‘s Script
as follows:
# Let's assume inputs[0] is the output from Sphere and# inputs[1] is the output from Cone.mb=vtk.vtkMultiBlockDataSet()mb.SetBlock(0,inputs[0].VTKObject)mb.SetBlock(1,inputs[1].VTKObject)
Many of VTK’s algorithms work with composite datasets without any change. For example:
Now that we have a composite dataset with a scalar, we can use numpy_interface .
As before, for simplicity, we will embed the output generated by the script in the code
itself and use the >>> prefix to differentiate the code from the
output.
>>> fromparaview.vtk.numpy_interfaceimportdataset_adapterasdsa>>> mbw=dsa.WrapDataObject(mbe)>>> print(repr(mbw.PointData.keys()))['Normals', 'Elevation']>>> elev=mbw.PointData['Elevation']>>> print(repr(elev))<paraview.vtk.numpy_interface.dataset_adapter.VTKCompositeDataArray at 0x1189ee410>
Note that the array type is different than we have previously seen
(VTKArray). However, it still works the same way.
The return value is a composite array consisting of two VTKArrays. The [] operator
simply returned the first four values of each array. In general, all indexing
operations apply to each VTKArray in the composite array collection. It is similar
for algorithms, where:
Notice how the second array is a VTKNoneArray . This is because vtkConeSource
does not produce normals. Where an array does not exist, we use a VTKNoneArray
as placeholder. This allows us to maintain a one-to-one mapping between datasets
of a composite dataset and the arrays in the VTKCompositeDataArray. It also
allows us to keep algorithms working in parallel without a lot of specialized
code.
Where many of the algorithms apply independently to each array in a collection,
some algorithms are global. Take min and max , for example, as we demonstrated above.
It is sometimes useful to get per-block answers. For this, you can use
_per_block algorithms.
Once you grasp these features, you should be able to use composite arrays very
similarly to single arrays.
A final note on composite datasets: The composite data wrapper provided by
numpy_interface.dataset_adapter offers a few convenience functions to traverse
composite datasets. Here is a simple example:
One of the goals of the ParaView application is enabling data analysis and
visualization for large datasets. ParaView was born out of the need for
visualizing simulation results from simulations run on supercomputing
resources that are often too big for a single desktop machine to
handle. To enable interactive visualization of such datasets, ParaView uses
remote and/or parallel data processing. The basic concept is that if a
dataset cannot fit on a desktop machine due to memory or other
limitations, we can split the dataset among a cluster of machines,
driven from your desktop. In this chapter, we will look at the basics
of remote and parallel data processing using ParaView. For information on
setting up clusters, please refer to the ParaView
Wiki [ThePCommunity].
Did you know?
Remote and parallel processing are often used together, but they refer to
different concepts, and it is possible to have one without the other.
In the case of ParaView, remote processing refers to the concept of
having a client, typically paraview or pvpython, connecting to a pvserver, which
could be running on a different, remote machine. All the data
processing and, potentially, the rendering can happen on the
pvserver. The client drives the visualization process by
building the visualization pipeline and viewing the generated results.
Parallel processing refers to a concept where instead of single core
— which we call a rank — processing the entire dataset, we
split the dataset among multiple ranks. Typically, an instance of
pvserver runs in parallel on more than one rank. If a
client is connected to a server that runs in parallel, we are using
both remote and parallel processing.
In the case of pvbatch, we have an application that operates in parallel
but without a client connection. This is a case of parallel
processing without remote processing.
Let’s consider a simple use-case. Let’s say you have two computers, one located
at your office and another in your home. The one at the office is a nicer,
beefier machine with larger memory and computing capabilities than the one at
home. That being the case, you often run your simulations on the office
machine, storing the resulting files on the disk attached to your office
machine. When you’re at work, to visualize those results, you simply launch
paraview and open the data file(s). Now, what if you need to
do the visualization and data analysis from home? You have several options:
You can copy the data files over to your home machine and then use
paraview to visualize them. This is tedious, however, as you not only
have to constantly keep copying/updating your files manually, but your machine
has poorer performance due to the decreased compute capabilities and memory
available on it!
You can use a desktop sharing system like Remote Desktop or
VNC, but those can be flaky depending on your network connection.
Alternatively, you can use ParaView’s remote processing capabilities. The
concept is fairly simple. You have two separate processes: pvserver (which runs
on your work machine) and a paraview client (which runs on your home machine).
They communicate with each other over sockets (over an SHH tunnel, if needed).
As far as using paraview in this mode, it’s no different than how we have been
using it so far – you create pipelines and then look at the data produced by
those pipelines in views and so on. The pipelines themselves, however, are created
remotely on the pvserver process. Thus, the pipelines have access to the disks
on your work machine. The OpenFile dialog will in fact browse the file
system on your work machine, i.e., the machine on which pvserver is running. Any
filters that you create in your visualization pipeline execute on the
pvserver.
While all the data processing happens on the pvserver, when it
comes to rendering, paraview can be configured to either do the rendering on
the server process and deliver only images to the client (remote rendering)
or to deliver the geometries to be rendered to the client and let it do the
rendering locally (local rendering).
When remote rendering, you’ll be using the graphics capabilities on your work
machine (the machine running the pvserver). Every time a new rendering needs to
be obtained (for example, when pipeline parameters are changed or you interact
with the camera, etc.), the pvserver process will re-render a new image and
deliver that to the client. When local rendering, the geometries to be rendered
are delivered to the client and the client renders those locally. Thus, not all
interactions require server-side processing. Only when the
visualization pipeline is updated does the server need to deliver
updated geometries to the client.
To begin using ParaView for remote data processing and visualization, we must
first start the server application pvserver on the remote system. To do this,
connect to your remote system using a shell and run:
>pvserver
You will see this startup message on the terminal:
To connect to this server with the
paraview client, select File > Connect or click
the icon in the toolbar to bring up the
ChooseServerConfiguration dialog.
The ChooseServerConfiguration dialog is used to connect to a server.
Common Errors
If your server is behind a firewall and you are attempting to connect
to it from outside the firewall, the connection may not be established
successfully. You may also try reverse connections ( Section 7.4)
as a workaround for firewalls. Please consult your
network manager if you have network connection problems.
Figure Fig. 7.10 shows the ChooseServerConfiguration dialog with a number of entries for remote servers. In
the figure, a number of servers have already been configured, but when
you first open this dialog, this list will be empty. Before you can
connect to a remote server, you will need to add an entry to the list
by clicking on the AddServer button. When you do, you will see
the EditServerConfiguration dialog as in
Figure Fig. 7.11.
The EditServerConfiguration dialog is used to
configure settings for connecting to remote servers.
You will need to set a name for the connection, the server type, the
DNS name of the host on which you just started the server, and the
port. The default ServerType is set to Client / Server, which
means that the server will be listening for an incoming connection
from the client. There are several other options for this setting that
we will discuss later.
When you are done, click the Configure button. Another dialog, as
shown in Fig. 7.12, will appear
where you specify how to start the server. Since we started the server
manually, we will leave the StartupType on the default
Manual setting. You can optionally set the StartupType to
Command and specify an external shell command to launch a server
process.
Configure the server manually. It must be started outside of ParaView.
When you click the Save button, this particular server
configuration will be saved for future use. You can go back and edit
the server configuration by selecting the entry in the list of servers
and clicking the EditServer button in the ChooseServerConfiguration dialog. You can delete it by clicking the Delete
button.
Server configurations can be imported and exported through the
ChooseServerConfiguration dialog. Use the LoadServers
button to load a server configuration file and the SaveServers
button to save a server configuration file. Files can be exchanged
with others to access the same remote servers.
Did you know?
Visualization centers can provide system-wide server configurations on
web servers to allow non-experts to simply select an already
configured ParaView server. These site-wide settings can be
loaded with the FetchServers button. Advanced users may also want
to specify their own servers in more details.
These features are provided thanks to ParaView Server Configuration files
(Section 7.5).
To connect to the server, select the server configuration you just set
up from the configuration list, modify the timeout in the timeout combo
box if needed and click Connect. ParaView will try to connect to
the server until it succeed or timeout is reached. In that case, you can just
retry as needed. Once the connection steps succeed, we are now connected and
ready to build the visualization pipelines.
Common Errors
ParaView does not perform any kind of authentication when clients
attempt to connect to a server. For that reason, we recommend that you
do not run pvserver on a computing resource that is open to the outside
world.
ParaView also does not encrypt data sent between the client and
server. If your data is sensitive, please ensure that proper network
security measures have been taken. The typical approach is to use an
SSH tunnel within your server configuration files using native SSH support
(Section 7.5.16).
pvserver can be configured to accept connections from multiple clients at the same time.
In this case only one, called the master, can interact with the pipeline.
Others clients are only allowed to visualize the data. The CollaborationPanel
shares information between connected clients.
To enable this mode, pvserver must be started with the --multi-clients flag:
pvserver--multi-clients
If your remote server is accessible from many users, you may want to restrict the access.
This can be done with a connect id.
If your client does not have the same connect-id as the server you want to connect to,
you will be prompted for a connect-id.
Then, if you are the master, you can change the connect-id in the CollaborationPanel.
Note that initial value for connect-id can be set by starting the pvserver
(and respectively paraview) with the --connect-id flag, for instance:
pvserver--connect-id=147
The master client can also disable further connections in the CollaborationPanel
so you can work alone, for instance. Once you are ready, you may allow other people to connect
to the pvserver to share a visualization. This is the default feature when pvserver is
started with --multi-clients--disable-further-connections.
Setting up a client/server visualization pipeline
Using paraview when connected to a remote server is not any different than when
it’s being used in the default stand-alone mode. The only difference, as far as
the user interface goes, is that the PipelineBrowser reflects the name of
the server to which you are connected. The address of the server connection next to
the icon changes from builtin
to cs://myhost:11111 .
Since the data processing pipelines are executing on the server side, all file
I/O also happens on the server side. Hence, the OpenFile dialog, when
opening a new data file, will browse the file system local to the pvserver
executable and not the paraview client.
The pvpython executable can be used by itself for visualization of local
data, but it can also act as a client that connects to a remote pvserver.
Before creating a pipeline in pvpython, use the Connect function:
# Connect to remote server "myhost" on the default port, 11111>>>Connect("myhost")# Connect to remote server "myhost" on a# specified port>>>Connect("myhost",11111)
Now, when new sources are created, the data produced by the sources
will reside on the server. In the case of pvpython, all data remains on
the server and images are generated on the server too. Images are
sent to the client for display or for saving to the local filesystem.
It is frequently the case that remote computing resources are located
behind a network firewall, making it difficult to connect a client
outside the firewall to a server behind it. ParaView provides a way to
set up a reverse connection that reverses the usual client
server roles when establishing a connection.
To use a remote connection, two steps must be performed. First,
in paraview, a new connection must be configured with the connection type
set to reverse. To do this, open the ChooseServerConfiguration
dialog through the File > Connect menu item. Add a new
connection, setting the Name to myhost(reverse)'',andselect``Client/Server(reverseconnection) for ServerType . Click
Configure . In the EditServerLaunchConfiguration dialog that
comes up, set the StartupType to Manual . Save the
configuration. Next, select this configuration and click Connect .
A message window will appear showing that the client is awaiting a
connection from the server.
Message window showing that the client is awaiting a connection from a server.
Second, pvserver must be started with the --reverse-connection
(-rc) flag. To tell pvserver the name of the client, set
the --client-host (-ch) command-line argument to the
hostname of the machine on which the paraview client is running. You
can specify a port with the --server-port (-sp)
command-line argument.
When the server starts, it prints a message indicating the success or
failure of connecting to the client. When the connection is
successful, you will see the following text in the shell:
To wait for reverse connections from a pvserver in pvpython, you use
ReverseConnect instead of Connect .
# To wait for connections from a 'pvserver' on the default port 11111>>>ReverseConnect()# Optionally, you can specify the port number as the argument.>>>ReverseConnect(11111)
In the ChooseServerConfiguration dialog, it is possible
to LoadServers and SaveServers using the dedicated buttons.
Server configurations are stored in ParView Server Configuration files (.pvsc).
These files make it possible to extensively customize the server connection process.
During startup, ParaView looks at several locations for server configurations to load by default.
On Unix-based systems and Mac OS X
default_servers.pvsc in the ParaView executable directory (you can do a ls-l/proc/<paraviewPIDhere>/exe to identify the executable directory)
/usr/share/ParaView/servers.pvsc
$HOME/.config/ParaView/servers.pvsc (ParaView will save user defined servers here)
On Windows
default_servers.pvsc in the ParaView executable directory
%COMMON_APPDATA%\ParaView\servers.pvsc
%APPDATA%\ParaView\servers.pvsc (ParaView will save user defined servers here)
In this use-case, we are connecting to a locally started pvserver (localhost) on the 11111 port,
except that the command to start the server will be automatically called just before connecting to the server,
we will wait for timeout seconds before aborting the connection.
Here, CommandStartup element specify that a command will be run before connecting to the server.
The Command element contains the details about this command, which includes
process_wait, the time in seconds that paraview will wait for the process to start,
delay, the time in seconds paraview will wait after running the command to try to connect and finally,
exec, which is the command that will be run and usually contains the path to pvserver but could also
contain a mpi command to start pvserver distributed or to any script or executable on the localhost
filesystem.
In this use-case, we are setting a configuration for a simple server connection (to a pvserver processes) running on a node named “amber1”, at port 20234.
The pvserver process will be started manually by the user.
Here, name specify the name of the server as it will appear in the pipeline browser, resource identifies the type if the connection (cs – implying client-server), host name and port.
If the port number i.e. :20234 part is not specified in the resource, then the default port number (which is 11111) is assumed. Since the user starts pvserver processes manually, we use ManualStartup.
Case Three: Server connection with user-specified port
This is the same as case two except that we want to ask the user each time the port number to connect to the pvserver at.
Here the only difference is the Options element.
This element is used to specify run-time options that the user specifies when connecting to the server, see this section for a list of available run-time options.
In this case, we want to show the user an integral spin-box to select the port number, hence we use the Range element to specify the type of the option.
When the user connects to this server, he is shown a dialog similarly to the following image:
Case Four: Simple connection to a data-server/render-server
This is the same as case two, except that instead of a single server (i.e. pvserver),
we are connecting to a separate render-server/data-server with pvdataserver running on port 20230 on amber1 and pvrenderserver running port 20233 on node amber2.
The only difference with case two, is the resource specification. cdsrs indicates that it is a client-dataserver-renderserver configuration.
The first host:port pair is the dataserver while the second one is the render server.
Case Five: Connection to a data-server/render-server with user specified server port
This is a combination of case three and case four, where we want to ask the user for the port number for both the render server and the data server.
<Servername="case05"resource="cdsrs://localhost//localhost"><ManualStartup><Options><Optionname="PV_DATA_SERVER_PORT"label="Data Server Port: "><Rangetype="int"min="1"max="65535"step="1"default="11111"/></Option><Optionname="PV_RENDER_SERVER_PORT"label="Render Server Port: "><Rangetype="int"min="1"max="65535"step="1"default="22222"/></Option></Options></ManualStartup></Server>
The XML is quite self-explanatory given what we has already been explained above.
The options dialog produced by this XML looks as follows:
By default the client connects to the server processes. However it is possible to tell the paraview client to wait for the server to connect to it instead.
This is called a reverse connection. In such a case the server processes must be started with --reverse-connection or --rc flag.
To indicate reverse connection in the server configuration xml, the only change is suffixing the resource protocol part with rc (for reverse connection). eg.
As we have seen in case one, the server can be started by ParaView on connection, but this can be combined with the Option element
as seen in case three to create a dynamically generated server command.
<Servername="case07"resource="cs://localhost"><CommandStartup><Options><!-- The user chooses the port on which to start the server --><Optionname="PV_SERVER_PORT"label="Server Port: "><Rangetype="int"min="1"max="65535"step="1"default="11111"/></Option></Options><Commanddelay="5"exec="/path/to/pvserver"><Arguments><Argumentvalue="--server-port=$PV_SERVER_PORT$"/></Arguments></Command></CommandStartup></Server>
As with case one, we are using CommandStartup and Command elements.
Command line arguments can be passed to the command executed using the Arguments element.
All runtime environment variables specified as $name$ are replaced with the actual values.
Eg. in this case $PV_SERVER_PORT$ gets replaced by the port number chosen by the user in the options dialog.
In many cases, a server cluster may be running multiple pvserver (or pvdataserver/pvrenderserver) processes for different users.
In that case we need some level of authentication between the server and the client.
This can be achieved (at a very basic level) with the connect-id option.
If specified on the command line when starting the server processes (using --connect-id) then the server will allow only that client which reports the same connection id to connect.
We also want to avoid port collision with other users, so we use a random port for the server connection.
Here is an example similarly to case seven but with a connect-id option and random server port.
In this case, the readonly attribute on the Option indicates that the value cannot be changed by the user, it is only shown for information purposes.
The default value for the PV_CONNECT_ID and PV_SERVER_PORT is set to random so that ParaView makes up a value at run time.
Of course, in a production environnement they should be assigned by user instead of randomly generated.
In this use case the server process is spawned on some remote host using specifically crafted ssh command. We want the user to be able to specify the ssh executable.
We also want to preserve the ssh executable path across ParaView sessions so that the user does not have to enter it each time.
<Servername="case09"resource="cs://localhost:11111"><CommandStartup><Options><Optionname="SSH_USER"label="SSH Username"save="true"><!-- choose the username. Since 'save' is true, this value will be maintained across sessions --><Stringdefault="user"/></Option><Optionname="SSH_EXE"label="SSH Executable"save="true"><!-- select the SSH executable. Since 'save' is true, this value will also be maintinaed across sessions --><Filedefault="ssh"/></Option></Options><Commandexec="$SSH_EXE$"delay="5"><Arguments><Argumentvalue="-L8080:amber5:11111"/><!-- port forwarding --><Argumentvalue="amber5"/><Argumentvalue="-l"/><Argumentvalue="$SSH_USER$"/><Argumentvalue="/path/to/pvserver"/></Arguments></Command></CommandStartup></Server>
Note here that the value for the exec attribute is set to $SSH_EXE$ hence it gets replaced by the user selected ssh executable.
We use the optional attribute save on the Option element to tell ParaView to preserve the user chosen value across ParaView sessions
so that the user doesn’t have to enter the username and the ssh executable every time he wants to connect to this server.
Did you know?
While SSH connection can be started by crafting the command, ParaView
now support SSH connection natively by specyfing a SSHCommand, see below
for more information.
Case Ten: Starting server using custom script with custom user-settable options
This example will illustrate the full capability of server configuration.
Suppose we have a custom script “MyServerStarter” that takes in multiple arguments to start the server process.
We want the user to be able to set up values for these arguments when he tries to connect to using this configuration.
As an example, let’s say MyServerStarter takes the following arguments:
--force-offscreen-rendering – to indicate use of offscreen rendering
--force-onscreen-rendering – to indicate on-screen rendering (this can be assumed from absence of --force-offscreen-rendering, but we are using it as an example)
--session-name=<string> – some string identifying the session
--mpitype=<mpich1.2|mpich2|openmpi> – choose between available MPI implementations
--num-procs=<num> – number of server processess
--server-port – port number passed the pvserver processes
All (except the –server-port) of these must be settable by the user at the connection time. This can be achieved as follows:
<Servername="case10"resource="cs://localhost"><CommandStartup><Options><Optionname="OFFSCREEN"label="Use offscreen rendering"><Booleantrue="--use-offscreen"false="--use-onscreen"default="false"/></Option><Optionname="SESSIONID"label="Session Identifier"><Stringdefault="session01"/></Option><Optionname="MPITYPE"label="MPI Implementation"><Enumerationdefault="mpich1.2"><Entryvalue="mpich1.2"label="MPICH Ver. 1.2"/><Entryvalue="mpich2"label="MPICH Ver 2.0"/><Entryvalue="openmpi"label="Open MPI"/></Enumeration></Option><Optionname="NUMPROC"label="Number Of Processes"><Rangetype="int"min="1"max="256"step="4"default="1"/></Option></Options><Commandexec="/path/to/MyServerStarter"delay="5"><Arguments><Argumentvalue="--server-port=$PV_SERVER_PORT$"/><Argumentvalue="--mpitype=$MPITYPE$"/><Argumentvalue="--num-procs=$NUMPROC$"/><Argumentvalue="$OFFSCREEN$"/><Argumentvalue="--session-name=$SESSIONID$"/></Arguments></Command></CommandStartup></Server>
Each Option defines a new run-time variable that can be accessed as ${name}$ in the Command section.
When the user tries to connect using this configuration, he is shown the following options dialog:
This can be extended to start the server processes using ssh or any batch scheduler etc. as may be the required by the server administrator.
This can also be set up to use reverse connection (by changing the protocol in the resource attribute).
This is same as case ten with one change: We no longer allow the user to choose the number of processes.
Instead, the number of processes is automatically selected based on the value of the distribution combobox.
The Switch statement can only have Case statements as children, while the Case statement can only have Set statements as children.
Set statements are not much different from Option except that the value is fixed and the user is not prompted to set that value.
If Command element let you craft SSH commands, it can be quite complex to do so and the pipeline
browser in ParaView may not show the correct server as it could connect through a ssh tunnel.
Here, similarly to case one, we use native ssh support to start a pvserver process remotely, on amber1,
before connecting to it directly on the default port:
First SSHCommand element is used instead of Command so that ParaView knows to use native ssh support.
Then the SSHConfig element is used to configure the ssh connection. The user attribute is the SSH user to use with SSH.
If a password is needed, it will be asked on the terminal used to run ParaView, which may not be visible in certain cases.
Case Thirteen: SSH run server command with complex config
Here, similarly to case twelve, we use native ssh support to start a pvserver process remotely, on amber1,
before connecting to it directly, but we specify much more specifically the configuration to use.
<Servername="case13"resource="cs://amber1"><CommandStartup><Options><!-- The user chooses the port on which to start the server --><Optionname="PV_SERVER_PORT"label="Server Port: "><Rangetype="int"min="1"max="65535"step="1"default="11111"/></Option></Options><SSHCommandexec="/path/to/pvserver"delay="5"><SSHConfiguser="user"><Terminalexec="/usr/bin/xterm"/><SSHexec="/usr/bin/ssh"/></SSHConfig><Arguments><Argumentvalue="--server-port=$PV_SERVER_PORT$"/></Arguments></SSHCommand></CommandStartup></Server>
Inside the SSHConfig element, we use different elements.
Here, Terminal element is used to specify that ParaView will try to open a terminal to ask the
user for his password. Here, the terminal executable is specified using the exec attribute.
If it was not, ParaView would try to find one automatically (Linux and Windows).
When troubleshooting server configuration, not using Terminal element is suggested
as the terminal will close as soon as the command finish executing.
On Linux, it is also possible to replace the Terminal element by the AskPass element
to specify the ParaView should use SSH_ASKPASS so that a ask-pass binary is used when asking
for the SSH password.
Finally, the SSH element specify the SSH binary to use thanks to its exec attribute.
We also use PV_SERVER_PORT, similarly to case seven to let user select the port to connect to.
Case Fourteen: SSH run server command with user chosen config
Here, similarly to case thirteen and five, we use native ssh support to start a pvserver process remotely, on amber1,
before connecting to it directly, but we let the user choose interactively some SSH options.
Similarly to all other options, SSH related options can be set interactively by the user.
Here we let the user set the SSH user, the SSH executable as well as the Terminal executable
to use when connecting through ssh.
Case Fifteen: Ssh run server command with reverse connection
Similarly to case twelve and thirteen, we use native ssh support to start a
reverse connection pvserver process remotely, on amber1, before letting it
connect to ParaView using the hostname of the client on static non-default port.
The only difference with case twelve is in the ressource, which now contain the reverse connection
as well as the usage of $PV_CLIENT_HOST$ in the arguments for the reverse connection,
automatically set to the hostname of the client which the server should be able to resolve to an ip
to connect to.
Case Sixteen: Secured Connection to a Server trough SSH tunnel
To communicate securely trough a ssh tunnel, something usually done with a crafted command looking like this:
ssh-L8080:localhost:portuser@remote/path/to/pvserver--sp=port
You would then connect on a server on localhost:8080 within ParaView.
This is complex to set up either manually of with a Command element. Also,
the true server and port will not appear in the pipeline browser in ParaView.
This is however natively supported with SSHCommand element.
Here we create a secured SSH tunnel to amber1 before connecting through the SSH tunnel on
the 11111 port.
Similarly to case thirteen, we only add a PortForwarding element in the SSHConfig element with a local attribute port,
so that ParaView creates a SSH tunnel to connect through.
The $PV_SERVER_PORT$ is automatically set to the value of the port to use within the SSH tunnel.
In ParaView, the tunnel will be integrated nicely in the UI with the correct port and hostname in the pipeline browser,
the server icon will look different with a small lock to note the secured nature of this connection:
Case Seventeen: Secured Reverse Connection from a Server trough SSH tunnel
Similarly to case sixteen, a reverse connection through a SSH tunnel would require to craft a command like this one:
ssh-R8080:localhost:portuser@remote/path/to/pvserver--rc--ch=localhost--sp=8080
You would then connect on a reverse connection server on localhost:8080 on ParaView.
This is complex to set up either manually or with a Command element. Also,
the true server and port will not appear in the pipeline browser in ParaView.
This is however natively supported with SSHCommand.
Here we create a reverse secured SSH tunnel to amber1 before reverse connecting
through the SSH tunnel on a specific port.
We also specify a PortForwarding element in the SSHConfig with a local port to trigger the creation of the SSH tunnel.
Finally, $PV_SSH_PF_SERVER_PORT$ variable should be use by the server to connect through the SSH tunnel to the client.
Did you know?
While SSH native support can simplify the configuration file,
some cases are still not covered and require complex custom command.
Client/DataServer/RenderServer SSH setup are not supported natively,
nested SSH tunnels are not supported natively either.
To create such setup, use of complex Command is needed.
The <Servers> tag is the root element of the document, which contains zero-to-many <Server> tags.
Each <Server> tag represents a configured server:
The name attribute uniquely identifies the server configuration, and is displayed in the user interface.
The timeout attribute specifies the maximum amount of time (in seconds) that the client will wait for the server to start, -1 means forever, default to 60.
The resource attribute specifies the type of server connection, server host(s) and optional port(s) for making a connection. Values are
cs://<host>:<port> - for client-pvserver configurations with forward connection i.e. client connects to the server. If not specified, port default to 11111.
csrc://<host>:<port> - for client-pvserver configurations with reverse connection i.e. server connects to the client. If not specified, port default to 11111.
cdsrs://<ds-host>:<ds-port>//<rs-host>:<rs-port> - for client-pvdataserver-pvrenderserver configurations with forward connection. If not specified, ds-port default to 11111, rs-port default to 22222.
cdsrsrc://<ds-host>:<ds-port>//<rs-host>:<rs-port> - for client-pvdataserver-pvrenderserver configurations with reverse connection. If not specified, ds-port default to 11111, rs-port default to 22222.
The <CommandStartup> tag is used to run an external command to start a server.
An optional <Options> tag can be used to prompt the user for options required at startup.
Each <Option> tag represents an option that the user will be prompted to modify before startup.
The name attribute defines the name of the option, which will become its variable name when used as a run-time environment variable, and for purposes of string-substitution in <Argument> tags.
The label attribute defines a human-readable label for the option, which will be used in the user interface.
The optional readonly attribute can be used to designate options which are user-visible, but cannot be modified.
The optional save attribute can be used to indicate that the value choosen by the user for this option will be saved in the ParaView settins so that it’s preserved across ParaView sessions.
A <Range> tag designates a numeric option that is only valid over a range of values.
The type attribute controls the type of number controlled. Valid values are int for integers and double for floating-point numbers, respectively.
The min and max attributes specify the minimum and maximum allowable values for the option (inclusive).
The step attribute specifies the preferred amount to increment / decrement values in the user interface.
The default attribute specifies the initial value of the option.
As a special-case for integer ranges, a default value of random will generate a random number as the default each time the user is prompted for a value. This is particularly useful with PV_CONNECT_ID and PV_SERVER_PORT.
A <String> tag designates an option that accepts freeform text as its value.
The default attribute specifies the initial value of the option.
A <File> tag designates an option that accepts freeform text along with a file browse button to assist in choosing a filepath
The default attribute specifies the initial value of the option.
A <Boolean> tag designates an option that is either on/off or true/false.
The true attribute specifies what the option value will be if enabled by the user.
The false attribute specifies what the option value will be if disabled by the user.
The default attribute specifies the initial value of the option, either true or false.
An <Enumeration> tag designates an option that can be one of a finite set of values.
The default attribute specifies the initial value of the option, which must be one of its enumerated values.
Each <Entry> tag describes one allowed value.
The name tag specifies the value for that choice.
The label tag provides human-readable text that will be displayed in the user interface for that choice.
A <Command> tag is used to specify the external command and its startup arguments.
The exec attribute specifies the filename of the command to be run. The system PATH will be used to search for the command, unless an absolute path is specified. If the value for this attribute is specified as $STRING$, then it will be replaced with the value of a predefined or user-defined (through <Option/>) variable.
The process_wait attribute specifies a waiting time (in seconds) that ParaView will wait for the exec command to start. Default to 0.
The delay attribute specifies a delay (in seconds) between the time the startup command completes and the time that the client attempts a connection to the server. Default to 0.
<Argument> tags are command-line arguments that will be passed to the startup command.
String substitution is performed on each argument, replacing each $STRING$ with the value of a predefined or user-defined variable.
Arguments whose value is an empty string are not passed to the startup command.
A <SSHCommand> tag is used to specify the external command to be started through ssh
All <Command> related attributes and tags still applies.
A <SSHConfig> tag is used to set the SSH configuration.
The user attribute is used to set the SSH username
A <Terminal> tag is used to inform ParaView to use a terminal to issue ssh commands and ask user for password when needed.
The exec attribute specifies the terminal executable to use, if not set, ParaView will try to find one automatically, on Windows and Linux only.
A <AskPass> tag, which should not be used with <Terminal> tag, can be used to inform ParaView to use a AskPass, using the SSH_ASKPASS environnement variable, on Linux only.
A <SSH> tag, used to specify
the exec attribute that specifies the SSH executable to use.
A <PortForwarding> tag, that indicates to ParaView that a SSH tunnel will need to be created, either forward or reverse depending on the connection type.
the local attribute that specified the local port to use the SSH tunel.
The <ManualStartup> tag indicates that the user will manually start the given server prior to connecting.
An optional <Options> tag can be used to prompt the user for options required at startup. Note that PV_SERVER_PORT, PV_DATA_SERVER_PORT, PV_RENDER_SERVER_PORT, and PV_CONNECT_ID are the only variables that make sense in this context.
When a startup command is run, its environment will include all of the user-defined variables specified in <Option> tags, plus the following predefined variables:
These options can be used in the <Command> or <SSHCommand> elements part of the PVSC files,
as well as extracted from the environnement when running the command.
If an <Option> element defines a variable with the same name as a predefined variable, the <Option> element value takes precedence.
This can be used to override defaults that are normally hidden from the user.
As an example, if a site wants users to be able to override default port numbers, the server configuration might specify an <Option> of PV_SERVER_PORT.
Parallel processing, put simply, implies processing the data in parallel,
simultaneously using multiple workers. Typically, these workers are different
processes that could be running on a multicore machine or on several nodes of a
cluster. Let’s call these ranks. In most data processing and visualization
algorithms, work is directly related to the amount of data that needs to be
processed, i.e., the number of cells or points in the dataset. Thus, a straight-forward
way of distributing the work among ranks is to split an input dataset
into multiple chunks and then have each rank operate only an independent set of
chunks. Conveniently, for most algorithms, the result obtained by splitting the
dataset and processing it separately is same as the result that we’d get if we
processed the dataset in a single chunk. There are, of course, exceptions. Let’s
try to understand this better with an example. For demonstration purposes,
consider this very simplified mesh.
Now, let us say we want to perform visualizations on this mesh using three
processes. We can divide the cells of the mesh as shown below with the
blue, yellow, and pink regions.
Once partitioned, some visualization algorithms will work by simply
allowing each process to independently run the algorithm on its local
collection of cells. Take clipping as an example. Let’s say that we
define a clipping plane and give that same plane to each of the processes.
Each process can independently clip its cells with this plane. The end
result is the same as if we had done the clipping serially. If we were to
bring the cells together (which we would never actually do for large data
for obvious reasons), we would see that the clipping operation took place
correctly.
Unfortunately, blindly running visualization algorithms on partitions of
cells does not always result in the correct answer. As a simple example,
consider the external faces algorithm. The external faces
algorithm finds all cell faces that belong to only one cell, thereby,
identifying the boundaries of the mesh.
Oops! We see that when all the processes ran the external faces algorithm
independently, many internal faces where incorrectly identified as being
external. This happens where a cell in one partition has a neighbor in
another partition. A process has no access to cells in other partitions,
so there is no way of knowing that these neighboring cells exist.
The solution employed by ParaView and other parallel visualization systems
is to use ghost cells . Ghost cells are cells that are held in
one process but actually belong to another. To use ghost cells, we first
have to identify all the neighboring cells in each partition. We then copy
these neighboring cells to the partition and mark them as ghost cells, as
indicated with the gray colored cells in the following example.
When we run the external faces algorithm with the ghost cells, we see that
we are still incorrectly identifying some internal faces as external.
However, all of these misclassified faces are on ghost cells, and the faces
inherit the ghost status of the cell from which it came. ParaView then strips
off the ghost faces, and we are left with the correct answer.
In this example, we have shown one layer of ghost cells: only those cells
that are direct neighbors of the partition’s cells. ParaView also has the
ability to retrieve multiple layers of ghost cells, where each layer
contains the neighbors of the previous layer not already contained in a
lower ghost layer or in the original data itself. This is useful when we have
cascading filters that each require their own layer of ghost cells. They
each request an additional layer of ghost cells from upstream, and then
remove a layer from the data before sending it downstream.
Since we are breaking up and distributing our data, it is prudent to
address the ramifications of how we partition the data. The data shown in
the previous example has a spatially coherent partitioning. That
is, all the cells of each partition are located in a compact region of
space. There are other ways to partition data. For example, you could
have a random partitioning.
Random partitioning has some nice features. It is easy to create and is
friendly to load balancing. However, a serious problem exists with respect
to ghost cells.
In this example, we see that a single level of ghost cells nearly
replicates the entire dataset on all processes. We have thus removed any
advantage we had with parallel processing. Because ghost cells are used so
frequently, random partitioning is not used in ParaView.
The previous section described the importance of load balancing and ghost
levels for parallel visualization. This section describes how to achieve
that.
Load balancing and ghost cells are handled automatically by ParaView when
you are reading structured data (image data, rectilinear grid, and
structured grid). The implicit topology makes it easy to break the data
into spatially coherent chunks and identify where neighboring cells are
located.
It is an entirely different matter when you are reading in unstructured
data (poly data and unstructured grid). There is no implicit topology and
no neighborhood information available. ParaView is at the mercy of how the
data was written to disk. Thus, when you read in unstructured data, there
is no guarantee of how well-load balanced your data will be. It is also
unlikely that the data will have ghost cells available, which means that
the output of some filters may be incorrect.
Fortunately, ParaView has a filter that will both balance your unstructured
data and create ghost cells. This filter is called D3, which is short for
distributed data decomposition. Using D3 is easy; simply attach the filter
(located in Filters > Alphabetical > D3) to whatever
data you wish to repartition.
The most common use case for D3 is to attach it directly to your
unstructured grid reader. Regardless of how well-load balanced the incoming
data might be, it is important to be able to retrieve ghost cell so that
subsequent filters will generate the correct data. The example above shows
a cutaway of the extract surface filter on an unstructured grid. On the
left, we see that there are many faces improperly extracted because we are
missing ghost cells. On the right, the problem is fixed by first using the
D3 filter.
If your unstructured grid data is already partitioned satisfactorily but does
not have ghost cells, it is possible to generate them using the GhostCellsGenerator
filter. This filter can be attached to a source just like the D3 filter.
Unlike D3 , it will not repartition the dataset, it will only generate
ghost cells, which is needed for some algorithms to execute correctly.
The GhostCellsGenerator has several options. BuildIfRequired
tells the filter to generate ghost cells only if required by a downstream filter.
Since computing ghost cells is a computationally and communications intensive
process, turning this option on can potentially save a lot of processing time.
The MinimumNumberOfGhostLevels specifies at least how many ghost levels
should be generated if BuildIfRequired is off. Downstream filters may request
more ghost levels than this minimum, in which case the GhostCellsGenerator
will generate the requested number of ghost levels. The UseGlobalIds option
makes use of a GlobalIds array if it is present if on. If off, ghost cells are
determined by coincident points.
Before we see how to use ParaView for parallel data processing, let’s take a
closer look at the ParaView architecture. ParaView is designed as a three-tier
client-server architecture. The three logical units of ParaView are as follows.
Data Server The unit responsible for data
reading, filtering, and writing. All of the pipeline objects seen in the
pipeline browser are contained in the data server. The data server can
be parallel.
Render Server The unit responsible for
rendering. The render server can also be parallel, in which case built-in
parallel rendering is also enabled.
Client The unit responsible for establishing
visualization. The client controls the object creation, execution, and
destruction in the servers, but does not contain any of the data (thus
allowing the servers to scale without bottlenecking on the client). If
there is a GUI, that is also in the client. The client is always a
serial application.
These logical units need not by physically separated. Logical units are
often embedded in the same application, removing the need for any
communication between them. There are three modes in which you can run
ParaView.
The first mode, with which you are already familiar, is
standalone mode. In standalone mode, the client, data server,
and render server are all combined into a single serial application. When
you run the paraview application, you are automatically connected
to a builtin server so that you are ready to use the full
features of ParaView.
The second mode is client-server mode. In client-server mode,
you execute the pvserver program on a parallel machine and
connect to it with the paraview client application (or pvpython). The
pvserver program has both the data server and render server
embedded in it, so both data processing and rendering take place there.
The client and server are connected via a socket, which is assumed to be a
relatively slow mode of communication, so data transfer over this socket is
minimized. We saw this mode of operation in
Section 7.2.
The third mode is client-render server-data server mode. In this
mode, all three logical units are running in separate programs. As before,
the client is connected to the render server via a single socket
connection. The render server and data server are connected by many socket
connections, one for each process in the render server. Data transfer over
the sockets is minimized.
Although the client-render server-data server mode is supported, we almost
never recommend using it. The original intention of this mode is to take
advantage of heterogeneous environments where one might have a large,
powerful computational platform and a second smaller parallel machine with
graphics hardware in it. However, in practice, we find any benefit is
almost always outstripped by the time it takes to move geometry from the
data server to the render server. If the computational platform is much
bigger than the graphics cluster, then use software rendering on the large
computational platform. If the two platforms are about the same size, just
perform all the computation on the graphics cluster. The executables used for
this mode are paraview (or pvpython) (acting as the client), pvdataserver for
the data-server, and pvrenderserver for the render-server.
To leverage parallel processing capabilities in paraview or pvpython, one has
to use remote visualization, i.e., one has to connect to a pvserver. The
processing for connecting to this pvserver is not different from what we
say in Section 7.2
and Section 7.3. The only thing that changes is how the
pvserver is launched.
You can start pvserver to run on more than one processing core
using mpirun
.
mpirun-np4pvserver
This will run pvserver on four processing cores. It will still listen
for an incoming connection from a client on the default port. The big
difference when running pvserver this way is that when data is loaded
from a source, it will be distributed across the four cores if the
data source is parallelaware and supports distributing the data
across the different processing cores.
To see how this data is distributed, run pvserver as the command above and
connect to it with paraview. Next, create another Sphere source
using Source > Sphere. Change the array to color by to
vtkProcessId . You will see an image like Figure Fig. 7.14.
Sphere source colored by vtkProcessId array that encodes
the processing core on which the sphere data resides. Here, the sphere
data is split among the four processing cores invoked by the
command mpirun-np4pvserver.
If a data reader or source is not parallelaware, you can still get
the benefits of spreading the data among processing cores by using the
D3 filter. This filter partitions a dataset into convex regions
and transfers each region to a different processing core. To see an
example of how D3 partitions a dataset, create a Source > Wavelet
while paraview is still connected to the pvserver. Next, select
Filters > Alphabetical > D3 and click Apply . The output of D3
will not initially appear different from the original wavelet source.
If you color by vtkProcessId , however, you will see the four
partitions that have been distributed to the server processing cores.
Wavelet source processed by the D3 filter and colored by vtkProcessId
array. Note how four regions of the image data are split evenly among the four
processing cores when pvserver is run with mpirun-np4pvserver .
In Section 7.9, we said that to use parallel
processing capabilities, one has to use remote visualization, i.e., one must use
ParaView in a client-server mode with the client (paraview or pvpython)
connecting to a server (pvserver) that is being run in parallel using
mpirun
. However, there is one exception: pvbatch. pvpython and
pvbatch are quite similar in that both are similarly to the python
executable that can be used to run Python scripts. The extra thing that these
executables do when compared with the standard python is that they
initialize the environment so that any scripts that you run will be able to
locate the ParaView Python modules and libraries automatically. pvpython is
exactly like the paraview executable without the GUI. You can think of it as
the GUI from paraview is replaced by a Python interpreter in pvpython.
pvbatch, on the other hand, can be thought of a pvserver where, instead of
taking the control command from a remote client (paraview or pvpython), in
pvbatch, the commands are taken from a Python script that is executed in the
pvbatch executable itself. Since pvbatch is akin to the pvserver, unlike
pvpython, it can be run in parallel using mpirun
. In that case,
the root rank (or the first rank or the rank with index $0$) is the one that
acts as the client, interpreting the Python script to execute the commands.
Since pvbatch is designed to act is its own server, you cannot connect to a
remote server in the Python script, i.e., you cannot use simple.Connect .
Furthermore, pvbatch is designed for batch operation, which means that you can only
specify the Python script as a command line argument. Unlike pvpython, you
cannot run this executable to get an interactive shell to enter Python commands.
# process the sample.py script in single process mode.
>pvbatchsample.py
# process the sample.py script in parallel.
>mpirun-np4sample.py
In general, you should use pvpython if you will be using the interpreter
interactively and pvbatch if you are running in parallel.
Section 3.3 describes how to obtain information
about a data object, but not how to access the data object itself. This
section describes several ways to access data from within a Python script. The
client/server nature of ParaView requires a couple steps to access the raw data.
The Python script runs on the client side in either pvpython or paraview, so
one step involves moving the data from the server to the client. This can be
accomplished with the following:
fromparaview.simpleimport*Connect("myhost")# Create a sphere source on myhosts=Sphere()full_sphere=servermanager.Fetch(s)
Here, the full dataset is moved from the server to the client.
The second step is required to deal with the fact that data on the remote server
may be split across distributed processes. By default,
servermanager.Fetch(s) appends all the pieces on the different remote
processes and produces the appended data set on the client. The exact
append operation depends on the type of dataset being retrieved. Composite datasets
are merged by treating the dataset piece on each distributed process as a block
merged into a new multiblock dataset, polygonal datasets are appended into a single
polygonal dataset, rectilinear grids are appended into a single rectilinear grid,
and other datasets are appended into an unstructured grid. Distributed image
datasets cannot currently be fetched to the client. Care must be taken when
fetching an entire dataset to the client because the data that fits on many
distributed processes on a remote system may not fit in client memory.
Another option is to fetch just a single piece of the dataset on one remote
process to the client. To do this, pass the rank number of the remote process from
which you want to retrieve the data to the Fetch function, e.g.,
# Retrieve the piece of the data set on remote process 2s=Sphere()sphere_piece=servermanager.Fetch(s,2)
Lastly, servermanager.Fetch provides a way to apply helper filters to the
dataset that run at two stages. The filter for the first stage is applied to the
data on each remote process, and the filter for the second stage is applied to the
results from the first stage after they are gathered to the root server process.
The results from the second stage of filtering are then transferred from the root
server process to the client.
In the next example, the ExtractSurface filter is applied to a source with
data on each process in the first stage. The results are then assembled with the
AppendGeometry filter and sent to the client.
Rendering is the process of synthesizing the images that you see based on
your data. The ability to effectively interact with your data depends
highly on the speed of the rendering. Thanks to advances in 3D hardware
acceleration, fueled by the computer gaming market, we have the ability to
render 3D quickly even on moderately-priced computers. But, of course, the
speed of rendering is proportional to the amount of data being rendered.
As data gets bigger, the rendering process naturally gets slower.
To ensure that your visualization session remains interactive, ParaView
supports two modes of rendering that are automatically flipped as
necessary. In the first mode, still render , the data is rendered
at the highest level of detail. This rendering mode ensures that all of
the data is represented accurately. In the second mode,
interactive render , speed takes precedence over accuracy. This
rendering mode endeavors to provide a quick rendering rate regardless of
data size.
While you are interacting with a 3D view (for example, rotating, panning, or
zooming with the mouse), ParaView uses an interactive render. This is
because, during the interaction, a high frame rate is necessary to make these
features usable and because each frame is immediately replaced with a new
rendering while the interaction is occurring so that fine details are less
important during this mode. At any time when interaction of the 3D view is
not taking place, ParaView uses a still render so that the full detail of
the data is available as you study it. As you drag your mouse in a 3D view
to move the data, you may see an approximate rendering.
The full detail will be presented as soon as you release the
mouse button.
The interactive render is a compromise between speed and accuracy. As
such, many of the rendering parameters concern when and how lower levels of
detail are used.
Some of the most important rendering options are the LOD parameters.
During interactive rendering, the geometry may be replaced with a lower
level of detail ( LOD ), an approximate geometry with
fewer polygons.
The resolution of the geometric approximation can be controlled. In the
proceeding images, the left image is the full resolution, the middle image
is the default decimation for interactive rendering, and the right image is
ParaView’s maximum decimation setting.
The 3D rendering parameters are located in the settings dialog box, which is
accessed in the menu from the Edit > Settings menu
(ParaView > Preferences on the Mac). The rendering options in the dialog
are in the RenderView tab.
The options pertaining to the geometric decimation for interactive
rendering are located in a section labeled InteractiveRenderingOptions .
Some of these options are considered advanced, so to access
them, you have to either toggle on the advanced options with the
button or search for the option using the edit box at
the top of the dialog. The interactive rendering options include the
following.
LODThreshold : Set the data size at which to use a decimated
geometry in interactive rendering. If the geometry size is under this
threshold, ParaView always renders the full geometry. Increase this value
if you have a decent graphics card that can handle larger data. Try
decreasing this value if your interactive renders are too slow.
LODResolution : Set the factor that controls how large the
decimated geometry should be. This control is set to a value between 0
and 1. 0 produces a very small number of triangles but, possibly, with a
lot of distortion. 1 produces more detailed surfaces but with larger
geometry.
NonInteractiveRenderDelay : Add a delay between an interactive
render and a still render. ParaView usually performs a still render
immediately after an interactive motion is finished (for example,
releasing the mouse button after a rotation). This option can add a delay
that can give you time to start a second interaction before the still
render starts, which is helpful if the still render takes a long time to
complete.
UseOutlineForLODRendering : Use an outline in place of
decimated geometry. The outline is an alternative for when the geometry
decimation takes too long or still produces too much geometry. However, it
is more difficult to interact with just an outline.
ParaView contains many more rendering settings. Here is a summary of some
other settings that can effect the rendering performance regardless of
whether ParaView is run in client-server mode or not. These options are
spread among several categories, and several are considered advanced.
TranslucentRenderingOptions
DepthPeeling : Enable or disable depth peeling. Depth
peeling is a technique ParaView uses to properly render translucent
surfaces. With it, the top surface is rendered and then “peeled away”
so that the next lower surface can be rendered and so on. If you find
that making surfaces transparent really slows things down or renders
completely incorrectly, then your graphics hardware may not be
implementing the depth peeling extensions well; try shutting off depth
peeling.
DepthPeelingforVolumes : Include volumes in depth peeling to
correctly intermix volumes and translucent polygons.
MaximumNumberOfPeels : Set the maximum number of peels to use with depth peeling. Using
more peels allows more depth complexity, but allowing less peels runs
faster. You can try adjusting this parameter if translucent geometry
renders too slow or translucent images do not look correct.
Miscellaneous
OutlineThreshold : When creating very large datasets, default to the outline
representation. Surface representations usually require ParaView to
extract geometry of the surface, which takes time and memory. For data
with sizes above this threshold, use the outline representation, which
has very little overhead, by default instead.
ShowAnnotation : Show or hide annotation providing
rendering performance information. This information is handy when
diagnosing performance problems.
Note that this is not a complete list of ParaView rendering settings. We
have left out settings that do not significantly affect rendering
performance. We have also left out settings that are only valid for
parallel client-server rendering, which are discussed in
Section 7.12.4.
When performing parallel visualization, we are careful to ensure that the
data remains partitioned among all of the processes up to and including
the rendering processes. ParaView uses a parallel rendering library called
IceT . IceT uses a sort-last algorithm for parallel
rendering. This parallel rendering algorithm has each process
independently render its partition of the geometry and then
composites the partial images together to form the final image.
The preceding diagram is an oversimplification. IceT contains multiple
parallel image compositing algorithms such as binary tree ,
binary swap , and radix-k that efficiently divide work
among processes using multiple phases.
The wonderful thing about sort-last parallel rendering is that its
efficiency is completely insensitive to the amount of data being rendered.
This makes it a very scalable algorithm and well suited to large data.
However, the parallel rendering overhead does increase linearly with the
number of pixels in the image. Consequently, some of the rendering
parameters deal with the image size.
IceT also has the ability to drive tiled displays, which are large, high-resolution
displays comprising an array of monitors or projectors. Using a sort-last
algorithm on a tiled display is a bit counterintuitive because the number
of pixels to composite is so large. However, IceT is designed to take
advantage of spatial locality in the data on each process to drastically
reduce the amount of compositing necessary. This spatial locality can be
enforced by applying the Filters > Alphabetical > D3
filter to your data.
Because there is an overhead associated with parallel rendering, ParaView
has the ability to turn off parallel rendering at any time. When parallel
rendering is turned off, the geometry is shipped to the location where
display occurs. Obviously, this should only happen when the data being
rendered is small.
The overhead incurred by the parallel rendering algorithms is proportional
to the size of the images being generated. Also, images generated on a
server must be transfered to the client, a cost that is also proportional
to the image size. To help increase the frame rate during interaction,
ParaView introduces a new LOD parameter that controls the size of the
images.
During interaction while parallel rendering, ParaView can optionally
subsample the image. That is, ParaView will reduce the
resolution of the image in each dimension by a factor during interaction.
Reduced images will be rendered, composited, and transfered. On the
client, the image is inflated to the size of the available space in the
GUI.
The resolution of the reduced images is controlled by the factor with which
the dimensions are divided. In the proceeding images, the left image has
the full resolution. The following images were rendered with the
resolution reduced by a factor of 2, 4, and 8, respectively.
ParaView also has the ability to compress images before transferring them
from server to client. Compression, of course, reduces the amount of data
transferred and, therefore, makes the most of the available bandwidth.
However, the time it takes to compress and decompress the images adds to
the latency.
ParaView contains several different image compression algorithms for
client-server rendering. The first uses LZ4 compression that is designed
for high-speed compression and decompression. The second
option is a custom algorithm called
Squirt , which stands for Sequential Unified Image Run Transfer.
Squirt is a run-length encoding compression that reduces color depth to
increase run lengths. The third algorithm uses the Zlib
compression library, which implements a variation of the Lempel-Ziv
algorithm. Zlib typically provides better compression than Squirt, but
it takes longer to perform and, hence, adds to the latency. paraview Windows
and Linux executables include a compression option that uses NVIDIA’s
NVPipe library for hardware-accelerated compression and decompression if
a Kepler-class or higher NVIDIA GPU is available.
Like the other 3D rendering parameters, the parallel rendering parameters
are located in the Settings dialog.
The parallel rendering options in the dialog are in the
RenderView tab (intermixed with several other rendering options such as those
described in Section 7.12.1). The parallel and
client-server options are divided among several categories, and several are
considered advanced.
Remote/ParallelRenderingOptions
RemoteRenderThreshold : Set the data size at which to
render remotely in parallel or to render locally. If the geometry is
over this threshold (and ParaView is connected to a remote server), the
data is rendered in parallel remotely, and images are sent back to the
client. If the geometry is under this threshold, the geometry is sent
back to the client, and images are rendered locally on the client.
StillRenderImageReductionFactor :
Set the sub-sampling factor for still (non-interactive) rendering.
Some large displays have more resolution than is really necessary, so
this sub-sampling reduces the resolution of all images displayed.
Client/ServerRenderingOptions
ImageReductionFactor : Set the
interactive subsampling factor. The overhead of parallel rendering is
proportional to the size of the images generated. Thus, you can speed
up interactive rendering by specifying an image subsampling rate. When
this box is checked, interactive renders will create smaller images,
which are then magnified when displayed. This parameter is only used
during interactive renders.
ImageCompression
Before images are shipped from server to client, they can optionally
be compressed using one of three available compression algorithms:
LZ4 , Squirt , or Zlib . To make the
compression more effective, either algorithm can reduce the color resolution
of the image before compression. The sliders determine the amount of color
bits saved. Full color resolution is always used during a still
render.
Suggested image compression presets are provided for several common
network types. When attempting to select the best image compression
options, try starting with the presets that best match your connection.
The default rendering parameters are suitable for most users. However,
when dealing with very large data, it can help to tweak the rendering
parameters. While the optimal parameters depend on your data and the hardware
on which ParaView is running, here are several pieces of advice that you
should follow.
If there is a long pause before the first interactive render of a
particular dataset, it might be the creation of the decimated
geometry. Try using an outline instead of decimated geometry for
interaction. You could also try lowering the factor of the decimation to
0 to create smaller geometry.
Avoid shipping large geometry back to the client. The remote
rendering will use the power of the entire server to render and ship images
to the client. If remote rendering is off, geometry is shipped back to
the client. When you have large data, it is always faster to ship images
than to ship data. (Although, if your network has a high latency, this
could become problematic for interactive frame rates.)
Adjust the interactive image sub-sampling for client-server rendering
as needed. If image compositing is slow, if the connection between
client and server has low bandwidth, or if you are rendering very large
images, then a higher subsample rate can greatly improve your interactive
rendering performance.
Make sure ImageCompression is on. It has a tremendous effect
on desktop delivery performance, and the artifacts it introduces, which
are only there during interactive rendering, are minimal. Lower
bandwidth connections can try using Zlib instead of Squirt compression.
Zlib will create smaller images at the cost of longer
compression/decompression times.
If the network connection has a high latency, adjust the parameters
to avoid remote rendering during interaction. In this case, you can try
turning up the remote rendering threshold a bit, and this is a place
where using the outline for interactive rendering is effective.
If the still (non-interactive) render is slow, try turning on the
delay between interactive and still rendering to avoid unnecessary
renders.
The ParaViewMemoryInspector panel provides users with a convenient way to monitor
ParaView’s memory usage during interactive visualization. It also provides developers with a
point-and-click interface for attaching a debugger to local or remote client and
server processes. As explained earlier, both the Information panel and the
StatisticsInspector are prone to over and under estimate the total memory used
for the current pipeline. The MemoryInspector addresses those issues through
direct queries to the operating system. A number of diagnostic statistics are
gathered and reported, including the total memory used by all processes on a
per-host basis, the total cumulative memory use by ParaView on a per-host basis,
and the individual per-rank use by each ParaView process. When
memory consumption reaches a critical level, either cumulatively on the host
or in an individual rank, the corresponding GUI element will turn red, alerting
you that you are in danger of potentially being shut down. This
gives you a chance to save state and restart the job with more
nodes to avoid losing your work. On the flip side, knowing when you’re not
close to using the full capacity of available memory can be useful to conserve
computational resources by running smaller jobs. Of course, the memory foot print
is only one factor in determining the optimal run size.
The main UI elements of the MemoryInspector panel. A: Process Groups,
B: Per-Host statistics, C: Per-Rank statistics, and D: Update controls.
The MemoryInspector panel displays information about the current memory usage
on the client and server hosts. Fig. 8.12
shows the main UI elements labeled A-D.
A number of additional features are provided via specialized context menus
accessible from the Client and Server group, Host, and Rank’s UI elements.
The main UI elements are:
Process Groups
Client : There is always a client group that reports statistics
about the ParaView client.
Server : When running in client-server mode, a server group
reports statistics about the hosts where pvserver processes are running.
Data Server : When running in client-data-render server mode, a
data server group reports statistics about the hosts where pvdataserver
processes are running.
Render Server : When running in client-data-render server mode, a render
server group reports statistics about the hosts where pvrenderserver processes
are running.
Per-Host Statistics : Per-host statics are reported for each host
where a ParaView process is running. Hosts are organized by host name, which is
shown in the first column. Two statics are reported: 1) total memory used by all
processes on the host and 2) ParaView’s cumulative usage on this host. The
absolute value is printed in a bar that shows the percentage of the total
available memory used. On systems where job-wide resource limits are enforced, ParaView
is made aware of the limits via the PV_HOST_MEMORY_LIMIT environment
variable, in which case, ParaView’s cumulative percent used is computed using the
smaller of the host total and the resource limit.
Update Controls : By default, when the panel is visible, memory use
statistics are updated automatically as pipeline objects are created, modified,
or destroyed and after the scene is rendered. Updates may be triggered manually
by using the refresh button. Automatic updates may be disabled by un-checking
the Auto-update check box. Queries to remote systems have proven to be very
fast even for fairly large jobs. Hence, the auto-update feature is enabled by
default.
Host Properties Dialog : The Host context menu provides the
HostProperties dialog, which reports
various system details such as the OS version and
the CPU version, as well as the memory installed and available to the host context and
process context. While the MemoryInspector
panel reports memory use as a percent of the available in the given context,
the HostProperties dialog
reports the total memory installed and available in each context. Comparing the
installed and available memory can be used to determine if you are impacted by
resource limits.
The MemoryInspectorPanel provides a remote (or local) command feature, allowing
you to execute a shell command on a given host. This feature is exposed via a
specialized Rank item context menu. Because we have information such as a rank’s
process id, individual processes may be targeted. For example, this allows you to
quickly attach a debugger to a server process running on a remote cluster. If
the target rank is not on the same host as the client, then the command is
considered remote. Otherwise, it is considered local. Therefore, remote commands are
executed via ssh
, while local commands are not. A list of command templates is
maintained. In addition to a number of pre-defined command templates, you may
add templates or edit existing ones. The default templates allow you to:
Attach gdb to the selected process
Run top on the host of the selected process
Send a signal to the selected process
Prior to execution, the selected template is parsed, and a list of special tokens
are replaced with runtime-determined or user-provide values. User-provided
values can be set and modified in the dialog’s parameter group. The command,
with tokens replaced, is shown for verification in the dialog’s preview pane.
The following tokens are available and may be used in command templates as needed:
$TERM_EXEC$ : The terminal program that will be used to execute
commands. On Unix systems, xterm is typically used. On Windows systems,
cmd.exe
is typically used. If the program is not in the default
path, then the full path must be specified.
$TERM_OPTS$ : Command line arguments for the terminal program.
On Unix, these may be used to set the terminals window title, size, colors, and
so on.
$SSH_EXEC$ : The program to use to execute remote commands. On
Unix, this is typically ssh. On Windows, one option is
plink.exe.
If the program is not in the default path, then the full
path must be specified.
$FE_URL$ : Ssh URL to use when the remote processes are on
compute nodes that are not visible to the outside world. This token is used to
construct command templates where two ssh hops are made to execute
the command.
$PV_HOST$ : The hostname where the selected process is running.
$PV_PID$ : The process-id of the selected process.
Note: On Windows, the debugging tools found in Microsoft’s SDK need to be
installed in addition to Visual Studio (e.g., windbg.exe).
The ssh program plink.exe for Windows doesn’t parse ANSI
escape codes that are used by Unix shell programs. In general, the Windows-
specific templates need some polishing.
The Process Group’s context menu
provides a back trace signal handler option. When enabled, a signal handler is
installed that will catch signals such as SEGV, TERM, INT, and ABORT and that
will print a stack trace before the process exits. Once the signal handler is
enabled, you may trigger a stack trace by explicitly sending a signal. The stack
trace signal handler can be used to collect information about crashes or to
trigger a stack trace during deadlocks when it’s not possible to ssh
into compute nodes. Sites that restrict users’ ssh
access to compute nodes often provide a way to signal running processes from the
login node. Note that this feature is only available on systems that provide
support for POSIX signals, and we currently only have implemented stack trace
for GNU-compatible compilers.
If the system on which ParaView will run has special resource limits enforced,
such as job-wide memory use limits, or non-standard per-process memory limits,
then the system administrators need to provide this information to the running
instances of ParaView via the following environment variables. For example, those
could be set in the batch system launch scripts.
PV_HOST_MEMORY_LIMIT : For reporting host-wide resource limits.
PV_PROC_MEMORY_LIMIT : For reporting per-process memory limits.
that are not enforced via standard Unix resource limits.
A few of the debugging features (such as printing a stack trace) require debug
symbols. These features will work best when ParaView is built with
CMAKE_BUILD_TYPE=Debug or, for release builds,
CMAKE_BUILD_TYPE=RelWithDebugSymbols.
Composite datasets (Section 3) such as multiblock datasets
and AMR are often encountered when visualizing results from several
scientific simulation codes e.g. OpenFOAM, Exodus, etc. Readers for several of
these simulation file formats support selecting which blocks to read.
Additionally, you may want to control display properties such as visibility, opacity,
and color for individual blocks or subtress. You can use the
MultiblockInspector panel for this.
Fig. 9.1 shows the MultiblockInspector showing the
hierarchy from an Exodus dataset. The panel tracks the active source and reflects the
structure for the data produced by the active source. The display properties reflect
their state in the active view.
To show or hide a block you have to click on the checkbox next to the
block name. Toggling the visibility of a non-leaf block, affects the
visibility of the entire subtree.
The first column reflects the color used for the block. The color for a block
can be specified in multiple ways. First, you can choose to not use any block
specific overrides and simply let the default display properties (
Section 4.3) affect the
rendering. This is the default behavior. When that is the case for any block,
it is indicated in the color column by an empty dotted circle
. Second, you can explicitly override the color to use
for a block or a subtree. To do this, simply double click on the color column
next to the block of interest. This will pop up the color chooser dialog.
Explicitly overridden color for a block is indicated by a solid filled circle
icon filled with the selected color.
When an explicit color is set on a non-leaf node, all its children (and their
children) inherit that color unless explicitly overridden. For such nodes that
have a color inherited from their parent, we use the dotted-circle icon filled
with a pattern icon .
The second column reflects the opacity override for the blocks. Similar to
color, the opacity could be simply using value from the display properties
, or explicitly set
, or inhertied from parent node
.
Did you know?
In most cases with multiblock datasets, ParaView uses the vtkBlockColors
array for coloring. This is an array filled with random values so that each
block can be colored using a different color. That makes it easier to visually
see each of the blocks in the view. When in this mode,
the MultiblockInspector ‘s color column shows the color used for each of
the blocks using the same icon as the one used
for inherited colors i.e. .
You can change colors and opacities for a specific block by double clicking
on the corresponding icon. This allows setting values one at a time. For
specifying color and opacity overrides for multiple elements, you can select the
items and then right click to get the context menu. The context menu allows you
to change these properties for all the selected items, as shown in
Fig. 9.2.
Besides using the MultiblockInspector to set color and opacity overrides
for blocks, you can also directly changes these parameters from the
RenderView itself.
Simply right-click in the render view on the block of interest and
you’ll get a context menu, Fig. 9.3, that allows
changing the block properties and are more.
Context menu in RenderView can be used to change block display
properties.
Another useful feature with the MultiblockInspector is selection. If you
simply click on any row in the inspector, you will select the block (or
subtree) and the active view will highlight the selected block(s). Conversely,
if you make a block-based selection in the active
RenderView using ,
you will see the corresponding blocks highlighted
in the MultiblockInspector panel.
Explicit labeling and annotation of particular data values is often an important
element in data visualization and analysis. ParaView provides a variety of
mechanisms to enable annotation in renderings ranging from free floating text
rendered alongside other visual elements in the render view to data values
associated with particular points or cells.
Several types of text annotations can be added through the Sources >
Alphabetical menu. Text from these sources is drawn on top of 3D elements in
the render view. All annotation sources share some common properties under the
Display section of the Properties panel.
These include FontProperties such as the font to use, the size of the text, its color, opacity,
and justification, as well as text effects to apply such as making it bold,
italic, or shadowed.
Font property controls in annotation sources and filters.
There are three fonts available in ParaView: Arial, Courier, and Times. You can
also supply an arbitrary TrueType font file (*.ttf) to use by selecting the
File entry in the popup menu under FontProperties and clicking on the
... button to the right of the font file text field. A file selection
dialog will appear letting you choose a font file from the file system on which
paraview (or pvpython) is running.
The remaining display properties control where the text is placed in the render
view. There are two modes for placement, one that uses predefined positions
relative to the render view, and one that enables arbitrary interactive
placement in the render view. The first mode is active when the
UseWindowLocation checkbox is selected. It enables the annotation to be placed in one of
the four corners of the render view or centered horizontally at the top or
bottom of the render view. Buttons with icons representing the location are
shown in the Pipeline browser. These buttons correspond to locations in
the render view as depicted in Fig. 10.2.
Annotation placement buttons and where they place the annotation.
The second mode, activated by clicking the LowerLeftCorner checkbox, lets
you arbitrarily place the annotation. If the Interactivity property is
enabled, you can click and drag the annotation in the render view to place it,
or you can manually enter a location where the lower left corner of the
annotation’s bounding box should be placed. The coordinates are defined in terms
of fractional coordinates that range from [0, 1] in the x and y dimensions. The
coordinate system of the render view has a lower left origin, so a
LowerLeftCorner value of [0, 0] will place the annotation in the lower left corner
of the render view.
The Text source enables you to add a text annotation in the render view. It
has one property defining what text is displayed. Text can be multiline, and it
can contain numbers and unicode characters. Text may also contain Mathtex
expressions between starting and ending dollar signs. Mathtext expressions are a
subset of TeX math expressions [dt] . When Mathtext is used, the text
can only be on a single line.
An example of the Text source annotation in the upper left corner
with a math expression rendered from a Mathtext [dt] expression.
The AnnotateTime source is nearly identical to the Text source, but
it also offers access to the current time value set in ParaView. Control
over the format of the time display is available through the
Format property. This property takes a string with optional formatting sections
understood by the fmt library. By default, the value is “Time: {time:f}” where the “time” term
inside the curly braces is replaced with ParaView’s current time value, and the “:f” specifies that
it should be formatted as a float with six decimal digits. For other formatting
possibilities, please see the fmt syntax description at https://fmt.dev/latest/syntax.html.
Examples are near the bottom of that page.
The annotation sources described in the previous section are available for
adding text annotations that do not depend on any loaded datasets. To create
annotations that show values from an available data source in the
PipelineBrowser ,
several annotation filters are available. The properties available to
change the text font and annotation location are exactly the same as those
available for the annotation sources described in the previous section.
The AnnotateAttributeData makes it possible to create an annotation with
a data value from an array (or attribute) in a dataset. To use the filter, first
select the data array with the data of interest in the SelectInputArray .
These arrays may be point, cell, or field data arrays. The ElementId
property specifies the index of the point or cell whose value should be shown in
the annotation. If the selected input array is a field array (not associated
with points or cells), the ElementId specifies the tuple of the array to
show. When running in parallel, the ProcessId denotes the process that
holds the array from which the value should be obtained.
The Prefix text property precedes the attribute value in the rendered
annotation. There is no formatting string - the number is appended after the
prefix. If the array value selected is a scalar value, the annotation will
contain just the number. On the other hand, if the array value is from a
multicomponent array, the individual components will be added to the annotation
label in a space-separated list that is surrounded by parentheses.
Some file formats include the concept of globaldata, a single data value
stored in the data array for each time step. ParaView stores the set of such
data values as a field data array associated with the dataset with the same
number of values as timesteps. To display these global values in the render
view, use the AnnotateGlobalData filter.
The SelectArrays popup
menu shows the available field data arrays. The Prefix and Suffix
properties come before and after the data value in the annotation, respectively.
The Format property is a C language number format specifier as you would
use in a printf function call. The filter will provide a warning if the format
is invalid for the globaldata type.
A nice feature of ParaView is that it supports data sources that produce
different data at different times. Examples include file readers that read in
data for a requested time step and certain temporal filters. Each data source
advertises to ParaView the time values for which it can produce data. The data
produced and displayed in ParaView depends on the time you set in the ParaViewVCRControls or TimeInspector panel.
What is even nicer is that you can have several data sources that each advertise
and respond to a possibly unique set of times. That is, available sources do not
need to advertise that they support the same set of time points - in fact, they
may define data at entirely different time points. Given a requested
time, each data source will produce the data corresponding to the time it
supports closest to the requested time. This features makes it possible to
create animations from multiple datasets varying at different time resolutions,
for instance.
While the AnnotateTime source described earlier can be used to display
ParaView’s currently requested time, it does not show the time value to which a
particular data
source is responding. For example ParaView may be requesting data for time 5.0,
but if a source produces data for time values 10.0 and above, it will produce
the data for time 10.0, even though time 5.0 was requested. To show the time for
which a data source is producing data, you can instead use the
AnnotateTimeFilter .
Simply attach it to the source of interest. If several data sources are
present, a separate instance of this filter may be attached to each one.
Control over the format of the time display is available through the
Format property. The format string is a string supported by the fmt library
and defaults to “Time: {time:f}” where the “time” string inside the curly braces is
replaced by the currently loaded time value of the data source to which this filter
is attached. This filter also includes Shift and Scale properties used to
linearly transform the displayed time. The time value is first multiplied by the scale
and then the shift is then added to it.
If you want to display information about the environment in which a
visualization was generated, use the EnvironmentAnnotation filter. By
attaching this filter to a data source, you can have it automatically display
your user name on the system running ParaView, show which operating system was
used to generate it, present the date and time when the visualization was
generated, and show the file name of the source data if applicable. Each of
these items can be enabled or disabled by checkboxes in the Properties
panel for this filter.
If the input source for this filter is a file reader, the FileName
property is initialized to the name of the file. A checkbox labeled DisplayFullPath is available to show the full path of the file, but if unchecked,
only the file name will be displayed. This default file path can be overridden
by changing the text in the FileName property. If this filter is attached
to a filter instead of a reader, the file path will be initialized to an empty
string. It can be changed to the original file name manually, or an arbitrary
string if so desired.
The most versatile annotation filter, the PythonAnnotation filter,
offers the most general way of generating annotations that include information
about the dataset. Values from point, cell, field, and row data arrays may be
accessed and combined with mathematical operations in a short Python expression
defined in the Expression property. The type of data arrays available for use
in the Expression is set with the ArrayAssociation property.
Before going further, let’s look at an example of how to use the
PythonAnnotation filter.
Assume you want to show a data value at from a point array
named Pressure at point index 22.
First, set the ArrayAssociation to
PointData to ensure point data arrays can be referenced in the Python
annotation expression. To show the pressure value at point 22, set the
Expression property to
Pressure[22]
An example of a basic PythonAnnotation filter showing the value
of the Pressure array at point 22.
You can augment the Python expression to give the annotation more meaning. To
add a prefix, set the Expression to
'Pressure: %f'%(Pressure[22])
noindent All data arrays in the chosen association are provided as variables
that can be referenced in the expression as long as their names are valid Python
variables. Array names that are invalid Python variable names are available
through a modified version of the array name. This sanitized version of the
array name consists of the subset of characters in the array name that are
letters, numbers, or underscore (_) joined together without spaces in the
order in which they appear in the original array name. For example, an array
named VelocityX will be made available in the variable VelocityX .
Point and cell data in composite datasets such as multiblock datasets is
accessed somewhat differently than point or cell data in non-composite datasets.
The expression
Pressure[22]
retrieves a single scalar value from a point array in a non-composite
dataset, the same expression retrieves the 22nd element of the Pressure
array in each block. These values are held in a VTKCompositeDataArray, which is
a data structure that holds arrays associated with each block in the dataset.
Hence, when the expression
Pressure[22]
is evaluated on a composite dataset, the value returned and displayed
is actually an assemblage of array values from each block. To access the value
from a single block, the array from that block must be selected from the
Arrays member of the result VTKCompositeDataArray. To show the
Pressure value associated with 22nd point of block 2, for example, set the
expression to
Pressure[22].Arrays[2]
This expression yields a single data value in the rendered annotation, assuming
that the Pressure array has a single component. To show a range of array
values, use a Python range expression in the index into the Pressure field,
e.g.,
Pressure[22:24].Arrays[2]
This will show the Pressure values for points 22 and 23 from
block 2. You can also retrieve more than one array using an index range on the
Arrays member, e.g.,
Pressure[22:24].Arrays[2:5]
This expression evaluates to Pressure for points 22 and 23 for
blocks 2, 3, and 4.
The ArrayAssociation is really a convenience to make the set of data
arrays of the given association available as variables that can be used in the
Expression . The downside of using these array names is that arrays from
only one array association are available at a time. That means annotations that
require the combination of a cell data array and point data array, for example,
cannot be expressed with these convenience Python variables alone.
Fortunately, you can access any array in the input to this filter with a
slightly more verbose expression. For example, the following expression
multiplies a cell data value by a point data value:
Note that the arrays in the input are accessed in the above example
using their original array names.
In the example above, the expression inputs[0] refers to the first input to
the filter. While this filter can take only one input, it is based on the same
code used by the PythonCalculator (described in
Section 5.9.3), which puts its several inputs into a Python list,
hence the input to the PythonAnnotation filter is referenced as
inputs[0] .
In addition to making variables for the current array association available in
the expression, this filter provides some other variables that can be useful
when computing an annotation value.
points : Point locations (available for datasets with explicit points).
time_value , t_value : The current time value set in ParaView.
time_steps , t_steps : The number of timesteps available in the input.
time_range , t_range : The range of timesteps in the input.
time_index , t_index : The index of the current timestep in ParaView.
There are some situations where the variables above are not defined. If the
input has no explicitly defined points, e.g., image data, the points
variable is not defined. If the input does not define timesteps, the time_*
and t_* variables are not defined.
Finally, all the capabilities of the PythonCalculator, documented in Section 5.9.3,
are available, including the NumPy integration and access to the NumPy and SciPy methods.
Common Errors
The time-related variables are not needed to index into point or cell data arrays.
Only the point and cell arrays loaded for the current timestep are available in
the filter. You cannot access point or cell data from arbitrary timesteps from
within this filter.
With the capabilities in this filter, it is possible to reproduce the other
annotation sources and filters, as shown below.
Text source: To produce the text “My annotation”, write "Myannotation"
AnnotateTime source: To produce the equivalent of Time:{time:f}, write
"Time:%f"%time_value
AnnotateAttributeData filter: To produce the equivalent of setting
SelectInputArray to EQPS,
ElementId to 0
and ProcessId to 0, and Prefix
to Valueis:, write 'Valueis:%.12f'%(inputs[0].CellData['EQPS'][0]) .
AnnotateGlobalData filter: To produce the same annotation as setting
SelectArrays to KE, Prefix to Valueis: , Format to %7.5g,
and empty suffix, write "Valueis:%7.5g"%(inputs[0].FieldData['KE'].Arrays[0][time_index])
AnnotateTimeFilter : To produce the equivalent of setting Format to Time:%f,
Shift to 3, and Scale to 2, write "Time:%f"%(2*time_value+3) .
The examples above are meant to illustrate the versatility of the PythonAnnotation filter.
Using the specialized annotation sources and filters are
likely to be more convenient than entering the expressions in the examples.
Oftentimes, you want to render a reference grid in the backgroud for a
visualization – think axes in a chart view, except this time we are talking of the 3D
RenderView . Such a grid is useful to get an understanding for the data bounds and
placement in 3D space. In such cases, you use the AxesGrid . AxesGrid renders a 3D
grid with labels around the rendered scene. In this chapter, we will take a
closer look at using and customizing the AxesGrid .
To turn on the AxesGrid for a RenderView , you use the
Properties panel. Under the View section, you check the
AxesGrid checkbox to turn the AxesGrid on for the active view.
Clicking on the Edit button will pop up the AxesGrid
properties dialog ( Fig. 11.1)
that allows you to customize the AxesGrid . As with the Properties
panel, this is a searchable dialog, hence you can use the Search box at the
top of the dialog to search of properties of interest. At the same time, the
button can be used to toggle between default and
advanced modes for the panel.
Using this dialog, you can change common properties like the titles
( XTitle , YTitle , and ZTitle ),
title and label fonts using TitleFontProperties
and LabelFontProperties for each of the axes directions,
as well as the GridColor . Besides labelling the axes, you can render a
grid by checking ShowGrid . Once you have the AxesGrid setup to your
liking, you can use the to save your
selections so that they are automatically loaded next time you launch ParaView.
You can always use the to revert back to ParaView
defaults.
EditAxesGrid dialog is used to customize the AxesGrid .
To get a better look at the available customizations, let’s look at various
visualizations possible and then see how you can set those up using the
properties on the EditAxesGrid dialog. In these examples, we use the
disk_out_ref.ex2 example dataset packaged with ParaView.
In the images above, on the left is the default AxesGrid .
Simply turning on the visibility of the AxesGrid
will generate such a visualization. The axes places always stay behind the
rendered geometry even as you interact with the scene. As you zoom in and out,
the labels and ticks will be updated based on visual cues.
To show a grid along the axes planes, aligned with the ticks and labels, turn
on the ShowGrid checkbox, resulting in a visualization on the right.
By default, the gridded faces are always the farthest faces i.e. they stay behind
the rendered geometry and keep on updating as you rotate the scene. To fix which
faces of the bounding-box are to be rendered, use the FacesToRender
button (it’s an advanced property, so you may have to search for it using the
Seach box in the EditAxesGrid dialog). Suppose, we want to label
just one face, the lower XY face. In that case, uncheck all the other faces
except Min-XY in menu popped up on clicking on the FacestoRender
button. This will indeed just show the min-XY face, however as you rotate the
scene, the face will get hidden as soon as the face gets closer to the camera
than the dataset. This is because, by default, CullFrontfaces is enabled.
Uncheck CullFrontfaces and ParaView will stop removing the face as it
comes ahead of the geometry, enabling a visualization as follows.
Besides controlling which faces to render, you can also control where the labels
are placed. Let’s say we want ParaView to decide how to place labels along the Y
axis, however for the X axis, we want to explicitly label the values \(2.5\),
\(0.5\), \(-0.5\), and \(-4.5\). To that, assuming we are the advanced mode for the
EditAxesGrid panel,
check XAxisUseCustomLabels .
That will show a table widget that allows you to add values as shown below.
Using the button, add the custom values.
While at it, let’s also change the XAxisLabelFontProperties
and XAxisTitleFontProperties to change the color
to red and similar for the Y axis, let’s change the color to green. Increase the
title font sizes to 18, to make them stand out and you will get a visualization
as follows (below, left).
Here we see that both sides of the axis plane are
labeled. Suppose you only want to label one of the sides, in that case use the
AxesToLabel property to uncheck all but
Min-X and Min-Y . This
will result in the visualization shown above, right.
In pvpython, AxesGrid is accessible as the AxesGrid property on the
render view.
>>> renderView=GetActiveView()# AxesGrid property provides access to the AxesGrid object.>>> axesGrid=renderView.AxesGrid# To toggle visibility of the axes grid,>>> axesGrid.Visibility=1
All properties on the AxesGrid that you set using the EditAxesGrid
dialog are available on this axesGrid object and can be changed as follows:
Note you can indeed use the tracing capabilities described in
Section 1.6.2 to determine what Python API to use to change a
specific property on the EditAxesGrid dialog or use help .
>>> help(axesGrid)Help on GridAxes3DActor in module paraview.servermanager object:class GridAxes3DActor(Proxy) | GridAxes3DActor can be used to render a grid in a render view. | | Method resolution order: | GridAxes3DActor | Proxy | __builtin__.object | | Methods defined here: | | Initialize = aInitialize(self, connection=None, update=True) | | ---------------------------------------------------------------------- | Data descriptors defined here: | | AxesToLabel | Set the mask to select the axes to label. The axes labelled will be a subset of the | axes selected depending on which faces are also being rendered. | | CullBackface | Set to true to hide faces of the grid facing away from the camera i.e. hide all | back faces. | | CullFrontface | Set to true to hide faces of the grid facing towards from the camera i.e. hide all | front faces. | | DataPosition | If data is being translated, you can show the original data bounds for the axes | instead of the translated bounds by setting the DataPosition to match the | translation applied to the dataset. | ...
ParaView can be customized in a number of ways to tailor it to your
preferences and needs. Customization options include setting general
application behavior, customizing default property values used for filters,
representations, and views, and customizing aspects of the paraview client.
This chapter describes the different ways to customize ParaView.
As with any large application, paraview provides mechanisms to customize some
of its application behavior. These are referred to as application
settings . or just settings. Such settings can be changed using the Settings dialog,
which is accessed from the Edit > Settings menu (ParaView >
Preferences on the Mac). We have seen parts of this dialog earlier, e.g., in
Section 1.2,
Section 7.12.1, and Section 7.12.4. In
this section, we will take a closer look at some of the other options available
in this dialog.
The Settings dialog is split into several tabs. The General tab
consolidates most of the miscellaneous settings. The Camera tab enables you
to change the mouse interaction mappings for the RenderView and similar
views. The RenderView tab, which we saw earlier in Section 7.12.1
and Section 7.12.4, provides options in regards to rendering in
RenderView and similar views. The ColorPalette tab is used to change
the active color palette.
Using this dialog is not much different than the Properties panel. You have
the Search box at the top, which allows you to search properties matching
the input text ( Section 1.1.2). The
button can be used to toggle between default and
advanced modes.
To apply the changes made to any of the settings, use the Apply or OK
buttons. OK will apply the changes and close the dialog, while Cancel
will reject any changes made and close the dialog. Any changes made to
the options in this dialog are persistent across sessions. That is, the next time you
launch paraview, you’ll still be using the same settings chosen earlier. To
revert to the default, use the RestoreDefaults button. You can also manually
edit the setting file as in Section 12.2.3.
Furthermore, site maintainers can provide site-wide defaults for these, as is
explained in Section 12.2.4.
Next, we will see some of the important options available. Those that are only
available in the advanced mode are indicated as such using the
icon. You will either need to toggle on the
advanced options with the button or search for the
option using the Search box.
Settings dialog in paraview showing the General settings tab.
GeneralOptions
ShowWelcomeDialog : Uncheck this to not show the welcome screen at
application startup. You will need to restart paraview to see the effect.
ShowSaveStateOnExit : When this is checked paraview will prompt you
to save a state file when you exit the application.
CrashRecovery : When this is checked, paraview will intermittently
save a backup state file as you make changes in the visualization pipeline.
If paraview crashes for some reason, then when you relaunch paraview, it
will provide you with a choice to load the backup state saved before the crash
occurred. This is not \(100\%\) reliable, but some users may find it useful to
avoid losing their visualization state due to a crash.
ForceSingleColumnMenus : On platforms that support multicolumn menus,
ensure all menu items are selectable on low-resolution screens.
GUIFont
OverrideFont : When checked, use a custom font size for the user interface.
This overrides the system default font size.
FontSize : The size of the font to use for UI elements.
ViewOptions
DefaultViewType : When paraview starts up, it
creates RenderView by default. You can use this option to change the
type of the view that is created by default, instead of the RenderView .
You can even pick None if you don’t want to create any view by
default.
PropertiesPanelOptions
AutoApply : When checked, the Properties panel will
automatically apply any changes you make to the properties without requiring you
to click the Apply button. The same setting can also be toggled using the
button in the MainControls toolbar.
AutoApplyActiveOnly : This limits the auto-applying to the properties
on the active source alone.
PropertiesPanelMode :
This allows you to split the Properties
panel into separate panels as described in Section 1.2.
DataProcessingOptions
AutoConvertProperties : Several filters only work on one type of
array, e.g., point data arrays or cell data arrays. Before using such filters,
you are expected to apply the PointDataToCellData or CellDataToPointData filters. To avoid having to add these filters explicitly, you can
check this checkbox. When checked, ParaView will automatically convert data
arrays as needed by filters, including converting cell array to point arrays
and vice-versa, as well as extracting a single component from a
multi-component array.
Color/OpacityMapRangeOptions
TransferFunctionResetMode : This setting controls the initial
settings for how ParaView
will reset the ranges for color and opacity maps (or transfer functions). This
sets the initial value of the AutomaticRescaleRangeMode for newly created
color/opacity maps ( Section 3.2.2). This setting can
be changed on a per-color map basis after the color map has been created.
ScalarBarMode : This settings controls how paraview
manages showing the color legend (or scalar bar) in RenderView and
similar views.
DefaultTimeStep
Whenever a dataset with timesteps is opened, this setting controls how
paraview will update the current time shown by the application. You can choose
between Leavecurrenttimeunchanged,ifpossible, Gotofirsttimestep, and Gotolasttimestep.
Animation
CacheGeometryForAnimation : This enables caching of geometry when
playing animations to attempt to speed up animation playback in a loop. When
caching is enabled, data ranges reported by the Information panel and
others can be incorrect, since the pipeline may not have updated.
AnimationGeometryCacheLimit : When animation caching is enabled,
this setting controls how much geometry (in kilobytes) can be cached by any
rank. As soon as a rank’s cache size reaches this limit, ParaView will no
longer cache the remaining timesteps.
AnimationTimeNotation : Sets the display notation for the time in
the annotation toolbar. Options are Mixed , Scientific ,
and Fixed .
AnimationTimePrecision : Sets the number of digits displayed in the
time in the animation toolbar.
MaximumNumberofDataRepresentationLabels
When a selection is labeled by data attributes this is the maximum number of labels
to use. When the number of points/cells to label is above this value then a subset
of this many will be labeled instead. Too many overlapping labels becomes illegible,
so this is set to 100 by default.
Settings dialog in paraview showing the Camera settings tab.
This tab allows you to control how you can interact in RenderView and
similar views. Basically, you are setting up a mapping between each of the mouse
buttons and keyboard modifiers, and the available interaction types including
Rotate, Pan, Zoom, etc. The dialog allows you to set
the interaction mapping separately for 3D and 2D interaction modes
(see Section 4.4.2.2).
Settings dialog in paraview showing the ColorPalette settings tab.
The ColorPalette tab ( Fig. 12.3)
allows you to change the colors in the active color
palette. The tab lists the available color categories Surface ,
Foreground ,
Edges ,
Background ,
Text , and Selection . You
can manually set colors to use for each of these categories or load one of the
predefined palettes using the LoadPalette option. To understand
color palettes , let’s look at an example.
Let’s start paraview and split the active view to create two RenderView
instances side by side. You may want to start paraview with the -dr
command line argument to stop any of your current settings from interfering
with this demo. Next, show Sphere as Wireframe in the view
on the left, and show Cone as Surface in the view on the right.
Also, turn on CubeAxis for Cone . You will see something like
Fig. 12.4 (top).
The effect of loading the Print color palette as
the active palette. The top is the original visualization and the bottom shows the
result after loading the Print palette.
Now let’s say you want to generate an image for printing. Typically, for
printing, you’d want the background color to be white, while the wireframes and
annotations to be colored black. To do that, one way is to go change each of the
colors for each each of the views, displays and cube-axes. You can imagine how
tedious that will get especially with larger pipelines. Alternatively, using the
Settings dialog, change the active color palette to Print as shown in
Fig. 12.3 and then click OK or Apply .
The visualization will immediately change to something like
Fig. 12.4 (bottom).
Essentially, ParaView allows you to link any color property to one of
the color categories. When the color palette is changed, any color property
linked to a palette category will also be automatically updated to match the category color.
Fig. 12.5 shows how to link a color
property to a color palette category in the Properties panel. Use the tiny
drop-down menu marker to make the menu pop up that shows the color palette categories.
Select any one of them to link that property with the category. The link is
automatically severed if you manually change the color by simply clicking on the
button.
Popup menu allows you to link a color property to a color palette
category in the Properties panel.}
The section describes how to specify custom default settings for the
properties of sources, readers, filters, representations, and views.
This can be used to specify, for example, the default background color
for new views, whether a gradient background should be used, the
resolution of a sphere source, which data arrays to load from a
particular file format, and the default setting for almost any other
object property.
The same custom defaults are used across all the ParaView
executables. This means that custom defaults specified in the
paraview executable are also used as defaults in
pvpython and pvbatch, which makes it easier
to set up a visualization with paraview and use
pvpython or pvbatch to generate an animation
from time-series data, for example.
The Properties panel in paraview has three sections,
Properties ,
Display , and View . Each section has two
buttons. These buttons are circled in red in
Fig. 12.6. The button with the disk
icon is used to save the current property values in that section that
have been applied with the Apply button. Property values that
have been changed but not applied with the Apply button will not
be saved as custom default settings.
The button with the circular arrow (or reload icon) is used to restore
any custom property settings for the object to ParaView’s application
defaults. Once you save the current property settings as defaults, those
values will be treated as the defaults from then on until you change
them to another value or reset them. The saved defaults are written to
a configuration file so that they are available when you close and
launch ParaView again.
Buttons for saving and restoring default property values in the Properties panel.
You can undo your changes to the default property values by clicking
on the reload button. This will reset the current view property values
to paraview’s application defaults. To fully restore
paraview’s default values, you need to click the save
button again. If you don’t, the restored default values will be
applied only to the current object, and new instances of that object
will have the custom default values that were saved the last time you
clicked the save button.
Suppose you want to change the default background color in the
RenderView . To do this, scroll down to the View section of
the Properties panel and click on the combo box that shows the
current background color. Select a new color, and click OK . Next,
scroll up to the View(RenderView) section header and click on
the disk button to the right of the header. This will save the new
background color as the default background color for new views. To see
this, click on the + sign next to the tab above the 3D view to
create a new layout. Click on the RenderView button. A new
render view will be created with the custom background color you just
saved as default.
Custom default settings are stored in a text file in the JSON
format. We recommend to use the user interface
in paraview to set most default values, but it is
possible to set them by editing the JSON settings file directly. It is
always a good idea to make a backup copy of a settings file prior to
manual editing.
The ParaView executables read from and write to a file named
ParaView-UserSettings.json, which is located in your home
directory on your computer. On Windows, this file is located at
%APPDATA%/ParaView/ParaView-UserSettings.json, where the
APPDATA environment variable is usually something like
C:/Users/USERNAME/AppData/Roaming, where USERNAME is
your login name. On Unix-like systems, it is located under
~/.config/ParaView/ParaView-UserSettings.json. This file will
exist if you have made any default settings changes through the user
interface in the paraview executable. Once set, these
default settings will be available in subsequent versions of ParaView.
A simple example of a file that specifies custom default settings is
shown below:
Note the hierarchical organization of the file. The first level of the
hierarchy specifies the group to which the object whose settings are
being specified refers (“sources” in this example). The second level
names the object whose settings are being specified. Finally, the
third level specifies the custom default settings themselves. Note
that default values can be set to literal numbers, strings, or arrays
(denoted by comma-separated literals in square brackets).
The names of groups and objects come from the XML proxy definition
files in ParaView’s source code in the directory
ParaView/ParaViewCore/ServerManager/SMApplication/Resources
(ParaView\ParaViewCore\ServerManager\SMApplication\Resources on Windows systems) . The
group name is defined by the name attribute in a
ProxyGroup element. The object name comes from the
name attribute in the Proxy element (or elements of
vtkSMProxy subclasses). The property names come from the
name attribute in the *Property XML elements for the
object.
Did you know?
The application-wide settings available in paraview
through the Edit > Settings menu are also saved to this user
settings file. Hence, if you have changed the application settings,
you will see some entries under a group named “settings”.
In addition to individual custom default settings, ParaView offers a
way to specify site-wide custom default settings for a ParaView
installation. These site-wide custom defaults must be defined in a
JSON file with the same structure as the user settings file. In fact,
one way to create a site settings file is to set the custom defaults
desired in paraview, close the program, and then copy the
user settings file to the site settings file. The site settings file
must be named ParaView-SiteSettings.json.
The ParaView executables will search for the site settings file in
several locations. If you installed ParaView in the directory
INSTALL, then the ParaView executables will search for the
site settings file in these directories in the specified order:
INSTALL/share/paraview-X.Y ( INSTALLshareparaview-X.Y in Windows systems)
INSTALL/lib (INSTALLlib in Windows systems)
INSTALL
INSTALL/.. (INSTALL/lib in Windows systems)
where X is ParaView’s major version number and Y is
the minor version number. ParaView executables will search these
directories in the given order, reading in the first
ParaView-SiteSettings.json file it finds. The conventional
location for this kind of configuration file is in the share
directory (the first directory searched), so we recommend placing the
site settings file there.
Custom defaults in the user settings file take precedence over custom
defaults in the site settings. If the same default is specified in
both the ParaView-SiteSettings.json file and
ParaView-UserSettings.json file in a user’s directory, the
default specified in the ParaView-UserSettings.json file will
be used. This is true for both object property settings and
application-settings set through the Edit > Settings menu.
To aid in debugging problems with the site settings file location, you
can define an evironment variable named PV_SETTINGS_DEBUG
to something other than an empty string. This will turn on verbose
output showing where the ParaView executables are looking for the site
settings file.
Tutorials are split in Self-directed Tutorials and Classroom Tutorials:
Self-directed Tutorial’s Section 1 to
Section 5 provide an introduction to the ParaView software and its history,
and exercises on how to use ParaView that cover basic usage, batch python scripting and visualizing large models.
Classroom Tutorials’s Section 1 to Section 18 provide
beginning, advanced, python and batch, and targeted tutorial lessons on how to use ParaView that are presented
as a 3-hour class internally within Sandia National Laboratories.
Self-directed Tutorial provides an introduction to the ParaView software and its history,
and exercises on how to use ParaView that cover basic usage, batch python scripting and visualizing large models.
This tutorial was created by Kenneth Moreland at Sandia National Laboratories, has written guidance and background
and can be followed independently.
Thanks to Amy Squillacote, David DeMarle, and W. Alan Scott for
contributing material to this tutorial. And, of course, thanks to everyone
at Kitware, Sandia National Laboratories, Los Alamos National Laboratory,
and all other contributing organizations for their hard work in making
ParaView what it is today.
This work was supported by the Director, Office of Advanced Scientific
Computing Research, Office of Science, of the U.S. Department of Energy
under Contract No. 12-015215, through the Scientific Discovery through
Advanced Computing (SciDAC) Institute of Scalable Data Management,
Analysis and Visualization.
This work is licensed under the Creative Commons Attribution 4.0 International License.
To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ or
send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering
Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of
Energy’s National Nuclear Security Administration under contract DE-NA-0003525.
ParaView is an open-source application for visualizing two- and three-dimensional
data sets. The size of the data sets ParaView can handle varies widely
depending on the architecture on which the application is run. The
platforms supported by ParaView range from single-processor workstations
to multiple-processor distributed-memory supercomputers or workstation
clusters. Using a parallel machine, ParaView can process very large data
sets in parallel and later collect the results. To date, ParaView has
been demonstrated to process billions of unstructured cells and to
process over a trillion structured cells. ParaView’s parallel framework
has run on over 100,000 processing cores.
ParaView’s design contains many conceptual features that make it stand
apart from other scientific visualization solutions.
An open-source, scalable, multi-platform visualization application.
Support for distributed computation models to process large data sets.
An open, flexible, and intuitive user interface.
An extensible, modular architecture based on open standards.
A flexible BSD 3-clause license.
Commercial maintenance and support.
ParaView is used by many academic, government, and commercial
institutions all over the world. ParaView’s open license makes it
impossible to track exactly how many users ParaView has, but it is
thought to be many thousands large based on indirect evidence. For
example, ParaView is downloaded roughly 100,000 times every year.
ParaView also won the HPCwire Readers’ Choice Award in 2010 and 2012 and
HPCwire Editors’ Choice Award in 2010 for Best HPC Visualization Product
or Technology.
ZSU23-4 Russian Anti-Aircraft vehicle being hit by a planar wave. Image courtesy of Jerry Clarke, US Army Research Laboratory.
A loosely coupled SIERRA-Fuego-Syrinx-Calore simulation with 10 million unstructured hexahedra cells of objects-in-crosswind fire.
Simulation of a Pelton turbine. Image courtesy of the Swiss National Supercomputing Centre.
Airflow around a Le Mans Race car. Image courtesy of Renato N. Elias, NACAD/COPPE/UFRJ, Rio de Janerio, Brazil.
As demonstrated in these visualizations, ParaView is a general-purpose
tool with a wide breadth of applications. In addition to scaling from
small to large data, ParaView provides many general-purpose
visualization algorithms as well as some specific to particular
scientific disciplines. Furthermore, the ParaView system can be extended
with custom visualization algorithms.
The application most people associate with ParaView is really just a
small client application built on top of a tall stack of libraries that
provide ParaView with its functionality. Because the vast majority of
ParaView features are implemented in libraries, it is possible to
completely replace the ParaView GUI with your own custom application.
Furthermore, ParaView comes with a
application that allows you to automate the visualization and
post-processing with Python scripting.
Available to each ParaView application is a library of user interface
components to maximize code sharing between them. A library provides the
abstraction layer necessary for running parallel, interactive
visualization. It relieves the client application from most of the
issues concerning if and how ParaView is running in parallel.
The Visualization Toolkit (VTK)
provides the basic visualization and rendering algorithms. VTK
incorporates several other libraries to provide basic functionalities
such as rendering, parallel processing, file I/O, and parallel
rendering. Although this tutorial demonstrates using ParaView through
the ParaView client application, be aware that the modular design of
ParaView allows for a great deal of flexibility and customization.
The ParaView project started in 2000 as a collaborative effort between
Kitware Inc. and Los Alamos National Laboratory. The initial funding was
provided by a three year contract with the US Department of Energy ASCI
Views program. The first public release, ParaView 0.6, was announced in
October 2002. Development of ParaView continued through collaboration of
Kitware Inc. with Sandia National Laboratories, Los Alamos National
Laboratories, the Army Research Laboratory, and various other academic
and government institutions.
In September 2005, Kitware, Sandia National Labs and CSimSoft started
the development of ParaView 3.0. This was a major effort focused on
rewriting the user interface to be more user friendly and on developing
a quantitative analysis framework. ParaView 3.0 was released in May
2007.
Since this time, ParaView development continues. ParaView 4.0 was
released in June 2013 and introduced more cohesive GUI controls and
better multiblock interaction. Subsequent releases also include the
Catalyst library for in situ integration into simulation and other
applications. ParaView 5.0 was released in January 2016 and provided a
major update to the rendering system. The new rendering takes advantage
of OpenGL 3.2 features to provide huge performance improvements.
Subsequent releases also added support for ray cast rendering with the
OSPRay library.
Development of ParaView continues today. Sandia National Laboratories
continues to fund ParaView development through the ASC project. ParaView
is part of the SciDAC Scalable Data Management, Analysis, and
Visualization (SDAV) Institute Toolkit
https://sdav-scidac.org. The US Department of
Energy also funds ParaView through Los Alamos National Laboratories and
various SBIR projects and other contracts. The US National Science
Foundation also often funds ParaView through SBIR projects. Other
institutions also have ParaView support contracts: Electricity de
France, Mirarco, and oil industry customers. Also, because ParaView is
an open source project, other institutions such as the Swiss National
Supercomputing Centre contribute back their own development.
Put simply, the process of visualization is taking raw data and
converting it to a form that is viewable and understandable to humans.
This allows us to get a better cognitive understanding of our data.
Scientific visualization is specifically concerned with the type of data
that has a well defined representation in 2D or 3D space. Data that
comes from simulation meshes and scanner data is well suited for this
type of analysis.
There are three basic steps to visualizing your data: reading,
filtering, and rendering. First, your data must be read into ParaView.
Next, you may apply any number of filters that process the data to generate,
extract, or derive features from the data. Finally, a viewable image is
rendered from the data.
ParaView was designed primarily to handle data with spatial
representation. Thus the primary data types used in ParaView are meshes.
Uniform Rectilinear (Image Data)
A uniform rectilinear grid is a one- two-
or three- dimensional array of data. The
points are orthonormal to each other and
are spaced regularly along each direction.
Non-uniform Rectilinear (Rectilinear Grid)
Similar to the uniform rectilinear grid
except that the spacing between points may
vary along each axis.
Curvilinear (Structured Grid)
Curvilinear grids have the same topology as
rectilinear grids. However, each point in a
curvilinear grid can be placed at an arbitrary
coordinate (provided that it does not
result in cells that overlap or self intersect).
Curvilinear grids provide the more compact
memory footprint and implicit topology of
the rectilinear grids, but also allow for much
more variation in the shape of the mesh.
Polygonal (Poly Data)
Polygonal data sets are composed of points,
lines, and 2D polygons. Connections between
cells can be arbitrary or non-existent.
Polygonal data represents the basic rendering
primitives. Any data must be converted
to polygonal data before being rendered
(unless volume rendering is employed),
although ParaView will automatically make
this conversion.
Unstructured Grid
Unstructured data sets are composed of
points, lines, 2D polygons, 3D tetrahedra,
and nonlinear cells. They are similar to
polygonal data except that they can also
represent 3D tetrahedra and nonlinear cells,
which cannot be directly rendered.
In addition to these basic data types, ParaView also supports multiblock data. A
basic multi-block data set is created whenever data sets are grouped
together or whenever a file containing multiple blocks is read. ParaView
also has some special data types for representing Hierarchical Adaptive
Mesh Refinement (AMR), Hierarchical Uniform AMR, Octree, Tabular,
and Graph type data sets.
There are many places to find more information about ParaView. The
manual, titled The ParaView Guide, is available for purchase as a hard
copy or can be downloaded for free from https://docs.paraview.org/.
The ParaView web page, https://www.paraview.org/,
is also an excellent place to find more information about ParaView. From
there you can find helpful links to the ParaView Discourse forum, Wiki
pages, and frequently asked questions as well as information about
professional support services.
ParaView’s menu is a good place to start to find useful information and
contains many links to documentation and training materials. The menu
has entries that directly bring up the aforementioned ParaView Guide
and web pages. The menu also provides several training materials
including a quick Getting Started with ParaView guide, multiple
tutorials (including this one), and some example visualizations.
Let us get started using ParaView. In order to follow along, you will
need your own installation of ParaView. If you do not already have ParaView,
you can download a copy from https://www.paraview.org/Download/.
ParaView launches like most other applications. On Windows, the
launcher is located in the start menu. On Macintosh, open the
application bundle that you installed. On Linux, execute paraview from a command
prompt (you may need to set your path).
The examples in this tutorial rely on some data that is included
with the binary distribution of ParaView starting with version 5.2.
For earlier versions, the tutorial data are available at
https://www.paraview.org/Wiki/The_ParaView_Tutorial. You may install
this data into any directory that you like, but make sure that you can
find that directory easily. Any time the tutorial asks you to load a
file it will be from the directory you installed this data in.
The ParaView GUI conforms to the platform on which it is running, but on
all platforms it behaves basically the same. The layout shown here is
the default layout given when ParaView is first started. The GUI
comprises the following components.
Menu Bar
As with just about any other program, the menu bar allows you to
access the majority of features.
Toolbars
The toolbars provide quick access to the most commonly used features
within ParaView.
Pipeline Browser
ParaView manages the reading and filtering of data with a pipeline.
The pipeline browser allows you to view the pipeline structure and
select pipeline objects. The pipeline browser provides a convenient
list of pipeline objects with an indentation style that shows the
pipeline structure.
Properties Panel
The properties panel allows you to view and change the parameters of
the current pipeline object. On the properties panel is an advanced
properties toggle that shows and hides advanced controls. The
properties are by default coupled with an Information tab that shows a basic
summary of the data produced by the pipeline object.
3D View
The remainder of the GUI is used to present data so that you may
view, interact with, and explore your data. This area is initially
populated with a 3D view that will provide a geometric representation
of the data.
Note that the GUI layout is highly configurable, so that it is easy to
change the look of the window. The toolbars can be moved around and even
hidden from view. To toggle the use of a toolbar, use the View → Toolbars
submenu. The pipeline browser and properties panel are both dockable
windows. This means that these components can be moved around in the GUI,
torn off as their own floating windows, or hidden altogether. These two
windows are important to the operation of ParaView, so if you hide them
and then need them again, you can get them back with the View menu.
There are two ways to get data into ParaView: read data from a file or
generate data with a source object. All sources are located in the
Sources menu. Sources can be used to add annotation to a view, but they
are also very handy when exploring ParaView’s features.
(Creating a Source)
Let us start with a simple one. Go to the Sources
menu, open the Geometric Shapes submenu, and select Cylinder. Once you
select the Cylinder item you will notice that an item named Cylinder1
is added to and selected in the pipeline browser. You will also notice
that the properties panel is filled with the properties for the
cylinder source. Click the Apply button to accept the default
parameters.
Once you click Apply, the cylinder object will be displayed in the 3D
view window on the right.
Now that we have created our first simple visualization, we want to
interact with it. There are many ways to interact with a visualization
in ParaView. We start by exploring the data in the 3D view.
(Interacting with a 3D View)
This exercise is a continuation of Exercise 2.1.
You will need to finish that exercise before beginning this one.
You can manipulate the cylinder in the 3D view by dragging the mouse
over the 3D view. Experiment with dragging different mouse buttons—left,
middle, and right—to perform different rotate, pan, and zoom operations.
Also try using the buttons in conjunction with the shift and ctrl
modifier keys. Additionally you can hold down the x, y, or z key while
you drag the mouse to constrain movement along the x, y, or z axis.
ParaView contains a couple of toolbars to help with camera
manipulations. The first toolbar, the Camera Controls toolbar, shown
here, provides quick access to particular camera views. The leftmost
button performs a reset camera such that it maintains
the same view direction but repositions the camera such that the entire
object can be seen. The second button performs a
zoom to data. It behaves very much like reset camera except that
instead of positioning the camera to see all data, the camera is placed
to look specifically at the data currently selected in the pipeline
browser. The third button performs a
reset camera closest such that it maximizes the occupation,
in the screen, of the whole scene bounding box. The fourth button
performs a zoom closest to data. It behaves
very much like reset camera closest except that instead of positioning
the camera to see all data, the camera is placed to look specifically
at the data currently selected in the pipeline browser. You currently
only have one object in the pipeline browser, so right now reset camera
and zoom to data, and reset camera closest and zoom closest to data will
perform the same operation.
The next button in the camera controls toolbar allows
you to select a rectangular region of the screen to zoom to (a rubber-band zoom).
The following six buttons, starting with , reposition the camera to view
the scene straight down one of the global coordinate’s axes in either
the positive or negative direction. The rightmost two buttons rotate the view either clockwise or counterclockwise. Try
playing with these controls now.
The second toolbar controls the location of the center of rotation and
the visibility of the orientation axes. The rightmost button
allows you to pick the center of rotation. Try clicking that button then
clicking somewhere on the cylinder. If you then drag the left button in
the 3D view, you will notice that the cylinder now rotates around this
new point. The next button to the left replaces the center
of rotation to the center of the object. The next button to the left
shows or hides axes drawn at the center of rotation. (You probably will not notice
the effects when the center of rotation is at the center of the cylinder
because the axes will be hidden by the cylinder. Use the pick center of
rotation again and you should be able to see the effects.)
The final leftmost button toggles showing the
orientation axes, the always-viewable axes in the lower left corner
of the 3D view.
Although interactive 3D controls are a vital part of visualization, an
equally important ability is to modify the parameters of the data
processing and display. ParaView contains many GUI components for
modifying visualization parameters, which we will begin to explore in
the next exercise.
(Modifying Visualization Parameters)
This exercise is a continuation of Exercise 2.2.
You will need to finish that exercise before beginning this one.
You surely noticed that ParaView creates not a real cylinder but rather
an approximation of a cylinder using polygonal facets. The default
parameters for the cylinder source provide a very coarse approximation
of only six facets. (In fact, this object looks more like a prism than a
cylinder.) If we want a better representation of a cylinder, we can
create one by increasing the Resolution parameter. The Resolution
parameters, like all other parameters for the cylinder object, are
located in the properties panel under the button when the cylinder
object is selected in the pipeline browser.
Using either the slider or text edit, increase the resolution to 50 or
more. Notice that the Apply button become colored again. This is because
changes you make to the object properties are not immediately enacted.
The highlighted button is a reminder that the parameters of one or more
pipeline objects are “out of sync” with the data that you are viewing.
Hitting the Apply button will accept these changes whereas hitting the
Reset button will revert the options back to the last time they
were applied. Hit the Apply button now. The resolution is changed so that
it is virtually indistinguishable from a true cylinder.
If your work has you creating cylinder sources frequently and you find
yourself modifying Resolution or other parameters to some value other
than the default each time, you can save your preferred default
parameters by hitting the save parameters button . Once you hit the
button, ParaView will remember your preferences for objects of
that type and use those parameters when you create future objects. Conversely,
if you have changed the parameters and want to reset them to the “factory
default,” you can click the restore parameters button . As we will
see in future exercises, we can have multiple visualization objects open at
once. To copy parameters from one object to another, use the copy and
paste parameters buttons.
If you scroll down the properties panel, you will notice a set of
Display properties. Try these options now by clicking on the Edit
button under Coloring to select a new color for the cylinder. (This
button is also replicated in the toolbar.) You may notice that you do
not need to hit Apply for display properties.
If you scroll down further yet to the bottom of the properties panel,
you will notice a set of View properties. Use the view properties to
turn on the Axes Grid.
By default many of the lesser used display properties are hidden. The
advanced properties toggle can be used to show or hide these extra
parameters. There is also a search box at the top of the properties
panel that can be used to quickly find a property. Try typing specular
into this search box now. Under the display properties you should see an
option named Specular. This controls the intensity of the specular
highlight seen on shiny objects. Set this parameter to 1 to make the
cylinder shiny.
Most objects have similar display and view properties. Here are some
other common tricks you can do with most objects using parameters
available in the properties panel and that you can try now.
Show 3D axes at the borders of the object containing rulers showing
the physical distance in each direction by clicking the Axes Grid
checkbox under the View options.
Make objects transparent by changing their Opacity parameter. An
opacity parameter of 1 is completely opaque, a parameter of 0 is
completely invisible, and values in between are varying degrees of
see through.
From the previous exercises you have noted that some visualization
operations (but not all) require pressing the Apply button before seeing
the effect of the change. This apply button serves an important
function. When visualizing large data, which ParaView is designed to do,
simple actions like creating an object or changing a parameter can take
a long time. Thus this two phased approach allows you to establish all
the visualization parameters for a particular action before enacting an
operation (by hitting Apply). However, when dealing with small data,
operations complete near instantaneously, so the process of hitting
Apply becomes redundant. In these cases, you may wish to turn on auto
apply.
(Toggle Auto Apply)
Find the auto apply button in the top toolbar.
This is a toggle button. Click it now and note that it stays depressed.
While auto apply is on, it is no longer necessary to hit the Apply
button. Try changing the Resolution of the cylinder source as you did in
Exercise 2.3 (or create a new source if your
cylinder is no longer available). Note that as soon as you make the change,
the visualization is updated.
You can turn off auto apply by clicking the toolbar button again.
You can complete the rest of these exercises with auto apply either on or
off. The instructions will assume that auto apply is off and prompt you
to hit the Apply button. If you have auto apply on, ignore these
instructions.
As you would expect, ParaView allows you to control the color of many
elements. In many cases the changing the color of one element
necessitates the changing of another. For example, if changing the
background to a light color, it is important to change text on that
background to a dark color. Otherwise the text will be unreadable. To
help manage sets of interdependent colors, ParaView supports the idea of
color palettes. You can easily change the view’s color palette using the
load color palette button in the toolbar.
(Changing the Color Palette)
Make sure the orientation axes is shown in the lower left corner.
This is toggled with the button as described
in Exercise 2.2. Note that the orientation axis has
the labels “X,” “Y,” and “Z.”
Find the load color palette button in the top toolbar. Click that button
to get a pull down menu of available palettes. Experiment with different
palettes. Observe that both the background color and the labels in the
orientation axes change.
The colors used for the color palettes are part of ParaView’s settings.
You can see and set all of these colors in the Edit
→ Settings (ParaView → Preferences
on the Mac) under the Color Palette tab. You can also get to the color
palette settings by clicking on the color palette button and
selecting the Edit Current Palette… button.
Now is a good time to note the undo and redo buttons in the toolbar.
Visualizing your data is often an exploratory process, and it is often
helpful to revert back to a previous state. You can even undo back to
the point before your data were created and redo again.
(Undo and Redo)
Experiment with the undo and redo buttons. If you have not done so,
create and modify a pipeline object like what is done in Exercise 2.1.
Watch how parameter changes can be reverted and restored. Also notice how whole
pipeline objects can be destroyed and recreated.
There are also undo camera and redo camera buttons at the view’s
toolbar. These allow you to go back and forth between camera angles that
you have made so that you do not have to worry about errant mouse
movements ruining that perfect view. Move the camera around and then use
these buttons to revert and restore the camera angle.
We are done with the cylinder source now. We can delete the pipeline
object by making sure the cylinder is selected in the pipeline browser
and hitting delete in the properties panel.
Now that we have had some practice using the ParaView GUI, let us load
in some real data. As you would expect, the Open command is the first
one off of the File menu, and there is also toolbar button for opening
a file. ParaView currently supports about 220 distinct file formats, and
the list grows as more types get added. To see the current list of
supported files, invoke the Open command and look at the list of files
in the Files of type chooser box.
ParaView’s modular design allows for easy integration of new VTK readers
into ParaView. Thus, check back often for new file formats. If you are
looking for a file reader that does not seem to be included with
ParaView, check in with the ParaView mailing list
(paraview@paraview.org). There are many file readers included with VTK
but not exposed within ParaView that could easily be added. There are
also many readers created that can plug into the VTK framework but have
not been committed back to VTK; someone may have a reader readily
available that you can use.
(Opening a File)
Let us open our first file now. Click the Open
toolbar button (or menu item) . Note that ParaView uses a custom file
browser, which provides several convenience features. On the left side
of the file browser dialog are a pair of boxes containing lists of
directories, which provide quick access to files in common
directories. The top left list contains a list of common data
directories on your system. The bottom left list, which is initially
empty, is filled with directories from which you have recently loaded
files. Double click on the Examples directory listed in the top left
box. This is a directory created by the ParaView installation that
contains the files we use in this tutorial.
Open the file disk_out_ref.ex2. Note that opening a file is a two step
process, so you do not see any data yet. Instead, you see that the
properties panel is populated with several options about how we want to
read the data.
Click the checkbox in the header of the block arrays list to turn on the
loading of all the block arrays. This is a small data set, so we do not
have to worry about loading too much into memory. Once all of the
variables are selected, click to load all of the data. When the data are
loaded you will see that the geometry looks like a cylinder with a
hollowed out portion in one end. These data are the output of a
simulation for the flow of air around a heated and spinning disk. The
mesh you are seeing is the air around the disk (with the cylinder shape
being the boundary of the simulation). The hollow area in the middle is
where the heated disk would be were it meshed for the simulation.
Most of the time ParaView will be able to determine the appropriate
method to read your file based on the file extension and underlying
data, as was the case in Exercise 2.7. However, with so
many file formats supported by ParaView there are some files that cannot
be fully determined. In this case, ParaView will present a dialog box
asking what type of file is being loaded. The following image is an
example from opening a netCDF file, which is a generic file format for
which ParaView has many readers for different conventions.
Before we continue on to filtering the data, let us take a quick look at
some of the ways to represent the data. The most common parameters for
representing data are located in a pair of toolbars. (They can also be
found in the Display group of the properties panel.)
(Representation and Field Coloring)
Play with the data representation a bit. Make sure disk_out_ref.ex2 is
selected in the pipeline browser. (If you do not have the data loaded, repeat
Exercise 2.7.) Use the variable chooser to color the surface by
the pres variable. To see the structure of the mesh, change the representation
to Surface With Edges. You can view both the cell structure and the interior
of the mesh with the Wireframe representation.
We have now successfully read in some data and gleaned some information
about it. We can see the basic structure of the mesh and map some data
onto the surface of the mesh. However, as we will soon see, there are
many interesting features about these data that we cannot determine by
simply looking at the surface of these data. There are many variables
associated with the mesh of different types (scalars and vectors). And
remember that the mesh is a solid model. Most of the interesting
information is on the inside.
We can discover much more about our data by applying filters.
Filters are functional units that process the data to generate, extract,
or derive features from the data. Filters are attached to readers,
sources, or other filters to modify its data in some way. These filter
connections form a visualization pipeline. There is a great amount
of filters available in ParaView. Here are the most common, which are
all available by clicking on the respective icon in the filters toolbar.
Calculator
Evaluates a user=defined expression on a per=point or per-cell basis.
Contour
Extracts the points, curves, or surfaces where a scalar field is
equal to a user-defined value. This surface is often also called an
isosurface.
Clip
Intersects the geometry with a half space. The effect is to remove
all the geometry on one side of a user-defined plane.
Slice
Intersects the geometry with a plane. The effect is similar to
clipping except that all that remains is the geometry where the plane
is located.
Threshold
Extracts cells that lie within a specified range of a scalar field.
Extract Subset
Extracts a subset of a grid by defining either a volume of interest
or a sampling rate.
Glyph
Places a glyph, a simple shape, on each point in a mesh. The
glyphs may be oriented by a vector and scaled by a vector or scalar.
Stream Tracer
Seeds a vector field with points and then traces those seed points
through the (steady state) vector field.
Warp (vector)
Displaces each point in a mesh by a given vector field.
Group Datasets
Combines the output of several pipeline objects into a single multi
block data set.
Extract Level
Extract one or more items from a multi block data set.
These eleven filters are a small sampling of what is available in
ParaView. In the Filters menu are a great many more filters that you can
use to process your data. ParaView currently exposes more than one
hundred filters, so to make them easier to find the Filters menu is
organized into submenus.
These submenus are organized as follows.
Recent
The list of most recently used filters sorted with the most recently
used filters on top.
Favorites
The list includes your favorites filters.
Alphabetical
An alphabetical listing of all the filters available. If you are not
sure where to find a particular filter, this list is guaranteed to
have it. There are also many filters that are not listed anywhere but
in this list.
AMR
A set of filters designed specifically for data in an adaptive mesh
refinement (AMR) structure.
Annotation
Filters that add annotation (such as text information) to the
visualization.
CTH
Filters used to process results from a CTH simulation.
Chemistry
This contains filters for chemistry related datasets.
Common
The most common filters. This is the same list of filters available
in the filters toolbar and listed previously.
CosmoTools
This contains filters developed at LANL for cosmology research.
Data Analysis
The filters designed to retrieve quantitative values from the data.
These filters compute data on the mesh, extract elements from the
mesh, or plot data.
Hyper Tree Grid
This contains filters for hyper-tree grid datasets.
Material Analysis
Filters for processing data from volume fractions of materials.
Point Interpolation
Filters that take an unstructured collection of points in space
without cells connecting them and estimate the field interpolation
between them.
Quadrature Points
Filters to support simulation data given as integration points that
can be used for numerical integration with Gaussian quadrature.
Statistics
This contains filters that provide descriptive statistics of data,
primarily in tabular form.
Temporal
Filters that analyze or modify data that changes over time. All
filters can work on data that changes over time because they are
executed on each time snapshot. However, filters in this category
will retrieve the available time extents and examine how data changes
over time.
Searching through these lists of filters, particularly the full
alphabetical list, can be cumbersome. To speed up the selection of
filters, you should use the quick launch dialog. Pressing the ctrl
and space keys together on Windows or Linux or the alt and space keys
together on Macintosh, ParaView brings up a small, lightweight dialog
box like the one shown here.
Type in words or word fragments that are contained in the filter name,
and the box will list only those sources and filters that match the
terms. Hit enter to add the object to the pipeline browser. Press Esc a
couple of times to cancel the dialog.
You have probably noticed that some of the filters are grayed out. Many
filters only work on a specific types of data and therefore cannot
always be used. ParaView disables these filters from the menu and
toolbars to indicate (and enforce) that you cannot use these filters.
Throughout this tutorial we will explore many filters. However, we
cannot explore all the filters in this forum. Consult the Filters Menu
chapter of ParaView’s on-line or built-in help for more information on
each filter.
(Apply a Filter)
Let us apply our first filter. If you do not have
the disk_out_ref.ex2 data loaded, do so now (Exercise 2.7).
Make sure that disk_out_ref.ex2 is selected in the pipeline browser and
then select the contour filter from the filter toolbar or Filters
menu. Notice that a new item is added to the pipeline filter underneath
the reader and that the properties panel updates to the parameters of
the new filter. As with reading a file, applying a filter is a two step
process (unless auto apply is enabled). After creating the filter you
get a chance to modify the parameters (which you will almost always
do) before applying the filter.
We will use the contour filter to create an isosurface where the
temperature is equal to 400 K. First, change the Contour By parameter to
the temp variable. Then, change the isosurface value to 400. Finally,
hit . You will see the isosurface appear inside of the volume. If
disk_out_ref.ex2 was still colored by pressure from Exercise 2.8,
then the surface is colored by pressure to match.
In the preceding exercise, we applied a filter that processed the data
and gave us the results we needed. For most common operations, a single
filter operation is sufficient to get the information we need. However,
filters are of the same class as readers. That is, the general
operations we apply to readers can also be applied to filters. Thus, you
can apply one filter to the data that is generated by another filter.
These readers and filters connected together form what we call a
visualization pipeline. The ability to form visualization pipelines
provides a powerful mechanism for customizing the visualization to your
needs.
Let us play with some more filters. Rather than show the mesh surface in
wireframe, which often interferes with the view of what is inside it, we
will replace it with a cutaway of the surface. We need two filters to
perform this task. The first filter will extract the surface, and the
second filter will cut some away.
(Creating a Visualization Pipeline)
The images and some of the discussion in this exercise assume you are
starting with the state right after finishing Exercise 2.9.
Finish that exercise before beginning this one.
Start by adding a filter that will extract the surfaces. We do that with
the following steps.
Select disk_out_ref.ex2 in the pipeline browser.
From the menu bar, select Filters → Alphabetical
→ Extract Surface. Or bring up the quick launch
(ctrl+space Win/Linux, alt+space Mac), type extract surface, and
select that filter.
Hit the button.
When you apply the Extract Surface filter, you will once again see the
surface of the mesh. Although it looks like the original mesh, it is
different in that this mesh is hollow whereas the original mesh was
solid throughout.
If you were showing the results of the contour filter, you cannot see
the contour anymore, but do not worry. It is still in there hidden by
the surface. If you are showing the contour but you did not see any
effect after applying the filter, you may have forgotten step one and
applied the filter to the wrong object. If the ExtractSurface1 object is
not connected directly to the disk_out_ref.ex2, then this is what went
wrong. If so, you can delete the filter and try again.
Now we will cut away the external surface to expose the internal
structure and isosurface underneath (if you have one).
Verify that ExtractSurface1 is selected in the pipeline browser.
Create a clip filter from the toolbar or Filters menu.
Uncheck the Show Plane checkbox in the properties panel.
Click the button.
If you have a contour, you should now see the isosurface contour within
a cutaway of the mesh surface. You will probably have to rotate the mesh
to see the contour clearly.
Now that we have added several filters to our pipeline, let us take a
look at the layout of these filters in the pipeline browser. The
pipeline browser provides a convenient list of pipeline objects that we
have created. This makes it easy to select pipeline objects and change
their visibility by clicking on the eyeball icons next to them. But
also notice the indentation of the entries in the list and the
connecting lines toward the left. These features reveal the
connectivity of the pipeline. It shows the same information as the
traditional graph layout on the right, but in a much more compact space.
The trouble with the traditional layout of pipeline objects is that it
takes a lot of space, and even moderately sized pipelines require a
significant portion of the GUI to see fully. The pipeline browser,
however, is complete and compact.
Occasionally in the pursuit of science we can narrow our focus down to
one variable. However, most interesting physical phenomena rely on not
one but many variables interacting in certain ways. It can be very
challenging to present many variables in the same view. To help you
explore complicated visualization data, ParaView contains the ability to
present multiple views of data and correlate them together.
So far in our visualization we are looking at two variables: We are
coloring with pressure and have extracted an isosurface with
temperature. Although we are starting to get the feel for the layout of
these variables, it is still difficult to make correlations between
them. To make this correlation easier, we can use multiple views. Each
view can show an independent aspect of the data and together they may
yield a more complete understanding.
On top of each view is a small toolbar, and the buttons controlling the
creation and deletion of views are located on the right side of this
tool bar. There are four buttons in all. You can create a new view by
splitting an existing view horizontally or vertically with the
and buttons, respectively. The button deletes a view, whose
space is consumed by an adjacent view. The temporarily fills view space
with the selected view until is pressed.
(Using Multiple Views)
We are going to start a fresh visualization,
so if you have been following along with the exercises so far, now is
a good time to reset ParaView. The easiest way to do this is to select
Edit → Reset Session from the menu or hit on the
toolbar. This option deletes all of your current work and resets
ParaView back to its initial state. It is roughly the equivalent of
restarting ParaView.
First, we will look at one variable. We need to see the variable through
the middle of the mesh, so we are going to clip the mesh in half.
Open the file disk_out_ref.ex2, load all variables, (see Exercise 2.7).
Add the Clip filter to disk_out_ref.ex2.
Uncheck the Show Plane checkbox in the properties panel.
Click the button.
Color the surface by pressure by changing the variable chooser (in
the toolbar) from vtkBlockColors to pres.
Now we can see the pressure in a plane through the middle of the mesh.
We want to compare that to the temperature on the same plane. To do
that, we create a new view to build another visualization.
Press the button.
The current view is split in half and the right side is blank, ready to
be filled with a new visualization. Notice that the view in the right
has a blue border around it. This means that it is the active view.
Widgets that give information about and controls for a single view,
including the pipeline browser and properties panel, follow the active
view. In this new view we will visualize the temperature of the mesh.
Make sure the blue border is still around the new, blank view (to the
right). You can make any view the active view by simply clicking on
it.
Turn on the visibility of the clipped data by clicking the eyeball
next to Clip1 in the pipeline browser.
Color the surface by temperature by selecting Clip1 in the pipeline
browser and changing the variable chooser (in the toolbar) from Solid
Color to temp.
We now have two views: one showing information about pressure and the
other information about temperature. We would like to compare these, but
it is difficult to do because the orientations are different. How are we
to know how a location in one correlates to a location in the other? We
can solve this problem by adding a camera link so that the two views
will always be drawn from the same viewpoint. Linking cameras is easy.
Right click on one of the views and select Link Camera… from the
pop up menu. (If you are on a Mac with no right mouse button, you can
perform the same operation with the menu option Tools
→ Add Camera Link….)
Click in the second view.
Try moving the camera in each view.
Voilà! The two cameras are linked; each will follow the other. With
the cameras linked, we can make some comparisons between the two views.
Click the button to get a straight-on view of the cross section and
zoom in a bit.
Notice that the temperature is highest at the interface with the heated
disk. That alone is not surprising. We expect the air temperature to be
greatest near the heat source and drop off away from it. But notice that
at the same position the pressure is not maximal. The air pressure is
maximal at a position above the disk. Based on this information we can
draw some interesting hypotheses about the physical phenomenon. We can
expect that there are two forces contributing to air pressure. The first
force is that of gravity causing the upper air to press down on the
lower air. The second force is that of the heated air becoming less
dense and therefore rising. We can see based on the maximal pressure
where these two forces are equal. Such an observation cannot be drawn
without looking at both the temperature and pressure in this way.
Multiview in ParaView is of course not limited to simply two windows.
Note that each of the views has its own set of multiview buttons. You
can create more views by using the split view buttons to arbitrarily divide up the working space. And you can
delete views at any time.
The location of each view is also not fixed. You are also able to swap
two views by clicking on one of the view toolbars (somewhere outside of
where the buttons are), holding down the mouse button, and dragging onto
one of the other view toolbars. This will immediately swap the two
views.
You can also change the size of the views by clicking on the space in
between views, holding down the mouse button, and dragging in the
direction of either one of the views. The divider will follow the mouse
and adjust the size of the views as it moves.
Let us see what else we can learn about this simulation. The simulation
has also outputted a velocity field describing the movement of the air
over the heated rotating disk. We will use ParaView to determine the
currents in the air.
A common and effective way to characterize a vector field is with
streamlines. A streamline is a curve through space that at every
point is tangent to the vector field. It represents the path a
weightless particle will take through the vector field (assuming
steady-state flow). Streamlines are generated by providing a set of
seed points.
(Streamlines)
We are going to start a fresh visualization, so if
you have been following along with the exercises so far, now is a good
time to select reset session from the toolbar.
Open the file disk_out_ref.ex2, load all variables, (see
Exercise 2.7).
Add the stream tracer filter to disk_out_ref.ex2.
Change the Seed Type parameter in the properties panel to Point
Cloud.
Uncheck the Show Sphere checkbox in the properties
panel under the seed type.
Click the button to accept these parameters.
The surface of the mesh is replaced with some swirling lines. These
lines represent the flow through the volume. Notice that there is a
spinning motion around the center line of the cylinder. There is also a
vertical motion in the center and near the edges.
The new geometry is off-center from the previous geometry. We can
quickly center the view on the new geometry with the reset camera
command. This command centers and fits the visible geometry within the
current view and also resets the center of rotation to the middle of the
visible geometry.
One issue with the streamlines as they stand now is that the lines are
difficult to distinguish because there are many close together and they
have no shading. Lines are a 1D structure and shading requires a 2D
surface. Another issue with the streamlines is that we cannot be sure in
which direction the flow is.
In the next exercise, we will modify the streamlines we created in
Exercise 2.12 to correct these problems. We can create a 2D
surface around our stream traces with the tube filter. This surface
adds shading and depth cues to the lines. We can also add glyphs to
the lines that point in the direction of the flow.
(Making Streamlines Fancy)
This exercise is a continuation of Exercise 2.12. You will
need to finish that exercise before beginning this one.
Use the quick launch (ctrl+space Win/Linux, alt+space Mac) to add the
Tube filter to the streamlines.
Hit the button.
You can now see the streamlines much more clearly. As you look at the
streamlines from the side, you should be able to see circular convection
as air heats, rises, cools, and falls. If you rotate the streams to look
down the Z axis at the bottom near where the heated plate should be, you
will also see that the air is moving in a circular pattern due to the
friction of the rotating disk.
(Note that as an alternative to adding the Tube filter, you can instead
directly render lines as tubes. This applies a special rendering mode
that renders wide lines with tube-like shading. To do this, instead of
creating the Tube filter set Line Width display parameter to some value
larger than 1 (say 5) and click on the Render Lines As Tubes display
parameter.)
Now we can get a little fancier. We can add glyphs to the streamlines to
show the orientation and magnitude.
Select StreamTracer1 in the pipeline browser.
Add the glyph filter to StreamTracer1.
In the properties panel, change the Glyph Type option to Cone.
In the properties panel, change the Orientation Array to v.
In the properties panel, change the Scale Array to v.
Click the reset button to the right of Scale Factor.
Hit the button.
Color the glyphs with the temp variable.
Now the streamlines are augmented with little pointers. The pointers
face in the direction of the velocity, and their size is proportional to
the magnitude of the velocity. Try using this new information to answer
the following questions.
Where is the air moving the fastest? Near the disk or away from it?
At the center of the disk or near its edges?
Which way is the plate spinning?
At the surface of the disk, is air moving toward the center or away
from it?
ParaView’s plotting capabilities provide a mechanism to drill down into
your data to allow quantitative analysis. Plots are usually created with
filters, and all of the plotting filters can be found in the Data
Analysis submenu of Filters. There is also a data analysis toolbar
containing the most common data analysis filters, some of which are used
to generate plots.
Compute Quartiles
Computes the quartiles for each field in the data set and then shows
a box chart depicting the quartiles.
Extract Selection
Extracts any data selected into its own object. Selections are
described in Section 2.14.
Histogram
Allows you to generate the histogram of a data array from a dataset.
Plot Global Variables Over Time
Data sets sometimes capture information in “global” variables that
apply to an entire dataset rather than a single point or cell. This
filter plots the global information over time. ParaView’s handling of
time is described in Section 2.11.
Plot Over Line
Allows you to define a line segment in 3D space and then plot field
information over this line.
Plot Selection Over Time
Takes the fields in selected points or cells and plots their values
over time. Selections are described in Section 2.14 and
time is described in Section 2.11.
Probe
Provides the field values in a particular location in space.
Programmable Filter
Allows you to program a user-defined filter. To use the filter you
define a function that retrieves input of the correct type, creates
data, and then manipulates the output of the filter.
In the next exercise, we create a filter that will plot the values of
the mesh’s fields over a line in space.
(Plot Over a Line in Space)
We are going to start a fresh visualization, so if
you have been following along with the exercises so far, now is a good
time to reset ParaView. The easiest way to do this is to select
from the toolbar.
Open the file disk_out_ref.ex2, load all variables, (see
Exercise 2.7).
Add the Clip filter to disk_out_ref.ex2, Uncheck the Show
Plane and the Invert checkboxes in the properties
panel, and click (like in Exercise 2.11). This will
make it easier to see and manipulate the line we are plotting over.
Click on disk_out_ref.ex2 in the pipeline browser to make that the
active object.
From the toolbars, select the plot over line filter.
In the active view you will see a line through your data with a ball at
each end. If you move your mouse over either of these balls, you can
drag the balls through the 3D view to place them. If you hold down the
x, y, or z key while you drag one of these balls, the movement will be
constrained to that axis. Notice that each time you move the balls some
of the fields in the properties panel also change. You can also place
the balls by hovering your mouse over the target location and hitting
the 1, 2, or p key. The 1 key will place the first ball at the surface
underneath the mouse cursor. The 2 key will likewise place the second
ball. The p key will alternate between placing the first and second
balls. If you hold down the Ctrl modifier while hitting any of these
keys, then the ball will be placed at the nearest point of the
underlying mesh rather than directly under the mouse. This was the
purpose of adding the clip filter: It allows us to easily add the
endpoints to this plane. Note that placing the endpoints in this manner
only works when rendering solid surfaces. It will not work with a volume
rendered image or transparent surfaces.
This representation is called a 3D widget because it is a GUI
component that is manipulated in 3D space. There are many examples of 3D
widgets in ParaView. This particular widget, the line widget, allows you
to specify a line segment in space. Other widgets allow you to specify
points or planes.
Adjust the line so that it goes from the base of the disk straight up
to the top of the mesh using the 3D widget manipulators, the p key
shortcut, or the properties panel parameters. The plot works best
with Point 1 around \((0,0,0)\) and Point 2 around
\((0,0,10)\).
Once you have your line satisfactorily located, click the button.
There are several interactions you can do with the plot. Roll the mouse
wheel up and down to zoom in and out. Drag with the middle button to do
a rubber band zoom. Drag with the left button to scroll the plot around.
You can also use the reset camera command to restore the
view to the full domain and range of the plot.
Plots, like 3D renderings, are considered views. Both provide a
representation for your data; they just do it in different ways. Because
plots are views, you interact with them in much the same ways as with a
3D view. If you look in the Display section of the properties panel, you
will see many options on the representation for each line of the plot
including colors, line styles, vector components, and legend names.
If you scroll down further to the View section of the properties panel,
you to change plot-wide options such as labels, legends, and axes
ranges.
Like any other views, you can capture the plot with the File
→ Save Screenshot. Additionally, if you choose File
→ Export Scene… you can export a file with vector
graphics that will scale properly for paper-quality images. We will
discuss these image capture features later in Section 2.13.
You can also resize and swap plots in the GUI like you can other views.
In the next exercise, we modify the display to get more information out
of our plot. Specifically, we use the plot to compare the pressure and
temperature variables.
(Plot Series Display Options)
This exercise is a continuation of Exercise 2.14. You will need to
finish that exercise before beginning this one.
Choose a place in your GUI that you would like the plot to go and try
using the split, delete, resize, and swap view features to move it
there.
Make the plot view active, go to the Display section of the
properties panel, and turn off all variables except temp and pres.
The temp and pres variables have different units. Putting them on the
same scale is not useful. We can still compare them in the same plot by
placing each variable on its own scale. The line plot in ParaView allows
for a different scale on the left and right axis, and you can scale each
variable individually on each axis.
Select the pres variable in the Display options.
Change the Chart Axis to Bottom - Right
From this plot we can verify some of the observations we made in
Section 2.7. We can see that the temperature is
maximal at the plate surface and falls as we move away from the plate,
but the pressure goes up and then back down. In addition, we can observe
that the maximal pressure (and hence the location where the forces on
the air are equalized) is about 3 units away from the disk.
The ParaView framework is designed to accommodate any number of
different types of views. This is to provide researchers and developers
a way to deliver new ways of looking at data. To see another example of
view, select disk_out_ref.ex2 in the pipeline browser, and then select
Filters → Data Analysis → Histogram . Make the histogram
for the temp variable, and then hit the button.
ParaView has several ways to represent data. We have already seen some
examples: surfaces, wireframe, and a combination of both. ParaView can
also render the points on the surface or simply draw a bounding box of
the data.
A powerful way that ParaView lets you represent your data is with a
technique called volume rendering. With volume rendering, a solid
mesh is rendered as a translucent cloud with the scalar field
determining the color and density at every point in the cloud. Unlike
with surface rendering, volume rendering allows you to see features all
the way through a volume.
Volume rendering is enabled by simply changing the representation of the
object. Let us try an example of that now.
(Turning On Volume Rendering)
We are going to start a fresh visualization, so
if you have been following along with the exercises so far, now is a
good time to reset ParaView. The easiest way to do this is to select
from the toolbar.
Open the file disk_out_ref.ex2, load all variables, (see
Exercise 2.7.
Make sure disk_out_ref.ex2 is selected in the pipeline browser.
Change the variable viewed to temp and change the representation to
Volume.
If you get an Are you sure? dialog box warning you about the change
to the volume representation, click Yes to enact the change.
Show Center of rotation.
The solid opaque mesh is replaced with a translucent volume. You may
notice that when rotating your object that the rendering is temporarily
replaced with a simpler transparent surface for performance reasons. We
discuss this behavior in more detail later in Section 4.
A useful feature of ParaView’s volume rendering is that it can be mixed
with the surface rendering of other objects. This allows you to add
context to the volume rendering or to mix visualizations for a more
information-rich view. For example, we can combine this volume rendering
with a streamline vector visualization like we did in Exercise 2.12.
(Combining Volume Rendering and Surface-Based Visualization)
This exercise is a continuation of Exercise 2.16.
You will need to finish that exercise before beginning this one.
Add the stream tracer filter to disk_out_ref.ex2.
Change the Seed Type parameter in the properties panel to Point
Cloud.
Uncheck the Show Sphere checkbox in the properties
panel under the seed type.
Click the button to accept these parameters.
You should now be seeing the streamlines embedded within the volume
rendering. The following additional steps add geometry to make the
streamlines easier to see much like in Exercise 2.13.
They are optional, so you can skip them if you wish.
Use the quick launch (ctrl+space Win/Linux, alt+space Mac) to apply
the Tube filter and hit .
If the streamlines are colored by temp, change that to Solid Color.
Select StreamTracer1 in the pipeline browser.
Add the glyph filter to StreamTracer1.
In the properties panel, change the Glyph Type option to Cone.
In the properties panel, change the Orientation Array to v.
In the properties panel, change the Scale Array to v.
Click the reset button to the right of Scale Factor.
Hit the button.
Color the glyphs with the temp variable.
The streamlines are now shown in context with the temperature throughout
the volume.
By default, ParaView will render the volume with the same colors as used
on the surface with the transparency set to 0 for the low end of the
range and 1 for the high end of the range. ParaView also provides an
easy way to change the transfer function, how scalar values are
mapped to color and transparency. You can access the transfer function
editor by selecting the volume rendered-pipeline object (in this case
disk_out_ref.ex2) and clicking on the edit color map button.
The first time you bring up the color map editor, it should appear at
the right side of the ParaView GUI window. Like most of the panels in
ParaView, this is a dockable window that you can move around the GUI or
pull off and place elsewhere on your desktop. Like the properties panel,
some of the advanced options are hidden to simplify the interface. To
access these hidden features, toggle the button in the upper
right or type a search string.
The two colorful boxes at the top represent the transfer function. The
first box with a function plot with colors underneath represents the
transparency whereas the long box at the bottom represents the
colors. The dots on the transfer functions represent the control
points. The control points are the specific color and opacity you set
at particular scalar values, and the colors and transparency are
interpolated between them. Clicking on a blank spot in either bar will
create a new control point. Clicking on an existing control point will
select it. The selected control point can be dragged throughout the box
to change its scalar value and transparency (if applicable). Double
clicking on a color control point will allow you to change the color.
The selected control point will be deleted when you hit the backspace or
delete key.
Did you know?
For surface rendering, the transparency controls have no effect
unless “Enable opacity mapping for surfaces” is enabled.
Directly below the color and transparency bars is a text entry widget to
numerically specify the Data Value of the selected control point. Below
this are checkbox options to Use log scale when mapping data to colors,
to Enable opacity mapping for surfaces, and to Automatically rescale
transfer functions to fit data. (Note that this last option causes the
data range to be resized under most operations that change data, but not
when the time value changes. See Section 2.11 for more details.)
The following Color Space parameter changes how colors are interpolated.
This parameter has no effect on the color at the control points, but can
drastically affect the colors between the control points. Finally, the
Nan Color allows you to select a color for “invalid” values. A NaN
is a special floating point value used to represent something that is
not a number (such as the result of \(0/0\)).
Setting up a transfer function can be tedious, so you can save it by
clicking the Save to preset button. The Choose preset button brings up
a dialog that allows you to manage and apply the color maps that you
have created as well as many provided by ParaView.
(Modifying Volume Rendering Transfer Functions)
This exercise is a continuation of Exercise 2.17.
You will need to finish that exercise (or minimally Exercise 2.16)
before beginning this one.
Click on disk_out_ref.ex2 in the pipeline browser to make that the
active object.
Click on the edit color map button.
Change the volume rendering to be more representative of heat. Press
Choose preset , select Black-Body Radiation in the
dialog box, and then click Apply followed by Close.
Try adding and changing control points and observe their effect on
the volume rendering. By default as you make changes the render views
update. If this interactive update is too slow, you can turn off this
feature by toggling the button. When automatic updates are off,
transfer function changes are not applied until the
Render Views is clicked.
Notice that not only did the color mapping in the volume rendering
change, but all the color mapping for temp changed including the cone
glyphs if you created them. This ensures consistency between the views
and avoids any confusion from mapping the same variable with different
colors or different ranges.
While looking through the color map presents , you probably
noticed one or more entries with Rainbow as part of the title that
incorporate the colors of the a rainbow into the color map. You may also
recognize this set of colors from other visualizations you have seen in the past.
Rainbow colors are certainly a popular choice. However, we recommend
that you never use rainbow color maps in your visualizations.
The problem with rainbow colors is that they have numerous perceptual
properties that serve to obfuscate the data. Although we will not go
into detail into the many perceptual studies that provide evidence that
rainbow colors are bad for data display, we provide a brief synopsis of
the problems.
The first problem is that the colors do not follow any natural perceived
ordering. Some color groups lead to a natural perception of order (with
relative brightness being the strongest perceptual cue). The hues of the
rainbow, however, have no real ordered meaning in our visual system.
Rather, we have to learn an ordering, which can lead to visual
confusion. Consider the following two example images. In the left image,
the rainbow hues make it difficult to ascertain the relative high and
low values that are more clear in the right image.
The second problem with the perception of rainbow colors is that the
perceptual changes in the colors are not uniform. The colors appear to
change faster in the cyan and yellow regions, which can introduce
artifacts in those regions that do not exist in the data. The colors
appear to change more slowly in the blue, green, and red regions, which
creates larger bands of color that hide artifacts in the data. We can
see this effect in the following two images of a spatial contrast
sensitivity function. The grayscale on the left faithfully reproduces
the function. However, the rainbow colors on the right hides the
variation in low contrast regions and appears less smooth in the
high-contrast regions.
A third problem with the rainbow color map is that it is sensitive to
deficiencies in vision. Roughly 5% of the population cannot distinguish
between the red and green colors. Viewers with color deficiencies cannot
distinguish many colors considered “far apart” in the rainbow color map.
We provide this description of the problems with rainbow colors in the
hopes that you do not use these color maps. Despite the well know
problems with rainbow colors, they remain a popular choice. Relying on
rainbow hues obfuscates data, which circumvents the entire process of
data analysis that ParaView provides. Multiple perceptual studies have
shown that subjects overestimate the effectiveness of rainbow colors.
That is, people think they do better with rainbow colors when in fact
they do worse. Don’t fall into this trap.
Now that we have thoroughly analyzed the disk_out_ref simulation, we
will move to a new simulation to see how ParaView handles time. In this
section we will use a new data set from another simple simulation, this
time with data that changes over time.
(Loading Temporal Data)
We are going to start a fresh visualization, so if you have been
following along with the exercises so far, now is a good time to
reset ParaView. The easiest way to do this is to select
from the toolbar.
Open the file can.ex2.
As before, click the checkbox in the header of the block arrays list
to turn on the loading of all the block arrays and hit the button.
Press the button to orient the camera to the mesh.
Press the play button in the toolbars and watch ParaView
animate the mesh to crush the can with the falling brick.
That is really all there is to dealing with data that is defined over
time. ParaView has an internal concept of time and automatically links
in the time defined by your data. Become familiar with the toolbars that
can be used to control time.
Saving an animation is equally as easy. From the menu, select File
→ Save Animation. ParaView provides dialogs
specifying how you want to save the animation, and then automatically
iterates and saves the animation.
(Temporal Data Pitfall)
The biggest pitfall users run into is that
with mapping a set of colors whose range changes over time. To
demonstrate this, do the following.
If you are not continuing from Exercise 2.19,
open the file can.ex2, load all variables, .
Go to the first time step .
Color by the EQPS variable.
Play through the animation (or skip to the last time step ).
The coloring is not very useful. To quickly fix the problem:
While at the last time step, click the Rescale to Data Range button.
Play the animation again.
The colors are more useful now.
Although this behavior seems like a bug, it is not. It is the
consequence of two unavoidable behaviors. First, when you turn on the
visibility of a scalar field, the range of the field is set to the range
of values in the current time step. Ideally, the range would be set to
the max and min over all time steps in the data.
However, this requires ParaView to load in all of the data on the
initial read, and that is prohibitively slow for large data. Second,
when you animate over time, it is important to hold the color range
fixed even if the range in the data changes. Changing the scale of the
data as an animation plays causes a misrepresentation of the data. It is
far better to let the scalars go out of the original color map’s range
than to imply that they have not. There are several workarounds to this
problem:
If for whatever reason your animation gets stuck on a poor color
range, simply go to a representative time step and hit .
This is what we did in the previous exercise.
Open the settings dialog box accessed in the menu from
Edit → Settings (ParaView → Preferences on the Mac). Under the General
tab, find the option labeled Default Time Step and change it to Go to last
timestep. (If you have trouble finding this option, try typing
timestep into the setting’s search box.) When this is selected,
ParaView will automatically go to the last time step when loading any
data set with time. For many data (such as in can), the field ranges
are more representative at the last time step than at the beginning.
Thus, as long as you color by a field before changing the time, the
color range will be adequate.
Click the Rescale to Custom Data Range toolbar button. This is a
good choice if you cannot find, or do not know, a “representative”
time step or if you already know a good range to use.
If you are willing to wait or have small data, you can use the
Rescale to data range over all timesteps toolbar
button and ParaView will compute this overall temporal range automatically.
Keep in mind that this option will require ParaView to load your entire
data set over all time steps. Although ParaView will not hold more than
one time step in memory at a time, it will take a long time to pull all
that memory off of disk for large data sets.
ParaView has many powerful options for controlling time and animation.
The majority of these are accessed through the animation view. From
the menu, click on View → Animation View.
For now we will examine the controls at the top of the animation view.
(We will examine the use of the tracks in the rest of the animation view
later in Section 2.15.) The animation mode
parameter determines how ParaView will step through time during
playback. There are three modes available.
Sequence
Given a start and end time, break the animation into a specified
number of frames spaced equally apart.
Real Time
ParaView will play back the animation such that it lasts the
specified number of seconds. The actual number of frames created
depends on the update time between frames.
Snap To TimeSteps
ParaView will play back exactly those time steps that are defined by
your data.
Whenever you load a file that contains time, ParaView will automatically
change the animation mode to Snap To TimeSteps. Thus, by default you can
load in your data, hit play , and see each time step as defined
in your data. This is by far the most common use case.
A counter use case can occur when a simulation writes data at variable
time intervals. Perhaps you would like the animation to play back
relative to the simulation time rather than the time index. No problem.
We can switch to one of the other two animation modes. Another use case
is the desire to change the playback rate. Perhaps you would like to
speed up or slow down the animation. The other two animation modes allow
us to do that.
(Slowing Down an Animation with the Animation Mode)
We are going to start a fresh visualization, so if you have been following
along with the exercises so far, now is a good time to reset ParaView.
The easiest way to do this is to select from the toolbar.
Open the file can.ex2, load all variables, (see Exercise 2.19).
Press the button to orient the camera to the mesh.
Press the play button in the toolbars.
During this animation, ParaView is visiting each time step in the
original data file exactly once. Note the speed at which the animation
plays.
If you have not done so yet, make the animation view visible: View
→ Animation View.
Change the animation mode to Real Time. By default the animation is
set up with the time range specified by the data and a duration of 10
seconds.
Play the animation again.
The result looks similar to the previous Snap To TimeSteps animation,
but the animation is now a linear scaling of the simulation time and
will complete in 10 seconds.
Change the Duration to 60 seconds.
Play the animation again.
The animation is clearly playing back more slowly. Unless your computer
is updating slowly, you will also notice that the animation appears
jerkier than before. This is because we have exceeded the temporal
resolution of the data set.
Often showing the jerky time steps from the original data is the desired
behavior; it is showing you exactly what is present in the data.
However, if you wanted to make an animation for a presentation, you may
want a smoother animation.
There is a filter in ParaView designed for this purpose. It is called
the temporal interpolator. This filter will interpolate the
positional and field data in between the time steps defined in the
original data set.
(Temporal Interpolation)
This exercise is a continuation of Exercise 2.21.
You will need to finish that exercise before beginning this one.
Make sure can.ex2 is highlighted in the pipeline browser.
Select Filters → Temporal → Temporal Interpolator or apply the Temporal
Interpolator filter using the quick launch (ctrl+space Win/Linux,
alt+space Mac).
.
Split the view , show the TemporalInterpolator1 in one, show
can.ex2 in the other, and link the cameras.
Play the animation.
You should notice that the output from the temporal interpolator
animates much more smoothly than the original data.
It is worth noting that the temporal interpolator can (and often does)
introduce artifacts in the data. It is because of this that ParaView
will never apply this type of interpolation automatically; you will have
to explicitly add the Temporal Interpolator. In general, mesh
deformations often interpolate well but moving fields through a static
mesh do not. Also be aware that the Temporal Interpolator only works if
the topology remains consistent. If you have an adaptive mesh that
changes from one time step to the next, the Temporal Interpolator will
give errors.
When using ParaView as a communication tool it is often helpful to
annotate the images you create with text. With ParaView it is very easy
to create text annotation wherever you want in a 3D view. There is a
special text source that simply places some text in the view.
(: Adding Text Annotation)
If you are continuing this exercise after finishing Exercise 2.22,
feel free to simply continue. If you have had to restart ParaView
since or your state does not match up well enough, it is also fine to
start with a fresh state using .
Use the quick launch (ctrl+space Win/Linux, alt+space Mac) to create
the Text source (or from the menu bar Sources
→ Annotation → Text) and hit .
In the text edit box of the properties panel, type a message.
Hit the button.
The text you entered appears in the 3D view. If you scroll down to the
Display options in the properties panel, you will see six buttons that
allow you to quickly place the text in each of the four corners of the
view as well as centered at the top and bottom.
You can place this text at an arbitrary position by clicking the Lower
Left Corner checkbox. With the Lower Left Corner option checked, you can
use the mouse to drag the text to any position within the view.
Often times you will need to put the current time value into the text
annotation. Typing the correct time value can be tedious and error prone
with the standard text source and impossible when making an animation.
Therefore, there is a special annotate time source that will insert
the current animation time into the string.
(Adding Time Annotation)
If you do not already have it loaded from a previous exercise, open
the file can.ex2, .
Add an Annotate Time source (Sources → Annotate
→ Annotate Time or use the quick launch: ctrl+space
Win/Linux, alt+space Mac). .
Move the annotation around as necessary.
Play and observe how the time annotation changes.
There are instances when the current animation time is not the same as
the time step read from a data file. Often it is important to know what
the time stored in the data file is, and there is a special version of
annotate time that acts as a filter.
Select can.ex2 in the pipeline browser.
Use the quick launch (ctrl+space Win/Linux, alt+space Mac) to apply
the Annotate Time Filter.
.
Move the annotation around as necessary.
Check the animation mode in the Animation View. If it is set to Snap
to TimeSteps, change it to Real Time.
Play and observe how the time annotation changes.
You can close the animation view. We are done with it for now, but we
will revisit it again in Section 2.15.
One of the most important products of any visualization is screenshots
and movies that can be used in presentations and reports. In this
section we save a screenshot (picture) and animation (movie). Once
again, we will use the can.ex2 dataset.
(Save Screenshot)
We are going to start a fresh visualization, so if
you have been following along with the exercises so far, now is a good
time to reset ParaView. The easiest way to do this is to select
from the toolbar.
Open the file can.ex2, load all variables, (see
Exercise 2.19).
Press the button to orient the camera to the mesh.
Color by points’ ids. We use points’ ids so that the 3D object has
some color.
Select File → Save Screenshot .
This brings us to the file selection screen. If you pull down the menu
Files of type: at the bottom of the dialog box, you will see several
file types supported including portable network graphics (PNG), and
joint photographic experts group (JPEG).
Select a File name for your file, and place it somewhere you can later
find and delete. We usually recommend saving images as PNG files. The
lossy compression of JPEG often creates noticeable artifacts in the
images generated by ParaView, and the compression of PNG is better than
most other raster formats.
Press the OK button.
After you select a file, you will be presented with a dialog box for
more screenshot options.
The Save Screenshot Options dialog box includes numerous important
controls.
At the top of the dialog box are Size and Scaling options. The Image
Resolution options allow you to create an image that is larger (or
smaller) than the current size of the 3D view. You can directly enter a
resolution or use the x2 and /2 buttons to double or halve the
resolution. The button toggles locking the aspect ratio when selecting
an image resolution. The button restores the resolution to that of the
view in the GUI. If you have multiple views open, there is also a Save
All Views checkbox that toggles between saving only the active view and
saving all views in one image.
The Coloring controls modify how some elements, such as the background,
get colored. The Override Color Palette pulldown menu allows a user to
use the default color scheme, one with a white color motif for printing,
or other defined palettes. These are the same palettes described in
Exercise [ex:ChangingTheColorPalette]
on page . There is also a Transparent Background checkbox that adds an
alpha channel to the written image (in formats that support it).
There are also many advanced options that, as always are accessible via
the button or the search bar.
Press the OK button.
Using your favorite image viewer, find and load the image you created.
If you have no image viewer, ParaView itself is capable of loading PNG
files.
Next, we will save an animation.
(Save Animation)
If you do not already have it loaded from the previous exercise, open
the file can.ex2, load all variables, and (see Exercise 2.19).
Select File → Save Animation .
This brings us to the file selection screen. If you pull down the menu
Files of type: at the bottom of the dialog box, you will see the several
file types including Ogg/Theora, AVI, JPEG, and PNG.
Select a File name for your file, and place it somewhere you can later
find and delete. AVI will create a movie format that can be used on
windows, and with some open source viewers. Ogg/Theora is used in many
open source viewers. Otherwise, you can create a flipbook, or series
of images. These images can be stitched together to form a movie using
numerous open source tools. For now, try creating an AVI.
Press the OK button.
The Save Animation Options dialog box looks essentially the same as the
Save Screenshot Options dialog for screenshots. If you look at the
advanced options , you may note that there are some added
Animation Options that allow you to control the frame rate and narrow
the time steps that will be animated.
Press the OK button.
Using your favorite movie viewer, find and load the image you created.
The goal of visualization is often to find the important details within
a large body of information. ParaView’s selection abstraction is an
important simplification of this process. Selection is the act of
identifying a subset of some dataset. There are a variety of ways that
this selection can be made, most of which are intuitive to end users,
and a variety of ways to display and process the specific qualities of
the subset once it is identified.
More specifically the subset identifies particular select points, cells,
or blocks within any single data set. There are multiple ways of
specifying which elements to include in the selection including indentifier lists
of multiple varieties, spatial locations, and scalar values and scalar
ranges.
In ParaView, selection can take place at any time, and the program
maintains a current selected set that is linked between all views. That
is, if you select something in one view, that selection is also shown in
all other views that display the same object.
The most direct means to create a selection is via the Find Data
panel. Launch this dialog from the toolbar or the Edit menu. From this
dialog you can enter characteristics of the data that you are searching
for. For example, you could look for points whose velocity magnitude is
near terminal velocity. Or you could look for cells whose strain exceeds
the failure of the material. The following exercise provides a quick
example of using the Find Data panel box.
(Performing Query-Based Selections)
In this exercise we will find all cells with a large equivalent plastic strain (EQPS).
We are going to start a fresh visualization, so if you have been
following along with the exercises so far, now is a good time to reset
ParaView. The easiest way to do this is to select from the toolbar.
Open the file can.ex2, load all variables, (see Exercise 2.19).
Go to the last time step .
Open the find data panel .
From the Data Producer combo box, choose can.ex2.
From the Element Type combo box, choose Cell.
In the third row of widgets, choose EQPS from the first combo box,
is \(>=\) from the second combo box, and enter 1.5 in the final
text box.
Click the Find Data button.
Observe the spreadsheet below the Find Data button that gets populated
with the results of your query. Each row represents a cell and each
column represents a field value or property (such as an identifier).
You may also notice that several cells are highlighted in the 3D view of
the main ParaView window. These highlights represent the selection that
your query created. Close the Find Data panel and note that the
selection remains.
Another way of creating a selection is to pick elements right inside the
3D view. Most of the 3D view selections are performed with a
rubber-band selection. That is, by clicking and dragging the mouse
in the 3D view, you will create a boxed region that will select elements
underneath it. There are also some 3D view selections that allow you to
select within a polygonal region drawn on the screen. There are several
types of interactive selections that can be performed, and you initiate
one by selecting one of the icons in the small toolbar over the 3D view
or using one of the shortcut keys. The following 3D selections are
possible.
Select Cells On (Surface)
Selects cells that are visible in the view under a rubber band.
(Shortcut: s)
Select Points On (Surface)
Selects points that are visible in the view under a rubber band.
(Shortcut: d)
Select Cells Through (Frustum)
Selects all cells that exist under a rubber band. (Shortcut: f)
Select Points Through (Frustum)
Selects all points that exist under a rubber band. (Shortcut: g)
Select Cells With Polygon
Like Select Cells On except that you draw a polygon by dragging the
mouse rather than making a rubber-band selection.
Select Points With Polygon
Like Select Points On except that you draw a polygon by dragging the
mouse rather than making a rubber-band selection.
Select Blocks
Selects blocks in a multiblock data set. (Shortcut: b)
Interactively Select Cells
Enter an interactive selection mode where cells are highlighted as
the mouse hovers over them and selected when clicked.
Interactively Select Points
Enter an interactive selection mode where points are highlighted as
the mouse hovers near them and selected when clicked.
In addition to these selection modes, there are a hover point query mode
and a hover cell query mode that allow you to quickly inspect the field
values at a visible point by hovering the mouse over it. There is also a
clear selection button that will remove the current selection.
Several of the selection modes have shortcut keys that allow you to make
selections more quickly. Use them by placing the mouse cursor somewhere
in the currently selected 3D view and hitting the appropriate key. Then
click on the cell or block you want selected (or drag a rubber band over
multiple elements).
Feel free to experiment with the selections now.
You can manage your selection with the Find Data panel even if the
selection was created with one of these 3D interactions rather than
directly with a find data query. The find data panel allows you to view
all the points and cells in the selection as well as perform simple
operations on the selection. These include inverting the selection (a
checkbox just over the spreadsheet), adding labels (Exercise 2.29),
freezing selections (Exercise 2.28),
and shortcuts for the Plot Selection Over Time and
Extract Selection filters (Exercise 2.30 and
Exercise 2.31, respectively).
Experiment with selections in Find Data a bit. Open the Find Data
panel. Then make selections using the rubber-band selection and see
the results in the Find Data panel. Also experiment with altering
the selection by inverting selections with the Invert selection
checkbox.
It should be noted that selections can be internally represented in
different ways. Some are recorded as a list of data element ids. Others
are specified as a region in space or by query parameters. Although the
selections all look the same, they can behave differently, especially
with respect to changes in time. The following exercise demonstrates how
these different selection mechanisms can behave differently.
(Data Element Selections vs. Spatial Selections)
If you do not already have it loaded from the previous exercise, open
the file can.ex2, load all variables, (see Exercise 2.19).
Make a selection using the Select Cells Through tool.
If it is not already visible, show the Find Data panel.
Play the animation a bit. Notice that the region remains fixed and
the selection changes based on what cells move in or out of the
region.
Go to a timestep where some data are selected. In the Find Data
panel, click the Freeze Selection button.
Play again. Notice that the cells selected are fixed regardless of
position.
In summary, a spatial selection (created with one of the select through
tools) will re-perform the selection at each time step as elements move
in and out of the selected region. Likewise, other queries such as field
range queries will also re-execute as the data changes. However, when
you select the Freeze Selection button, ParaView captures the
identifiers of the currently selected elements so that they will remain
the same throughout the animation.
The spreadsheet in the find panel provides a readable way to inspect
field data. However, sometimes it is helpful to place the field data
directly in the 3D view. The next exercise describes how we can do that.
(Labeling Selections)
If you do not already have it loaded from the previous exercise, open
the file can.ex2, load all variables, (see Exercise 2.19).
Go to the last time step .
If it is not already visible, show the Find Data panel.
Using the controls at the top of the find data panel, create a
selection where cells’ ids is min. Click Find Data.
In the Cell Labels chooser, select EQPS.
ParaView places the values for the EQPS field near the selected cell
that contains that value. You should be able to see it in the 3D view.
It is also possible to change the look of the font with respect to type,
size, and color by clicking the button to the right of the
label choosers.
When you are done, turn off the labels by unchecking the entry in the
Cell Labels chooser.
ParaView provides the ability to plot field data over time. These plots
can work on a selection, and to make this easier the Find Data panel
contains convenience controls to create them.
(Plot Over Time)
If you do not already have it loaded from the previous exercise, open
the file can.ex2, load all variables, (see Exercise 2.19).
If it is not already visible, show the Find Data panel.
Using the controls at the top of the find data panel, create a
selection where EQPS is max. Click Find Data.
Click the Plot Selection Over Time button at the bottom of the find
data panel to add that filter. This filter is also easily
accessible by the toolbar button in the main ParaView window.
In the properties panel in the main ParaView window, click .
Note that the selection you had was automatically added as the selection
to use in the Properties panel when the Plot Selection Over Time
filter was created. If you want to change the selection, simply make a new one
and click Copy Active Selection in the Properties panel.
Also note that the plot was for the maximum EQPS value at each timestep,
which could potentially be from a different cell at every timestep. If
the desire is to identify a cell with a maximum value at some timestep
and then plot that cell’s value at every timestep, then use the Freeze
Selection feature demonstrated in Exercise 2.28.
You can also extract a selection in order to view the selected points or
cells separately or perform some independent processing on them. This is
done through the Extract Selection filter.
(Extracting a Selection)
We are going to start a fresh visualization,
so if you have been following along with the exercises so far, now is
a good time to reset ParaView. The easiest way to do this is to select
from the toolbar.
Open the file can.ex2, load all variables, (see
Exercise 2.19).
Make a sizable cell selection for example, with Select Cells Through
.
Create an Extract Selection filter (available on the
toolbar and from the find data panel).
.
The object in the view is replaced with the cells that you just
selected. (Note that in this image I added a translucent surface and a
second view with the original selection to show the extracted cells in
relation to the full data.) You can perform computations on the
extracted cells by simply adding filters to the extract selection
pipeline object.
As we described before, Views and Find Data panel can be used to create
different types of selections. To save and combine the created selections, you can use
the SelectionEditor panel. This panel can be accessed from View → Selection Editor.
(Selection Editor)
We are going to start a fresh visualization,
so if you have been following along with the exercises so far, now is
a good time to reset ParaView. The easiest way to do this is to select
from the toolbar.
Open the file can.ex2, load all variables, (see
Exercise 2.19) and click .
Enable View → Selection Editor.
Use to create a frustum cell selection at the bottom-left part of the can,
and press in the Selection Editor to save the created selection. As you can see the
saved selection has a name s0, and it’s described as a frustum selection.
Use to select the top block of the can and press in the Selection Editor
to save the created selection.
On top of the frustum selection that you created previously, use to create a
slightly smaller polygon cell selection, and press in the Selection Editor to save the
created selection.
You can click on the previous Frustum selection in the Selection Editor to interactively visualize it.
Open the Find data panel , select can.ex2 as the Data Producer, select Cell as the Element
Type, and set ID \(>=\) 3600, press in the Find data panel and set ID \(>=\) 3900. Finally,
press in the Selection Editor to save the created selection.
The Selection Editor should now have 4 different selections, which can be combined using a boolean
expression. Set Expression to \(s1|(s0\) ^ \(s2)|s3\).
Press Activate Combined Selections.
More information regarding the Selection Editor can be found in
Section 6.8 of the User’s Guide.
We have already seen how to animate a data set with time in it (hit )
and other ways to manipulate temporal data in Section 2.11. However,
ParaView’s animation capabilities go far beyond that. With ParaView you
can animate nearly any property of any pipeline object.
(Animating Properties)
We are going to start a fresh visualization, so if you have been following
along with the exercises so far, now is a good time to reset ParaView.
The easiest way to do this is to select from the toolbar.
Use the quick launch (ctrl+space Win/Linux, alt+space Mac) to create
the Sphere source and it.
If the animation view is not visible, make it so: View → Animation View.
Change the No. Frames option to 50 (10 will go far too quickly).
Find the property selection widgets at the bottom of the animation
view and select Sphere1 in the first box and Start Theta in the
second box.
Hit the button.
If you play the animation, you will see the sphere open up
then eventually wrap around itself and disappear.
What you have done is created a track for the Start Theta property
of the Sphere1 object. A track is represented as horizontal bars in the
animation view. They hold key frames that specify values for the
property at a specific time instance. The value for the property is
interpolated between the key frames. When you created a track two key
frames were created automatically: a key frame at the start time with
the minimal value and a key frame at the end time with the maximal
value. The property you set here defines the start range of the sphere.
You can modify a track by double clicking on it. That will bring up a
dialog box that you can use to add, delete, and modify key frames.
We use this feature to create a new key frame in the animation in the
next exercise.
(Modifying Animation Track Keyframes)
This exercise is a continuation of Exercise 2.33.
You will need to finish that exercise before beginning this one.
Double-click on the Sphere1 – Start Theta track.
In the Animation Keyframes dialog, click the New button. This will
create a new key frame.
Modify the first key frame value to be 360.
Modify the second key frame time to be 0.5 and value to be 0.
Click OK.
When you play the animation, the sphere will first get bigger and then
get smaller again.
You are not limited to animating just one property. You can animate any
number of properties you wish. Now we will create an animation that
depends on modifying two properties.
(Multiple Animation Tracks)
This exercise is a continuation of Exercise 2.33
and Exercise 2.34.
You will need to finish those exercises before beginning this one.
Double-click on the Sphere1 – Start Theta track.
In the Animation Keyframes dialog, Delete the first track (at time
step 0).
Click OK.
In the animation view, create a track for the Sphere1 object, End
Theta property.
Double-click on the Sphere1 – End Theta track.
Change the time for the second key frame to be 0.5.
The animation will show the sphere creating and destroying itself, but
this time the range front rotates in the same direction. It makes for a
very satisfying animation when you loop the animation.
In addition to animating properties for pipeline objects, you can
animate the camera. ParaView provides methods for animating the camera
along curves that you specify. The most common animation is to rotate
the camera around an object, always facing the object, and ParaView
provides a means to automatically generate such an animation.
(Camera Orbit Animations)
For this exercise, we will orbit the camera
around whatever data you have loaded. If you are continuing from the
previous exercise, you are set up. If not, simply load or create some
data. To see the effects, it is best to have asymmetry in the geometry
you load. can.ex2 is a good data set to load for this exercise.
Place the camera where you want the orbit to start. The camera will
move to the right around the viewpoint.
Make sure the animation view panel is visible (View → Animation View
if it is not).
In the property selection widgets, select Camera in the first box and
Orbit in the second box.
Hit the button.
Before the new track is created, you will be presented with a dialog box
that specifies the parameters of the orbit. The default values come from
the current camera position, which is usually what you want.
Click OK.
Play .
The camera will now animate around the object.
Another common camera annotation is to follow an object as it moves
through space. Imagine a simulation of a traveling bullet or vehicle. If
we hold the camera steady, then the object will quickly move out of
view. To help with this situation, ParaView provides a special track
that allows the camera to follow the data in the scene.
(Following Data in an Animation)
We are going to start a fresh visualization, so if you have been following
along with the exercises so far, now is a good time to reset ParaView.
The easiest way to do this is to select from the toolbar.
Open the file can.ex2, load all variables, (see Exercise 2.19).
Press the button to orient the camera to the mesh.
Make sure the animation view panel is visible (View
→ Animation View if it is not).
In the property selection widgets, select Camera in the first box and
Follow Data in the second box.
Hit the button.
Play .
Note that instead of the can crushing to the bottom of the view, the
animation shows the can lifted up to be continually centered in the
image. This is because the camera is following the can down as it is
crushed.
Python scripting can be leveraged in two ways within ParaView. First,
Python scripts can automate the setup and execution of visualizations by
performing the same actions as a user at the GUI. Second, Python scripts
can be run inside pipeline objects, thereby performing parallel
visualization algorithms. This chapter describes the first mode, batch
scripting for automating the visualization.
Batch scripting is a good way to automate mundane or repetitive tasks,
but it is also a critical component when using ParaView in situations
where the GUI is undesired or unavailable. The automation of Python
scripts allows you to leverage ParaView as a scalable parallel
post-processing framework. We are also leveraging Python scripting to
establish in situ computation within simulation code. (ParaView
supports an in situ library called Catalyst, which is documented
in Section 4.10 of this tutorial and
more fully online at https://www.paraview.org/in-situ/).
This tutorial gives only a brief introduction to Python scripting. More
comprehensive documentation on scripting is given in the ParaView
User’s Guide. There are also further links on ParaView’s documentation
web page (https://www.paraview.org/documentation) including a complete
reference to the ParaView Python API.
There are many ways to invoke the Python interpreter. The method you use
depends on how you are using the scripting. The easiest way to get a
python interpreter, and the method we use in this tutorial, is to select
View → Python Shell from the menu. This will bring up
a dialog box containing controls for ParaView’s Python shell. This is
the Python interpreter, where you directly control ParaView via the
commands described later. For convenience in typing, ParaView’s Python
shell supports tab completion and history browsing with the up and down
keys.
If you are most interested in getting started on writing scripts, feel
free to skip to the next section past the discussion of the other ways
to invoke scripting.
ParaView comes with two command line programs that execute Python
scripts: pvpython and pvbatch. They are similar to the
python executable that comes with Python distributions in that they
accept Python scripts either from the command line or from a file and
they feed the scripts to the Python interpreter.
The difference between pvpython and pvbatch is subtle and has to
do with the way they establish the visualization service. pvpython
is roughly equivalent to the paraview client GUI with the GUI
replaced with the Python interpreter. It is a serial application that
connects to a ParaView server (which can be either builtin or remote).
pvbatch is roughly equivalent to pvserver except that commands
are taken from a Python script rather than from a socket connection to a
ParaView client. It is a parallel application that can be launched with
mpirun (assuming it was compiled with MPI), but it cannot connect to
another server; it is its own server. In general, you should use
pvpython if you will be using the interpreter interactively and
pvbatch if you are running in parallel.
It is also possible to use the ParaView Python modules from programs
outside of ParaView. This can be done by pointing the PYTHONPATH
environment variable to the location of the ParaView libraries and
Python modules and pointing the LD_LIBRARY_PATH (on Unix/Linux),
DYLD_LIBRARY_PATH (on Mac), or PATH (on Windows) environment
variable to the ParaView libraries. Running the Python script this way
allows you to take advantage of third-party applications such as
Python’s Integrated Development and Learning Environment (IDLE).
For more information on setting up your environment, consult the
ParaView Wiki.
Before diving into the depths of the Python scripting features, let us
take a moment to explore the automated facilities for creating Python
scripts. The ParaView GUI’s Python Trace feature allows one to very
easily create Python scripts for many common tasks. To use Trace, one
simply begins a trace recording via Start Trace, found in the Tools
menu, and ends a trace recording via Stop Trace, also found in the Tools
menu. This produces a Python script that reconstructs the actions taken
in the GUI. That script contains the same set of operations that we are
about to describe. As such, Trace recordings are a good resource when
you are trying to figure out how to do some action via the Python
interface, and conversely the following descriptions will help in
understanding the contents of any given Trace script.
(Creating a Python Script Trace)
If you have been following an exercise in a previous section, now
is a good time to reset ParaView. The easiest way to do this is
to select Edit → Reset Session from the menu or hit on the toolbar.
Click the Start Trace option in the Tools menu.
A dialog box with options for the trace is presented. We will discuss
the meaning of these options later. For now, just click OK.
Build a simple pipeline in the main ParaView GUI. For example, create
a sphere source and then clip it.
Click Stop Trace in the Tools menu.
An editing window will open populated with a Python script that
replicates the operations you just made.
Even if you have not been exposed to ParaView’s Python bindings, the
commands being performed in the traced script should be familiar. Once
saved to your hard drive, you can of course edit the script with your
favorite editor. The final script can be interpreted by the pvpython
or pvbatch program for totally automated visualization. It is also
possible to run this script in the GUI. The Python Shell dialog has a
Run Script button that invokes a saved script.
It should be noted that there is also a way to capture the current
ParaView state as a Python script without tracing actions. Simply select
Save State… from the ParaView File menu and choose to save as a Python
.py state file (as opposed to a ParaView .pvsm state file). We will not
have an exercise on state Python scripts, but suffice it to say they can
be used in much the same way as traced Python scripts. You are welcome
to experiment with this feature as you like.
As noted earlier in the exercise, Python tracing has some options that
are presented in a dialog box before the tracing starts. The first
option selections what properties are saved to the trace. Some
properties you explicitly set through the GUI, such as a value entered
in a GUI widget. Some properties are set internally by the ParaView
application, such as the initial position of a clip plane based on the
bounds of the object it is being applied to. Many other properties are
left at some default value. You can choose one of the following classes
of properties to save:
all properties
Traces the values of all properties even if they remain at the
default. This can be helpful to introspect all possible properties or
to ensure a consistent state regardless of the settings for other
users. This also yields a very verbose output that can be hard to
read.
any *modified* properties
Ignores any properties that do not change from their defaults. This
is a good option for most use cases.
only *user-modified* properties
Ignores any properties that are not explicitly set by the user.
Traces of this nature rely on any internally set properties being
reapplied when the script is run.
The next option has to do with supplemental objects that are managed by
the ParaView GUI (or client) rather than in the server’s state. Check
this box to capture all of the state associated with these objects,
which includes color maps, color bars, and other annotation.
Finally, ParaView provides the option to show the trace file as it is
being generated. This can be a helpful option to use when learning what
Python commands can be used to replicate particular actions in the
ParaView GUI.
A simple but powerful way to customize the behavior of ParaView is to
add your Python script as a macro. A macro is simply an automated
script that can be invoked through its button in a toolbar or its entry
in the menu bar. Any Python script can be assigned to a macro.
(Adding a Macro)
This exercise is a continuation of Exercise 3.1.
You will need to finish that exercise before beginning this one. You
should have the editing window containing the Python script created in
Exercise 3.1 open.
In the menu bar (of the editing window), select File → Save As Macro….
Choose a descriptive name for the macro file and save it in the
default directory provided by the browser. You should now see your
macro on the Macro toolbar at the top of the ParaView GUI.
At this point, you should now see your macro added to the toolbars. By
default, macro toolbar buttons are placed in the middle row all the way
to the right. If you are short on space in your GUI, you may need to
move toolbars around to see it. You will also see that your macro has
been added to the Macros menu.
Close the Python editor window.
Delete the pipeline you have created by either selecting Edit
→ Delete All from the menu or selecting from the
toolbar.
Activate your macro by clicking on the toolbar button or selecting it
in the Macros menu.
In this example our macro created something from scratch. This is
helpful if you often load some data in the same way every time. You can
also trace the creation of filters that are applied to existing data. A
macro from a trace of this nature allows you to automate the same
visualization on different data.
As described in the previous two sections, the ParaView GUI’s Python
Trace feature provides a simple mechanism to create scripts. In this
section we will begin to describe the basic bindings for ParaView
scripting. This is important information in building Python scripts, but
you can always fall back on producing traces with the GUI.
The first thing any ParaView Python script must do is load the
paraview.simple module. This is done by invoking
fromparaview.simpleimport*
In general, this command needs to be invoked at the beginning of any
ParaView batch Python script. This command is automatically invoked for
you when you bring up the scripting dialog in ParaView, but you must add
it yourself when using the Python interpreter in other programs
(including pvpython and pvbatch).
The paraview.simple module defines a function for every source,
reader, filter, and writer defined in ParaView. The function will be the
same name as shown in the GUI menus with spaces and special characters
removed. For example, the Sphere function corresponds to Sources
→ Sphere in the GUI and the PlotOverLine function
corresponds to Filters → Data Analysis
→ Plot Over Line. Each function creates a pipeline
object, which will show up in the pipeline browser (with the exception
of writers), and returns an object that is a proxy that can be used
to query and manipulate the properties of that pipeline object.
There are also several other functions in the paraview.simple module
that perform other manipulations. For example, the pair of functions
Show and Hide turn on and off, respectively, the visibility of a
pipeline object in a view. The Render function causes a view to be
redrawn.
To obtain a concise list of the functions available in
paraview.simple, invoke dir(paraview.simple). Alternatively, as
explained in Section 3.6 you can get a verbose
listing via help(paraview.simple).
(Creating and Showing a Source)
If you have been following an exercise
in a previous section, now is a good time to reset ParaView. The
easiest way to do this is to select from the toolbar.
If you have not already done so, open the Python shell in the ParaView
GUI by selecting View → Python Shell from the menu.
You will notice that the following has been added for you already.
fromparaview.simpleimport*
Create and show a Sphere source by typing the following in the Python
shell.
sphere=Sphere()Show()Render()ResetCamera()
The Sphere command creates a sphere pipeline object. Once it is
executed you will see an item in the pipeline browser created. We save a
proxy to the pipeline object in the variable sphere. We are not
using this variable (yet), but it is good practice to save references to
your pipeline objects.
The subsequent Show command turns on visibility of this object in
the view, and the subsequent Render causes the results to be seen.
Finally, although the ParaView GUI automatically adjusts the camera to
data shown for the first time, the Python scripting does not. The call
to ResetCamera performs this automatic camera adjustment if
necessary.
At this point you can interact directly with the GUI again. Try changing
the camera angle in the view with the mouse.
(Creating and Showing a Filter)
Creating filters is almost identical to creating sources. By default,
the last created pipeline object will be set as the input to the newly
created filter, much like when creating filters in the GUI.
This exercise is a continuation of Exercise 3.3.
You will need to finish that exercise before beginning this one.
Type in the following script in the Python shell that hides the sphere
and then adds the shrink filter to the sphere and shows that.
Hide()shrink=Shrink()Show()Render()
The sphere should be replaced with the output of the Shrink filter,
which makes all of the polygons smaller to give the mesh an exploded
type of appearance.
So far as we have built pipelines, we have accepted the default
parameters for the pipeline objects. As we have seen in the exercises of
Section 2, it is common to have
to modify the parameters of the objects using the properties panel.
In Python scripting, we use the proxy returned from the creation
functions to manipulate the pipeline objects. These proxies are in fact
Python objects with class attributes that correspond to the same
properties you set in the properties panel. They have the same names as
those in the properties panel with spaces and other illegal characters
removed. Use dir(variable) or help(variable) to get a list of
all attributes on any variable that you have access to. In most cases,
simply assign values to an object’s attributes in order to change them.
(Changing Pipeline Object Properties)
This exercise is a continuation of Exercise 3.3 and
Exercise 3.4. You will need to finish those exercises
before beginning this one.
Recall that we have so far created two Python variables, sphere and
shrink, that are proxies to the corresponding pipeline objects.
First, enter the following command into the Python shell to get a
concise listing of all attributes of the sphere.
dir(sphere)
Next, enter the following command into the Python shell to get the
current value of the Theta Resolution property of the sphere.
print(sphere.ThetaResolution)
The Python interpreter should respond with the result 8. (Note that
using the print function, which instructs Python to output the
arguments to standard out, is superfluous here as the Python shell will
output the result of any command anyway.) Let us double the number of
polygons around the equator of the sphere by changing this property.
sphere.ThetaResolution=16Render()
The shrink filter has only one property, Shrink Factor. We can adjust
this factor to make the size of the polygons larger or smaller. Let us
change the factor to make the polygons smaller.
shrink.ShrinkFactor=0.25Render()
You may have noticed that as you type in Python commands to change the
pipeline object properties, the GUI in the properties panel updates
accordingly.
So far we have created only non-branching pipelines. This is a simple
and common case and, like many other things in the paraview.simple
module, is designed to minimize the amount of work for the simple and
common case but also provide a clear path to the more complicated cases.
As we have built the non-branching pipeline, ParaView has automatically
connected the filter input to the previously created object so that the
script reads like the sequence of operations it is. However, if the
pipeline has branching, we need to be more specific about the filter
inputs.
Recall that we have so far created two Python variables, sphere and
shrink, that are proxies to the corresponding pipeline objects. We
will now add a second filter to the sphere source that will extract the
wireframe from it. Enter the following in the Python shell.
An Extract Edges filter is added to the sphere source. You should now
see both the wireframe of the original sphere and the shrunken polygons.
Notice that we explicitly set the input for the Extract Edges filter by
providing Input=sphere as an argument to the ExtractEdges
function. What we are really doing is setting the Input property
upon construction of the object. Although it would be possible to create
the object with the default input, and then set the input later, it is
not recommended. The problem is that not all filters accept all input.
If you initially create a filter with the wrong input, you could get
error messages before you get a chance to change the Input property
to the correct input.
The sphere source having two filters connected to its output is an
example of fan out in the pipeline. It is always possible to have
multiple filters attached to a single output. Some filters, but not all,
also support having multiple filters connected to their input. Multiple
filters are attached to an input is known as fan in. In ParaView’s
Python scripting, fan in is handled much like fan out, by explicitly
defining a filter’s inputs. When setting multiple inputs (on a single
port), simply set the input to a list of pipeline objects rather
than a single one.
Did you know?
Filters that have multiple input ports, like ResampleWithDataset,
use different names to distinguish amongst the input properties
instead. The ports are typically called Input and Source but
consult Trace or help to be sure.
For example, let us group the results of the shrink and extract edges filters
using the Group Datasets filter. Type the following line in the Python shell.
There is now no longer any reason for showing the shrink and extract
edges filters, so let us hide them. By default, the Show and
Hide functions operate on the last pipeline object created (much
like the default input when creating a filter), but you can explicitly
choose the object by giving it as an argument. To hide the shrink and
extract edges filters, type the following in the Python shell.
Hide(shrink)Hide(wireframe)Render()
In the previous exercise, we saw that we could set the Input
property by placing Input=({inputobject}) in the
arguments of the creator function. In general we can set any of the
properties at object construction by specifying
{propertyname}={propertyvalue}. For example, we can set both the
ThetaResolution and PhiResolution when we
create a sphere with a line like this.
If you have any experience with the ParaView GUI, then you should
already be familiar with the concept of an active object. As you build
and manipulate visualizations within the GUI, you first have to select
an object in the pipeline browser. Other GUI panels such as the
properties panel will change based on what the active object is. The
active object is also used as the default object to use for some
operations such as adding a filter.
The batch Python scripting also understands the concept of the active
object. In fact, when running together, the GUI and the Python
interpreter share the same active object. When you created filters in
the previous section, the default input they were given was actually the
active object. When you created a new pipeline object, that new object
became the active one (just like when you create an object in the GUI).
You can get and set the active object with the GetActiveSource and
SetActiveSource functions, respectively. You can also get a list of
all pipeline objects with the GetSources function. When you click on
a new object in the GUI pipeline browser, the active object in Python
will change. Likewise, if you call SetActiveSource in python, you
will see the corresponding entry become highlighted in the pipeline
browser.
(Experiment with Active Pipeline Objects)
This exercise is a continuation of the exercises in the previous section.
However, if you prefer you can create any pipeline you want and follow along.
Play with active objects by trying the following.
Get a list of objects by calling GetSources(). Find the sources
and filters you created in that list.
Get the active object by calling GetActiveSource(). Compare that
to what is selected in the pipeline browser.
Select something new in the pipeline browser and call
GetActiveSource() again.
Change the active object with the SetActiveSource() function. You
can use one of the proxy objects you created earlier as an argument
to SetActiveSource. Observe the change in the pipeline browser.
In addition to maintaining an active pipeline object, ParaView Python
scripting also maintains an active view. As a ParaView user, you should
also already be familiar with multiple views and the active view. The
active view is marked in the GUI with a blue border. The Python
functions GetActiveView and SetActiveView allow you to query and
change the active view. As with pipeline objects, the active view is
synchronized between the GUI and the Python interpreter.
This tutorial, as well as similar instructions in the ParaView book and
Wiki, is designed to give the key concepts necessary to understand and
create batch Python scripts. The detailed documentation including
complete lists of functions, classes, and properties available is
maintained by the ParaView build process and provided as online help
from within the ParaView application. In this way we can ensure that the
documentation is up to date for whatever version of ParaView you are
using and that it is easily accessible.
The ParaView Python bindings make use of the help built-in function.
This function takes as an argument any Python object and returns some
documentation on it. For example, typing
help(paraview.simple)
returns a brief description of the module and then a list of all the
functions included in the module with a brief synopsis of what each one
does. For example
help(Sphere)sphere=Sphere()help(sphere)
will first give help on the Sphere function, then use it to create
an object, and then give help on the object that was returned (including
a list of all the properties for the proxy).
Most of the widgets displayed in the properties panel’s Properties group
are automatically generated from the same introspection that builds the
Python classes. (There are a small number of exceptions where a custom
panel was created for better usability.) Thus, if you see a labeled
widget in the properties panel, there is a good chance that there is a
corresponding property in the Python object with the same name.
Regardless of whether the GUI contains a custom panel for a pipeline
object, you can still get information about that object’s properties
from the GUI’s online help. As always, bring up the help with the
toolbar button. You can find documentation for all the available
pipeline objects under the Sources, Filters, Readers, and Writers
entries in the help Contents. Each entry gives a list of objects of that
type. Clicking on any one of the objects gives a list of the properties
you can set from within Python.
The equivalent to opening a file in the ParaView GUI is to create a
reader in Python scripting. Reader objects are created in much the same
way as sources and filters; paraview.simple has a function for each
reader type that creates the pipeline object and returns a proxy object.
One can instantiate any given reader directly as described below, or
more simply call reader=OpenDataFile({filename})
All reader objects have at least one property (hidden in the GUI) that
specifies the file name. This property is conventionally called either
FileName or FileNames. You should always specify a valid file
name when creating a reader by placing something like
FileName={fullpath} in the arguments of the
construction object. Readers often do not initialize correctly if not
given a valid file name.
(Creating a Reader)
We are going to start a fresh visualization, so if you have been following
along with the exercises so far, now is a good time to reset ParaView.
The easiest way to do this is to select from the toolbar.
You will also need the Python shell. If you have not already done so,
open it with View → Python Shell from the menu.
In this exercise we are loading the disk_out_ref.ex2 file from the
Python shell. Locate this file on your computer and be ready to type or
copy it into the Python shell. We will reference it as
{path}/disk_out_ref.ex2. You can use the file browser to
help you locate this file. (Click on the Examples quick access directory
and observe where the file browser takes you.) Common paths for the file
are as follows:
In addition to having properties specific to the class, all proxies for
pipeline objects share a set of common properties and methods. Two very
important such properties are the PointData and CellData
properties. These properties act like dictionaries, an associative
array type in Python, that maps variable names (in strings) to
ArrayInformation objects that hold some characteristics of the
fields. Of particular note are the ArrayInformation methods
GetName, which returns the name of the field,
GetNumberOfComponents, which returns the size of each field value (1
for scalars, more for vectors), and GetRange, which returns the
minimum and maximum values for a particular component.
(Getting Field Information)
This exercise is a continuation of Exercise 3.8.
You will need to finish that exercise before beginning this one.
To start with, get a handle to the point data and print out all of the
point fields available.
pd=reader.PointDataprint(pd.keys())
Get some information about the “pres” and “v” fields.
Representations are the “glue” between the data in a pipeline object and
a view. The representation is responsible for managing how a data set is
drawn in the view. The representation defines and manages the underlying
rendering objects used to draw the data as well as other rendering
properties such as coloring and lighting. Parameters made available in
the Display group of the GUI are managed by representations. There is a
separate representation object instance for every pipeline-object–view
pair. This is so that each view can display the data differently.
Representations are created automatically by the GUI. In python
scripting they are created with the Show function instead. In fact
Show returns a proxy to the representation. Therefore you can save
Show’s return value in a variable as we’ve done above for sources,
filters and readers. If you neglect to save it, you can always get it
back with the GetRepresentation function. With no arguments, this
function will return the representation for the active pipeline object
and the active view. You can also specify a pipeline object or view or
both.
(Coloring Data)
This exercise is a continuation of Exercise 3.8
(and optionally Exercise 3.9).
If you do not have the exodus file open, you will need to finish
Exercise 3.8 before beginning this one.
Let us change the color of the geometry to blue and give it a very
pronounced specular highlight (that is, make it really shiny). Type in
the following into the Python shell to get the representation and change
the material properties.
Now rotate the camera with the mouse in the GUI to see the effect of the
specular highlighting.
We can also use the representation to color by a field variable. There
is actually quite a bit of state that must be set to change field
variables. The ColorBy function provides a simple interface to color
a mesh by a field value. A subsequent call to UpdateScalarBars also
updates the color bar annotation. Enter the following into the Python
shell to color the mesh by the “pres” field variable.
Drawing areas or windows are called Views in ParaView. As with readers,
sources, filters, and representations, views are wrapped into python
objects and these can be created, obtained and controlled via scripts.
Views are usually created for you by the GUI, but in python you have to
create views more intentionally. The most convenient way to do so is to
rely on the way that Render returns a view, creating one first if
necessary. If you prefer, you can create specific view types via
CreateView(’{viewname}’) or CreateRenderView,
CreateXYPlotView and the like. However you make them, call
GetRenderViews to get a list of all Views, or GetActiveView get
access to the currently active view. There is also a function named
GetRenderView (no ‘s’ on the end) that gets the active view if
there is one or creates a new one if there is no active view.
Once you have a view you have access to all of the properties that you
see on the View group of the GUI. For instance you can easily turn on
and off the orientation widget, change the background color, alter the
lighting and more. Besides these first level properties, the view also
gives you access to other scene wide controls such as the camera,
animation time, and when not running alongside the GUI, the view’s size.
(Controlling the View)
This exercise is a continuation of Exercise 3.8 (and optionally
Exercise 3.9, and Exercise 3.10.
If you do not have the exodus file open, you will need to finish
Exercise 3.8 before beginning this one.
Let us change the background color of the scene from ParaView’s default
gray to a nice gradient instead. Type the following into the Python
shell to get a hold of the View and change it.
Within a script it is easy to save out results, and by saving your data
and your scripts it becomes easy to create reproducible visualization
with ParaView.
As within the GUI, there are several products that you might like to
save out when you are working with ParaView.
To save out the data produced by a filter, add a writer to the filter
with the desired filename using the CreateWriter function and
then update the writer proxy with the UpdatePipeline method. This
is analogous to clicking on a pipeline element and selecting File
→ Save Data.
Saving images is as simple as typing
SaveScreenshot(’{path}/filename.still_extension’).
Assuming your ParaView is linked to an encoder and codecs, saving
compressed animations is as simple as typing
WriteAnimation(’{path}/filename.animation_extension’).
In all cases ParaView uses the file name extension to determine the
specific file type to create.
(Save Results)
This exercise is a continuation of Exercise 3.8 (and
optionally Exercise 3.9 through
Exercise 3.11). If you do not have the exodus file open,
you will need to finish Exercise 3.8 before beginning
this one.
Let us first probe the data to get something compact out of it. Then we
will save out the result of the probe in the form of a comma separated
values file so that we can look at it in a text editor and import it
into any other tool we choose.
As you can see, ParaView’s scripting interface is quite powerful, and
once you know the fundamentals and are familiar with Python’s syntax, it
is fairly easy to get up and running with it. We have just touched on
the higher level aspects of ParaView scriptability in this tutorial.
More details, including how to run python scripted filters, how to work
with numpy and other tools, and how to package your scripts for
execution under batch schedulers can be found online.
ParaView is used frequently at Sandia National Laboratories and other
institutions for visualizing data from large-scale simulations run on
the world’s largest supercomputers including the examples shown here.
CTH shock physics simulation with over 1 billion cells of a 10 megaton explosion
detonated at the center of the Golevka asteroid.
SEAM Climate Modeling simulation with 1 billion cells modeling the breakdown of the
polar vortex, a circumpolar jet that traps polar air at high latitudes.
A CTH simulation that generates AMR data. ParaView has been used to visualize
CTH simulation AMR data comprising billions of cells, 100’s of thousands
of blocks, and eleven levels of hierarchy (not shown).
A VPIC simulation of magnetic reconnection with 3.3 billion structured cells.
Image courtesy of Bill Daughton, Los Alamos National Laboratory.
A large scale in-situ PHASTA simulation that generated a 3.3 billion tetrahedral mesh
simulating the flow over a full wing where a synthetic jet issues an unsteady
crossflow jet (run on 160 thousand MPI processes).
A large scale in-situ PHASTA simulation that generated a 1.3 billion element mesh simulating the
wake of a deflected wing flap (run on 256 thousand MPI processes).
Images courtesy of Michel Rasquin, Argonne National Laboratory.
In this section we discuss visualizing large meshes like these using the
parallel visualization capabilities of ParaView. This section has some
exercises, but is less “hands-on” than the previous section. Primarily
you will learn the conceptual knowledge needed to perform large parallel
visualization. The exercises demonstrate the basic techniques needed to
run ParaView on parallel machines.
The most fundamental idea to grasp is that when run on a large machine
every node processes different regions of the entire dataset
simultaneously. Thus the workable data resolution is limited by the
aggregate memory space of the machine. We now present the basic ParaView
architecture and parallel algorithms and demonstrate how to apply this
knowledge.
We are fortunate in visualization in that many operations are
straightforward to parallelize. The data we deal with is contained in a
mesh, which means the data is already broken into little pieces by the
cells. We can do visualization on a distributed parallel machine by
first dividing the cells among the processes. For demonstrative
purposes, consider this very simplified mesh.
Now let us say we want to perform visualizations on this mesh using
three processes. We can divide the cells of the mesh as shown below with
the blue, yellow, and pink regions.
Once partitioned, many visualization algorithms will work by simply
allowing each process to independently run the algorithm on its local
collection of cells. For example, take clipping (which is demonstrated
in multiple exercises including Exercise 2.11). Let us say that
we define a clipping plane and give that same plane to each of the
processes.
Each process can independently clip its cells with this plane. The end
result is the same as if we had done the clipping serially. If we were
to bring the cells together (which we would never actually do for large
data for obvious reasons) we would see that the clipping operation took
place correctly.
Many, but not all operations are thus trivially parallizeable. Other
operations are straightforward to parallelize if ghost layers as
described in Section 4.7.2 are available. Other
operations require more extensive data sharing among nodes. In these
filters ParaView resorts to MPI to communicate amongst the nodes of the
machine.
When performing parallel visualization, we are careful to ensure that
the data remains partitioned among all of the processes up to and
including the rendering processes. ParaView uses a parallel rendering
library called IceT. IceT uses a sort-last algorithm for
parallel rendering. This parallel rendering algorithm has each process
independently render its partition of the geometry and then
composites the partial images together to form the final image.
The preceding diagram is an oversimplification. IceT contains multiple
parallel image compositing algorithms such as binary tree, binary
swap, and radix-k that efficiently divide work among processes
using multiple phases.
The wonderful thing about sort-last parallel rendering is that its
efficiency is completely insensitive to the amount of data being
rendered. This makes it a very scalable algorithm and well suited to
large data. However, the parallel rendering overhead does increase
linearly with the number of pixels in the image. This can be a problem
for example when driving tile display walls with ParaView. Consequently,
some of the rendering parameters described later in this chapter deal
with limiting image size.
Because there is an overhead associated with parallel rendering,
ParaView can also render serially and will do so automatically when the
visible data is small enough. When the visible meshes are smaller than a
user defined threshold preference, or when parallel rendering is turned
off or unavailable, the geometry is shipped to the display node, which
then rasterizes it locally. Obviously, this should only happen when the
data being rendered is small or the rendering process will be
overwhelmed.
With this introduction to parallel visualization, it is useful to know
something about how ParaView is structured and how it orchestrates the
parallel tasks described above.
ParaView is designed as a three-tier client-server architecture. The
three logical units of ParaView are as follows.
Data Server
The unit responsible for data reading, filtering, and writing. All of
the pipeline objects seen in the pipeline browser are contained in
the data server. The data server can be parallel.
Render Server
The unit responsible for rendering. The render server can also be
parallel, in which case built in parallel rendering is also enabled.
Client
The unit responsible for establishing visualization. The client
controls the object creation, execution, and destruction in the
servers, but does not contain any of the data (thus allowing the
servers to scale without bottlenecking on the client). If there is a
GUI, that is also in the client. The client is always a serial
application.
These logical units need not be physically separated. Logical units are
often embedded in the same application, removing the need for any
communication between them. There are three modes in which you can run
ParaView. Note that no matter what mode ParaView runs in the user
interface and scripting API that you learned in Section 2
and Section 3 undergoes very little change.
The first mode, which you are already familiar with, is standalone
mode. In standalone mode, the client, data server, and render server are
all combined into a single serial application. When you run the
paraview application, you are automatically connected to a
builtin server so that you are ready to use the full features of
ParaView.
The second mode is client-server mode. In client-server mode, you
execute the pvserver program on a parallel machine and connect to it
with the paraview client application. The pvserver program has
both the data server and render server embedded in it, so both data
processing and rendering take place there. The client and server are
connected via a socket, which is assumed to be a relatively slow mode of
communication, so data transfer over this socket is minimized.
The third mode is client–render-server–data-server mode. In this
mode, all three logical units are running in separate programs. As
before, the client is connected to the render server via a single socket
connection. The render server and data server are connected by many
socket connections, one for each process in the render server. Data
transfer over the sockets is minimized.
Although the client-render server-data server mode is supported, we
almost never recommend using it. The original intent of this mode was to
take advantage of heterogeneous environments where one might have a
large, powerful computational platform and a second smaller parallel
machine with graphics hardware in it. However, in practice we find any
benefit is almost always outstripped by the time it takes to move
geometry from the data server to the render server. If the computational
platform is much bigger than the graphics cluster, then use software
rendering on the large computational platform. If the two platforms are
about the same size just perform all the computation on the graphics
cluster.
Accessing a standalone installation of ParaView is trivial. Download and
install a pre-compiled binary or get it from your package manager, and
go. To visualize extreme scale results, you need to access an
installation of ParaView, built with the MPI components enabled, on a
machine with sufficient aggregate memory to hold the entire data set and
derived data products. Accessing a parallel enabled installation of
ParaView’s server is intrinsically harder than acessing a standalone
version.
Recent binary distributions of ParaView provided by Kitware do include
MPI for Mac, Linux and optionally Windows. The Windows MPI enabled
binaries depend upon Microsoft’s MPI, which must be installed
separately. We will not cover those in the rest of this tutorial, but
feel free to ask questions on the ParaView mailing list.
Note that the specific MPI library version bundled into the binaries
were chosen for widest possible compatibility. For production use
ParaView will be much more effective when compiled with an MPI version
that is tuned for your machine’s networking fabric. Your system
administrators can help you decide what MPI version to use.
To compile ParaView on a parallel machine you or your system
administrators will need the following.
OpenGL, either using a GPU in on- (X11) or off- screen (EGL) modes,
or in software via Mesa.
Python +NumPy +Matplotlib (all optional but strongly recommended)
Qt \(\ge\) 4.7 (optional)
Compiling without one of the optional libraries means a feature will not
be available. Compiling without Qt means that you will not have the GUI
application and compiling without Python means that you will not have
scripting available. NumPy is almost as important as Python itself, and
Matplotlib is helpful for numeric text and some types of views and color
lookup tables.
To compile ParaView, you first run CMake, which will allow you to set up
compilation parameters and point to libraries on your system. This will
create the make files that you then use to build ParaView. For more
details on building a ParaView server, see the ParaView Wiki.
Compiling ParaView on exotic machines, for example HPC class machines
that require cross compilation and some cloud-based on demand systems,
can be an arduous task. You are welcome to seek free advice on the
ParaView mailing list or contracted assistance from Kitware.
Fortunately there are a number of large scale systems on which ParaView
has already been installed. If you are fortunate enough to have an
account on one of these systems, you shouldn’t need to compile anything.
The ParaView community maintains an opt in list of these with pointers
to system specific documentation on the ParaView Wiki. We invite system
maintainers to add to the list if they are permitted to.
Running ParaView in parallel is also intrinsically more difficult than
running the standalone client. It typically involves a number of steps
that change depending on the hardware you are running on: logging in to
remote computers, allocating parallel nodes, launching a parallel
program, and sometimes tunneling through firewalls to establish
interactive connections to the compute nodes. These steps are discussed
in more detail in the next two sections in which we finally return from
theory to practical exercises.
ParaView’s Python scripted interface, introduced in
Section 3 has the important qualities of being
runnable offline, with the human removed from the loop, and being inherently
reproducible.
On large scale systems there are two steps that you need to master. The
first is to run ParaView in parallel through MPI. The second is to
submit a job through the system’s queuing system. For both steps the
syntax varies from machine to machine and you should consult your
system’s documentation for the details.
We demonstrate how to run ParaView in parallel with the simplest case of
running Kitware’s binary in parallel on the PC class system that you
have at hand.
(Running a visualization script in parallel)
You will need three things, the mpiexec program to spawn MPI parallel
programs, the pvbatch executable and a Python script.
As for the Python script, let us use an example in which each node draws
a portion of a simple polygonal sphere with a color map that varies over
the number of processes in the job.
Use an editor to type this script into a file called parasphere.py and
save it somewhere. Note this is a stripped down version of a script
recorded from a parallel ParaView session in which we created a
Sources → Sphere and chose the vtkProcessId array to color by.
As for the executables, let us use the ones that come with ParaView.
After installing Kitware’s ParaView binaries, you will find mpiexec
and pvbatch at:
On Linux and assuming you have extracted the binary into /usr/local:
/usr/local/lib/paraview-x.x.x/mpiexec
and
/usr/local/bin/pvbatch
Note that you will need to add ParaView’s lib directory
(/usr/local/lib/paraview-x.x.x) to your LD_LIBRARY_PATH to use the
mpi that comes with ParaView.
On Windows and assuming you installed the “MPI” version of ParaView
as well as the MS-MPI software (available separately from Microsoft
for free):
C:/Program Files/Microsoft MPI/Bin/mpiexec
and
C:/Program Files/ParaView x.x.x/bin/pvbatch
Now we run the script in parallel by issuing this from the command line.
ParaView will run momentarily and it may or may not briefly display a
window on your desktop. In any case you will now find a file named
parasphere.png that looks like the following:
Submitting a job through your system’s queuing system typically involves
issuing a command like the following on the command line.
qsub -A <project name to charge to compute time to> \ -N <number of nodes> \ -n <number of processors on each node> \ mpiexec -np <N*n> \ pvbatch <arguments for pvbatch> \ script_to_execute.py <arguments for Python script>
The command reserves the requested number of compute nodes on the
machine and, at some time in the future when the nodes become ready for
your use, spawns an MPI job. The MPI job runs ParaView’s Python scripted
server in parallel, telling it to process the supplied script.
There are many queuing systems and mpi implementations and site specific
policies. Thus it it impossible to provide an exact syntax that will
work on every system here. Ask your system administrators for guidance.
Once you have the syntax, you should be able to run the sphere example
above to determine if you have a working system.
For day to day work with large datasets it is feasible to do interactive
visualization in parallel too. In this mode you can dynamically inspect
the data and modify the visualization pipeline while you work with the
ParaView GUI on a workstation far from the HPC resource where the
data is being processed.
In interactive configurations the data processing and rendering portions
work in parallel like above but they are controlled from the ParaView
GUI instead of a Python script.
Starting the server process is similar to the above, but instead of
using the pvbatch executable we use the pvserver executable. The
former is limited to taking commands from Python scripts, the later is
built to take commands from a remote ParaView GUI program.
Client-server connections are established through the paraview
client application. You connect to servers and disconnect from servers
with the and buttons. When ParaView starts,
it automatically connects to the builtin server. It also connects to
builtin whenever it disconnects from a server.
When you hit the button, ParaView presents you with a dialog
box containing a list of known servers you may connect to. This list of
servers can be both site- and user-specific.
You can specify how to connect to a server either through the GUI by
pressing the Add Server button or through an XML definition file. There
are several options for specifying server connections, but ultimately
you are giving ParaView a command to launch the server and a host to
connect to after it is launched.
Once more we will demonstrate using the Kitware binaries and then
outline the steps required on large scale systems where the syntax
varies widely.
(Interactive Parallel Visualization)
The pvserver executable can be found in the same directory as the
pvbatch exectuable. Let us begin by running it in parallel.
Now start up the ParaView GUI and click the button. This will
bring the Choose Server Configuration dialog box where you can download or
create server connection paths, or connect to predefined paths.
Now click the Add Server button to create a new path, which we will
construct to connect to the waiting pvserver running on your local
machine.
In the Edit Server Configuration Dialog, change the Name of the
connection path from “unknown” to “my computer”. In actual use one would
enter in a nickname for and the IP address of the remote machine we want
to connect to. Now hit the Configure button.
On the resulting Edit Server Launch Configuration dialog, leave the
Startup Type as Manual since we have already started a waiting
pvserver. In actual use one would typically use Command and in the
dialog enter in a script that starts up the server on the remote
machine. Click Save on the dialog to finish defining the connection.
Now that we have defined a connection, it will show up under the Choose
Server Configuration dialog whenever we hit . Click on the name of the
connection, “my computer” in this case, and click Connect to establish
the connection between the GUI and pvserver.
Once connected, simply File → Open files on the
remote system and work with them as before. To complete the exercise,
open or create a data set, and choose the vtkProcessId array to examine
how it is partioned across the distributed memory of the server.
In practice, the syntax of starting up a parallel server on a remote
machine and connecting to it will be more involved. Typically the steps
include ssh’ing to a remote machine’s login node, submitting a job that
runs a script that requests some number of nodes and runs pvserver
under MPI on them with pvserver made to connect back to the waiting
client (instead of the reverse as above) over at least one ssh tunnel
hops. System administrators and other adventurous folk can find details
online here:
On the local machine you may need helper utilities as well. XQuartz (for
X11) on Mac and Putty (for ssh) on Windows are useful for starting up
remote connections. These are required to complete the next exercise.
Once a connection is established the steps should be saved in scripts
and configuration files. System administrators can publish these so that
authorized users can simply download and use them. Several of these
configuration files are hosted on the ParaView website where the
ParaView client can download them from.
(Fetching and using Connections)
Once again, click on to bring up the Choose Server Configuration dialog.
This time, hit the Fetch Servers button. This will bring up the Fetch
Server Configurations dialog box populated with a list of server definitions
from the webite. Choose one and click the Import Selected button to download
it into your ParaView preferences. The new connection is now available
just as the connection to “my computer” is.
To use the remote machine, once more click . This time choose the new
machine instead of “my machine” and click Connect. Doing so will bring
up a Connection Options for … dialog box that lets where you enter in
the parameters for your parallel session.
The parameters you will want to set include your username on the remote
machine, the number of nodes and processes to reserve and the amount of
time you want to reserve them for. Each site may have additional choices
that are passed into the launch scripts on the server. Once set, click
OK to try to establish a connection.
When you click OK ParaView typically spawns a terminal window (xterm on
Mac and Linux, cmd.exe on Windows). Here you will have to enter in your
credentials to actually access the remote machine. Once logged on, the
script to reserve the nodes automatically runs and in most cases the
terminal session has a menu with options for looking at the remote
system’s queue. When your job reaches the top of the queue, the ParaView
3D View window will return and you can begin doing remote visualization,
this time with the capacity of the remote machine at your fingertips.
When working with very large models, it is important to keep track of
memory usage on the computer. One of the most common and frustrating
problems encountered with large models is running out of memory. This in
turn will lead to thrashing in the virtual memory system or an outright
program fault.
Section 4.8.2 and Section 4.8.3 provide
suggestions to reduce your memory usage. Even so, it is wise to keep an
eye on the memory available in your system. ParaView provides a tool
called the memory inspector designed to do just that.
To access the memory inspector, select in the menu bar View
→ Memory Inspector. The memory inspector provides
information for both the client you are running on and any server you
might be connected to. It will tell you the total amount of memory used
on the system and the amount of memory ParaView is using. For servers
containing multiple nodes, information both for the conglomerate job and
for each individual node are given. Note that a memory issue in any
single node can cause a problem for the entire ParaView job.
Unfortunately, blindly running visualization algorithms on partitions of
cells does not always result in the correct answer. As a simple example,
consider the external faces algorithm. The external faces algorithm
finds all cell faces that belong to only one cell, thereby identifying
the boundaries of the mesh. What happens when we run external faces
independently on our partitions?
Oops. We see that when all the processes ran the external faces
algorithm independently, many internal faces were incorrectly identified
as being external. This happens where a cell in one partition has a
neighbor in another partition. A process has no access to cells in other
partitions, so there is no way of knowing that these neighboring cells
exist.
The solution employed by ParaView and other parallel visualization
systems is to use ghost cells (sometimes also called halo
regions). Ghost cells are cells that are held in one process but
actually belong to another. To use ghost cells, we first have to
identify all the neighboring cells in each partition. We then copy these
neighboring cells to the partition and mark them as ghost cells, as
indicated with the gray colored cells in the following example.
When we run the external faces algorithm with the ghost cells, we see
that we are still incorrectly identifying some internal faces as
external. However, all of these misclassified faces are on ghost cells,
and the faces inherit the ghost status of the cell it came from.
ParaView then strips off the ghost faces and we are left with the
correct answer.
In this example we have shown one layer of ghost cells: only those cells
that are direct neighbors of the partition’s cells. ParaView also has
the ability to retrieve multiple layers of ghost cells, where each layer
contains the neighbors of the previous layer not already contained in a
lower ghost layer or the original data itself. This is useful when we
have cascading filters that each require their own layer of ghost cells.
They each request an additional layer of ghost cells from upstream, and
then remove a layer from the data before sending it downstream.
For the most part, ParaView leaves the task of breaking up or
partitioning the data to the simulation code that produced the data. It
is then the responsibility of ParaView’s specific reader module for the
file format in question to work efficiently, typically reading different
files from different nodes independently but simultaneously. In ideal
cases the rest of the parallel pipeline also operates independently and
simultaneously.
Still, in the general case, since we are breaking up and distributing
our data, it is prudent to address the ramifications of how we partition
the data. The data shown in Section 4.1 has a
spatially coherent partitioning. That is, all the cells of each
partition are located in a compact region of space. There are other ways
to partition data. For example, you could have a random partitioning.
Random partitioning has some nice features. It is easy to create and is
friendly to load balancing. However, a serious problem exists with
respect to ghost cells.
In this example, we see that a single level of ghost cells nearly
replicates the entire data set on all processes. We have thus removed
any advantage we had with parallel processing. Because ghost cells are
used so frequently, random partitioning is not used in ParaView.
The previous sections described the importance of load balancing and
ghost levels for parallel visualization. This section describes how to
achieve that.
Load balancing and ghost cells are handled automatically by ParaView
when you are reading structured data (image data, rectilinear grid, and
structured grid). The implicit topology makes it easy to break the data
into spatially coherent chunks and identify where neighboring cells are
located.
It is an entirely different matter when you are reading in unstructured
data (poly data and unstructured grid). There is no implicit topology
and no neighborhood information available. ParaView is at the mercy of
how the data was written to disk. Thus, when you read in unstructured
data there is no guarantee about how well load balanced your data will
be. It is also unlikely that the data will have ghost cells available,
which means that the output of some filters may be incorrect.
Fortunately, ParaView has a filter that will both balance your
unstructured data and create ghost cells. This filter is called D3,
which is short for distributed data decomposition. Using D3 is easy;
simply attach the filter (located in Filters
→ Alphabetical → D3) to whatever
data you wish to repartition.
The most common use case for D3 is to attach it directly to your
unstructured grid reader. Regardless of how well load balanced the
incoming data might be, it is important to be able to retrieve ghost
cells so that subsequent filters will generate the correct data. The
example above shows a cutaway of the extract surface filter on an
unstructured grid. On the left we see that there are many faces
improperly extracted because we are missing ghost cells. On the right
the problem is fixed by first using the D3 filter.
In many cases a better alternative to D3 filter is the Ghost Level
Generator. This filter is more efficient than the D3 filter because it
makes the assumption that the input unstructured grid data is already
partitioned into spatially coherent regions. This is generally a safe
assumption as simulations benefit from coherency too. Because of this,
it concerns itself only with cells at and near the external shell of the
mesh, and does not consider or transfer the bulk of the data at the
interior.
How many cores should I have in my |ParaView| server? This is a common
question with many important ramifications. It is also an enormously
difficult question. The answer depends on a wide variety of factors
including what hardware each processor has, how much data is being
processed, what type of data is being processed, what type of
visualization operations are being done, and your own patience.
Consequently, we have no hard answer. We do however have several rules
of thumb.
If you are loading structured data (image data, rectilinear grid,
structured grid), try to have a minimum of one core per 20 million
cells. If you can spare the cores, one core for every 5 to 10 million
cells is usually plenty.
If you are loading unstructured data (poly data, unstructured grid),
try to have a minimum of one core per 1 million cells. If you can spare
the cores, one core for every 250 to 500 thousand cells is usually
plenty.
As stated before, these are just rules of thumb, not absolutes. You
should always try to experiment to gage what your core to data size
should be. And, of course, there will always be times when the data you
want to load will stretch the limit of the resources you have available.
When this happens, you will want to make sure that you avoid data
explosion and that you cull your data quickly.
The pipeline model that ParaView presents is very convenient for
exploratory visualization. The loose coupling between components
provides a very flexible framework for building unique visualizations,
and the pipeline structure allows you to tweak parameters quickly and
easily.
The downside of this coupling is that it can have a larger memory
footprint. Each stage of this pipeline maintains its own copy of the
data. Whenever possible, ParaView performs shallow copies of the
data so that different stages of the pipeline point to the same block of
data in memory. However, any filter that creates new data or changes the
values or topology of the data must allocate new memory for the result.
If ParaView is filtering a very large mesh, inappropriate use of filters
can quickly deplete all available memory. Therefore, when visualizing
large data sets, it is important to understand the memory requirements
of filters.
Please keep in mind that the following advice is intended only for when
dealing with very large amounts of data and the remaining available
memory is low. When you are not in danger of running out of memory,
ignore all of the following advice.
When dealing with structured data, it is absolutely important to know
what filters will change the data to unstructured. Unstructured data has
a much higher memory footprint, per cell, than structured data because
the topology must be explicitly written out. There are many filters in
ParaView that will change the topology in some way, and these filters
will write out the data as an unstructured grid, because that is the
only data set that will handle any type of topology that is generated.
The following list of filters will write out a new unstructured topology
in its output that is roughly equivalent to the input. These filters
should never be used with structured data and should be used with
caution on unstructured data.
Append Datasets
Append Geometry
Clean
Clean to Grid
Connectivity
D3
Delaunay 2D/3D
Extract Edges
Linear Extrusion
Loop Subdivision
Reflect
Rotational Extrusion
Shrink
Smooth
Subdivide
Tessellate
Tetrahedralize
Triangle Strips
Triangulate
Technically, the Ribbon and Tube filters should fall into this list.
However, as they only work on 1D cells in poly data, the input data is
usually small and of little concern.
This similar set of filters also output unstructured grids, but they
also tend to reduce some of this data. Be aware though that this data
reduction is often smaller than the overhead of converting to
unstructured data. Also note that the reduction is often not well
balanced. It is possible (often likely) that a single process may not
lose any cells. Thus, these filters should be used with caution on
unstructured data and extreme caution on structured data.
Clip
Decimate
Extract Cells by Region
Extract Selection
Quadric Clustering
Threshold
Similar to the items in the preceding list, Extract Subset performs
data reduction on a structured data set, but also outputs a structured
data set. So the warning about creating new data still applies, but you
do not have to worry about converting to an unstructured grid.
This next set of filters also outputs unstructured data, but it also
performs a reduction on the dimension of the data (for example 3D to
2D), which results in a much smaller output. Thus, these filters are
usually safe to use with unstructured data and require only mild caution
with structured data.
Cell Centers
Contour
Extract CTH Parts
Extract Surface
Feature Edges
Mask Points
Outline (curvilinear)
Slice
Stream Tracer
These filters do not change the connectivity of the data at all.
Instead, they only add field arrays to the data. All the existing data
is shallow copied. These filters are usually safe to use on all data.
Block Scalars
Calculator
Cell Data to Point Data
Curvature
Elevation
Generate Surface Normals
Gradient
Level Scalars
Median
Mesh Quality
Octree Depth Limit
Octree Depth Scalars
Point Data to Cell Data
Process Id Scalars
Python Calculator
Random Vectors
Resample with dataset
Surface Flow
Surface Vectors
Texture Map to…
Transform
Warp (scalar)
Warp (vector)
This final set of filters are those that either add no data to the
output (all data of consequence is shallow copied) or the data they add
is generally independent of the size of the input. These are almost
always safe to add under any circumstances (although they may take a lot
of time).
Annotate Time
Append Attributes
Extract Block
Extract Level
Glyph
Group Datasets
Histogram
Integrate Variables
Normal Glyphs
Outline
Outline Corners
Plot Global Variables Over Time
Plot Over Line
Plot Selection Over Time
Probe Location
Temporal Shift Scale
Temporal Snap-to-Time-Steps
Temporal Statistics
There are a few special case filters that do not fit well into any of
the previous classes. Some of the filters, currently Temporal
Interpolator and Particle Tracer, perform calculations based on how data
changes over time. Thus, these filters may need to load data for two or
more instances of time, which can double or more the amount of data
needed in memory. The Temporal Cache filter will also hold data for
multiple instances of time. Also keep in mind that some of the temporal
filters such as the temporal statistics and the filters that plot over
time may need to iteratively load all data from disk. Thus, it may take
an impractically long amount of time even though it does not require any
extra memory.
The Programmable Filter is also a special case that is impossible to
classify. Since this filter does whatever it is programmed to do, it can
fall into any one of these categories.
When dealing with large data, it is clearly best to cull out data
whenever possible, and the earlier the better. Most large data starts as
3D geometry and the desired geometry is often a surface. As surfaces
usually have a much smaller memory footprint than the volumes that they
are derived from, it is best to convert to a surface soon. Once you do
that, you can apply other filters in relative safety.
A very common visualization operation is to extract isosurfaces from a
volume using the Contour filter. The Contour filter usually outputs
geometry much smaller than its input. Thus, the Contour filter should be
applied early if it is to be used at all. Be careful when setting up the
parameters to the Contour filter because it still is possible for it to
generate a lot of data. This obviously can happen if you specify many
isosurface values. High frequencies such as noise around an isosurface
value can also cause a large, irregular surface to form.
Another way to peer inside of a volume is to perform a Slice on it. The
Slice filter will intersect a volume with a plane and allow you to see
the data in the volume where the plane intersects. If you know the
relative location of an interesting feature in your large data set,
slicing is a good way to view it.
If you have little a-priori knowledge of your data and would like to
explore the data without paying the memory and processing time for the
full data set, you can use the Extract Subset filter to subsample the
data. The subsampled data can be dramatically smaller than the original
data and should still be well load balanced. Of course, be aware that
you may miss small features if the subsampling steps over them and that
once you find a feature you should go back and visualize it with the
full data set.
There are also several features that can pull out a subset of a volume:
Clip , Threshold , Extract Selection ,
and Extract Subset can all extract cells based on some criterion.
Be aware, however, that the extracted cells are almost never well balanced; expect
some processes to have no cells removed. Also, all of these filters with the exception
of Extract Subset will convert structured data types to unstructured
grids. Therefore, they should not be used unless the extracted cells are
of at least an order of magnitude less than the source data.
When possible, replace the use of a filter that extracts 3D data with
one that will extract 2D surfaces. For example, if you are interested in
a plane through the data, use the Slice filter rather than the Clip
filter. If you are interested in knowing the location of a region of
cells containing a particular range of values, consider using the
Contour filter to generate surfaces at the ends of the range rather
than extract all of the cells with the Threshold filter. Be aware that
substituting filters can have an effect on downstream filters. For
example, running the Histogram filter after Threshold will
have an entirely different effect than running it after the roughly equivalent
Contour filter.
Downsampling is also frequently helpful for very large data. For example,
the Extract Subset filter reduce the size of Structured DataSets by
simpling taking strided samples along the i, j and k axes.
For unstructured grids the Quadric Clustering filter downsamples
unstructured data into a smaller dataset with similar appearance by
averaging vertices within cells of a grid. ParaView injects this
algorithm into the display pipeline while you interact with the camera
as described in the next section.
In some cases though, it can be more effective to work with structured
data than unstructured data. In particular structured data volume
rendering algorithms are usually much faster. In general structured data
representations are very compact, adding very little overhead to the raw
data values. Unstructured data types require 12 bytes of memory storage
for every vertex and at least 8 bytes of storage to define each cell
beyond the normal storage for cell and point aligned values. Structured
types use a total of 36 bytes to represent the entire set of vertices
and cells in comparison.
Fortunately you can convert from unstructured to structured easily with
the Resample To Image filter. When the sizes of the cells in the input
do not very widely, and can thus be approximated well by constant sized
voxels, this can be very effective. This filter internally makes use of
the DIY2 block-parallel communication and computation library to
communicate and transfer data among the parallel nodes.
There is a companion filter Resample With DataSet which takes in a
source and an input object and resamples values from the source onto the
input, which does not have to be a regular grid. This also uses DIY2.
This is used to assigning new values onto a particular shaped object.
Rendering is the process of synthesizing the images that you see based
on your data. The ability to effectively interact with your data depends
highly on the speed of the rendering. Thanks to advances in 3D hardware
acceleration, fueled by the computer gaming market, we have the ability
to render 3D quickly even on moderately priced computers. But, of
course, the speed of rendering is proportional to the amount of data
being rendered. As data gets bigger, the rendering process naturally
gets slower.
To ensure that your visualization session remains interactive, ParaView
supports two modes of rendering that are automatically flipped as
necessary. In the first mode, still render, the data is rendered at
the highest level of detail. This rendering mode ensures that all of the
data is represented accurately. In the second mode, interactive
render, speed takes precedence over accuracy. This rendering mode
endeavors to provide a quick rendering rate regardless of data size.
While you are interacting with a 3D view, for example rotating, panning,
or zooming with the mouse, ParaView uses an interactive render. This is
because during the interaction a high frame rate is necessary to make
these features usable and because each frame is immediately replaced
with a new rendering while the interaction is occurring so that fine
details are less important during this mode. At any time when
interaction of the 3D view is not taking place, ParaView uses a still
render so that the full detail of the data is available as you study it.
As you drag your mouse in a 3D view to move the data, you may see an
approximate rendering while you are moving the mouse, but the full
detail will be presented as soon as you release the mouse button.
The interactive render is a compromise between speed and accuracy. As
such, many of the rendering parameters concern when and how lower levels
of detail are used.
Some of the most important rendering options are the LOD parameters.
During interactive rendering, the geometry may be replaced with a lower
level of detail (LOD), an approximate geometry with fewer
polygons.
The resolution of the geometric approximation can be controlled. In the
proceeding images, the left image is the full resolution; the middle
image is the default decimation for interactive rendering, and the right
image is ParaView’s maximum decimation setting.
The 3D rendering parameters are located in the settings dialog box which
is accessed in the menu from Edit → Settings
(ParaView → Preferences on the Mac). The rendering
options in the dialog are in the Render View tab.
The options pertaining to the geometric decimation for interactive
rendering are located in a section labeled Interactive Rendering
Options. Some of these options are considered advanced, so to access
them you have to either toggle on the advanced options with the
button or search for the option using the edit box at the top of the dialog.
The interactive rendering options include the following.
Set the data size at which to use a decimated geometry in interactive
rendering. If the geometry size is under this threshold, ParaView
always renders the full geometry. Increase this value if you have a
decent graphics card that can handle larger data. Try decreasing this
value if your interactive renders are too slow.
Set the factor that controls how large the decimated geometry should
be. This control is set to a value between 0 and 1. 0 produces a very
small number of triangles but possibly with a lot of distortion. 1
produces more detailed surfaces but with larger geometry.
Add a delay between an interactive render and a still render.
ParaView usually performs a still render immediately after an
interactive motion is finished (for example, releasing the mouse
button after a rotation). This option can add a delay that can give
you time to start a second interaction before the still render
starts, which is helpful if the still render takes a long time to
complete.
Use an outline in place of decimated geometry. The outline is an
alternative for when the geometry decimation takes too long or still
produces too much geometry. However, it is more difficult to interact
with just an outline.
ParaView contains many more rendering settings. Here is a summary of
some other settings that can effect the rendering performance regardless
of whether ParaView is run in client-server mode or not. These options
are spread among several categories, and several are considered
advanced.
Geometry Mapper Options
Enable or disable the use of display lists. Display lists are
internal structures built by graphics systems. They can
potentially speed up rendering but can also take up memory.
Translucent Rendering Options
Enable or disable depth peeling. Depth peeling is a technique
ParaView uses to properly render translucent surfaces. With it,
the top surface is rendered and then “peeled away” so that the
next lower surface can be rendered and so on. If you find that
making surfaces transparent really slows things down or renders
completely incorrectly, then your graphics hardware may not be
implementing the depth peeling extensions well; try shutting off
depth peeling.
Set the maximum number of peels to use with depth peeling. Using
more peels allows more depth complexity but allowing less peels
runs faster. You can try adjusting this parameter if translucent
geometry renders too slow or translucent images do not look
correct.
Miscellaneous
When creating very large datasets, default to the outline
representation. Surface representations usually require ParaView
to extract geometry of the surface, which takes time and memory.
For data with size above this threshold, use the outline
representation, which has very little overhead, by default
instead.
Show or hide annotation providing rendering performance
information. This information is handy when diagnosing performance
problems.
Note that this is not a complete list of ParaView rendering settings. We
have left out settings that do not significantly effect rendering
performance. We have also left out settings that are only valid for
parallel client-server rendering, which are discussed in
Section 4.9.3.
The overhead incurred by the parallel rendering algorithms is
proportional to the size of the images being generated. Also, images
generated on a server must be transfered to the client, a cost that is
also proportional to the image size. To help increase the frame rate
during interaction, ParaView introduces a new LOD parameter that
controls the size of the images.
During interaction while parallel rendering, ParaView can optionally
subsample the image. That is, ParaView will reduce the resolution of the
image in each dimension by a factor during interaction. Reduced images
will be rendered, composited, and transfered. On the client, the image
is inflated to the size of the available space in the GUI.
The resolution of the reduced images is controlled by the factor with
which the dimensions are divided. In the preceding images, the left
image has the full resolution. The following images were rendered with
the resolution reduced by a factor of 2, 4, and 8, respectively.
ParaView also has the ability to compress images before transferring
them from server to client. Compression, of course, reduces the amount
of data transferred and therefore makes the most of the available
bandwidth. However, the time it takes to compress and decompress the
images adds to the latency.
ParaView contains three different image compression algorithms for
client-server rendering. The oldest is a custom algorithm called
Squirt, which stands for Sequential Unified Image Run Transfer.
Squirt is a run-length encoding compression that reduces color depth to
increase run lengths. The second algorithm uses the Zlib compression
library, which implements a variation of the Lempel-Ziv algorithm. Zlib
typically provides better compression than Squirt, but takes longer to
perform and hence adds to the latency. The most recent addition is the
LZ4 algorithm which is tuned for fast compression and decompression.
Like the other 3D rendering parameters, the parallel rendering
parameters are located in the settings dialog box, which is accessed in
the menu from Edit → Settings (ParaView
→ Preferences on the Mac). The parallel rendering
options in the dialog are in the Render View tab (intermixed with
several other rendering options such as those described in
Section 4.9.1). The parallel and
client-server options are divided among several categories, and several
are considered advanced.
Remote/Parallel Rendering Options
Set the data size at which to render remotely in parallel or to
render locally. If the geometry is over this threshold (and
ParaView is connected to a remote server), the data is rendered in
parallel remotely and images are sent back to the client. If the
geometry is under this threshold, the geometry is sent back to the
client and images are rendered locally on the client.
Set the sub-sampling factor for still (non-interactive) rendering.
Some large displays have more resolution than is really necessary,
so this sub-sampling reduces the resolution of all images
displayed.
Client/Server Rendering Options
Set the interactive subsampling factor. The overhead of parallel
rendering is proportional to the size of the images generated.
Thus, you can speed up interactive rendering by specifying an
image subsampling rate. When this box is checked, interactive
renders will create smaller images, which are then magnified when
displayed. This parameter is only used during interactive renders.
Image Compression
Before images are shipped from server to client, they optionally
can be compressed using one of the three compression algorithms:
Squirt, Zlib or LZ4. To make the compression more effective, each
algorithm has one or more tunable parameters that let you
customize the behavior and target level of compression.
Suggested image compression presets are provided for several
common network types. When attempting to select the best image
compression options, try starting with the presets that best match
your connection.
The default rendering parameters are suitable for most users. However,
when dealing with very large data, it can help to tweak the rendering
parameters. The optimal parameters depend on your data and the hardware
ParaView is running on, but here are several pieces of advice that you
should follow.
Try turning off display lists. Turning this option off will prevent
the graphics system from building special rendering structures. If
you have graphics hardware, these rendering structures are important
for feeding the GPUs fast enough. However, if you do not have GPUs,
these rendering structures do not help much.
If there is a long pause before the first interactive render of a
particular data set, it might be the creation of the decimated
geometry. Try using an outline instead of decimated geometry for
interaction. You could also try lowering the factor of the decimation
to 0 to create smaller geometry.
Avoid shipping large geometry back to the client. The remote
rendering will use the power of entire server to render and ship
images to the client. If remote rendering is off, geometry is shipped
back to the client. When you have large data, it is always faster to
ship images than to ship data (although if your network has a high
latency, this could become problematic for interactive frame rates).
Adjust the interactive image sub-sampling for client-server rendering
as needed. If image compositing is slow, if the connection between
client and server has low bandwidth, or if you are rendering very
large images, then a higher subsample rate can greatly improve your
interactive rendering performance.
Make sure Image Compression is on. It has a tremendous effect on
desktop delivery performance, and the artifacts it introduces, which
are only there during interactive rendering, are minimal. Lower
bandwidth connections can try using Zlib or LZ4 instead of Squirt
compression. Zlib will create smaller images at the cost of longer
compression/decompression times.
If the network connection has a high latency, adjust the parameters
to avoid remote rendering during interaction. In this case, you can
try turning up the remote rendering threshold a bit, and this is a
place where using the outline for interactive rendering is effective.
If the still (non-interactive) render is slow, try turning on the
delay between interactive and still rendering to avoid unnecessary
renders.
For small scale data, running the ParaView GUI in serial mode is likely
acceptable. For large scale data, interactive parallel visualization is
quite useful. For very large scale data, batch mode parallel processing
is more effective because of practical concerns like batch system queue
wait time before a parallel job is launched and system policies that
limit the size and duration of interactive jobs.
For extreme scale visualization even batch mode is beginning to be
impractical though as comparatively slow disks limit the size of data
that can be saved off by the simulation at runtime. In this domain
ParaView’s Catalyst configuration is recommended as an in situ
analysis and visualization library.
Catalyst is a visualization framework that packages either portions
or the entirety of ParaView’s parallel server framework so that it can
be linked into and called from arbitrary simulation codes. Slow IO
systems are largely bypassed via an adaptor mechanism whereby the
simulation code’s data structures are translated or ideally reused
directly by ParaView while still in RAM.
With Catalyst, full resolution simulation products stay in memory
instead of being saved to and later loaded back from disk. As the
simulation progresses, it periodically calls into ParaView. In this way
it is possible to immediately generate smaller derived data sets,
images, plots, etc. that would otherwise be generated during post
processing after a much longer, human in the loop, delay.
As explained more fully in the ParaView Catalyst User’s Guide there are
two components to making use of Catalyst. The first is to Catalyze the
simulation. This is where a software developer compiles Catalyst into
the simulation, adds a handful of (typically three) function calls to
it, and fleshes out an adaptor template with working code that produces
VTK data sets from the simulation’s own internal data structures.
Once the simulation has been Catalyzed, day to day users need to define
what ParaView should do with the data it is given. Catalyst can produce
data extracts, images, statistical quantities, etc. Any of these can be
made with Python or even lower level Fortran, C or C++ coding to
maximize runtime efficiency, but it is more flexible and convenient to
do so with recorded Catalyst scripts which are demonstrated in the next
exercise.
With Catalyst scripts the simulation input deck references a Python file
that defines the visualization pipeline. The script can do nearly
everything that ParaView batch scripts do and is generally created with
help from the ParaView GUI. To create the script one loads a
representative data set, creates a pipeline, designates the set of
inputs and outputs to and output from the pipeline, and then simply
saves out the Python file. Catalyst scripts are very similar to recorded
Python traces.
The user interface for defining the inputs and outputs is found inside
the the Catalyst Script Generator plugin. Our final exercise
demonstrates with a small example.
(Catalyst)
We demonstrate a Catalyst workflow using the ParaView
binaries and the PythonFullExample code from the ParaView source tree.
PythonFullExample is a toy simulation that uses numpy and mpi4py to
update a regular grid as time evolves. The example consists of four
files. Open and read these to begin.
The computational kernel is in fedatastructures.py. Inspection of the
code shows that it has no particular dependency on ParaView, and simply
makes up a structured grid in parallel with numpy and mpi4py.
The main loop is found in the fedriver.py. If the doCoprocessing
variable is false, this falls back to a simple loop which runs the
simulation to update the in-memory array over time. When the variable
is true the Catalyst library is exercised via three function calls:
initialize(), coprocess() and finalize().
fedriver.py and fedatastructures.py represent the simulation code. The
Catalyst parts consist of the general purpose adaptor code, found within
the coprocessor.py, and the pipeline definition, found in
cpscript.py. In coprocessor.py note in particular where the coprocess
function populates the dataDescription data structure to give
fedatastructure’s content over to ParaView. The coprocessor also takes
in, with the addscript() call, the pipeline definition file.
The starting script for this example is called cpscript.py. This simply
saves out the input it is given in a format that the ParaView GUI can
readily understand. The internals of the PipelineClass is essentially a
ParaView batch script that takes as input not a file but the
datadescription class from the adaptor.
From cpscript.py:
classPipeline:filename_6_pvti= \
coprocessor.CreateProducer(datadescription,"input")# create a new 'Parallel ImageData Writer'imageDataWriter1= \
servermanager.writers.XMLPImageDataWriter(Input=filename_6_pvti)# register the writer with coprocessor# and provide it with information such as the filename to use,# how frequently to write the data, etc.coprocessor.RegisterWriter(imageDataWriter1, \
filename="fullgrid_%t.pvti",freq=100)Slice1=Slice( \
Input=filename_6_pvti,guiName="Slice1", \
Crinkleslice=0,SliceOffsetValues=[0.0], \
Triangulatetheslice=1,SliceType="Plane")Slice1.SliceType.Offset=0.0Slice1.SliceType.Origin=[9.0,11.0,9.0]Slice1.SliceType.Normal=[1.0,0.0,0.0]# create a new 'Parallel PolyData Writer'parallelPolyDataWriter1= \
servermanager.writers.XMLPPolyDataWriter(Input=Slice1)# register the writer with coprocessor# and provide it with information such as the filename to use,# how frequently to write the data, etc.coprocessor.RegisterWriter(\
parallelPolyDataWriter1,filename='slice_%t.pvtp',freq=10)returnPipeline()
Now let us run the simulation code to produce some data.
The example will run and produce several files, among them
fullgrid_0.pvti which is a raw dump of the simulation’s full output. Let
us use that to customize Catalyst’s output.
First open the file in the ParaView GUI and inspect it. You will find
that this is a very simple structured grid with two variables, pressure
and velocity. Now insert the File → Extract Subset
filter into the pipeline to demonstrate some simple but useful
processing.
Next let’s use the Export Inspector to declare a set of files that you
want Catalyst to produce at run time. As we will see in a moment, the
ParaView GUI is able to generate Catalyst scripts by capturing the
current state of the visualization constructed in ParaView. However, the
state does not include file creation, which is typically done in
interactive sessions via File → Save Data or File
→ Save Screenshot actions.
Since ParaView 5.6, the Export Inspector is the place for defining
Catalyst’s data products. Open it by clicking Export Inspector under the
Catalyst menu. By default the panel will show up in a new tab near the
Properties Panel. Select it, if necessary, to bring it to the front.
The Data Extracts section at the top allows you to attach a writer to
the currently active element within the visualization pipeline. Make
sure ExtractSubset1 is selected in the Pipeline Browser and then choose
XMLPImageDataWriter from the file format pull down to the right of this
filter name in Data Extracts. To confirm that you want Catalyst to
perform this particular data export at run time, click on the checkbox
to the right of the file format.
If you want to change the writer’s default settings, click on the
configure button with the … label to the right of the checkbox. In the
Save Data Options dialog that pops up, you can control things like the
compression level, the frequency at which Catalyst generates files, and
the filename. The default filename is composed from the producing
filter’s name, the time step and the file format extension. Let’s change
it from “ExtractSubset1_%t.pvti” to “smallgrid_%t.pvti”. Here “%t” gets
replaced with the iteration number when the simulation runs. Later, when
we run the simulation with this script, we will get subsampled results
instead of the full grid.
To add rendered images to the simulation run, configure them with the
Image Extracts section of the Export Inspector. Just like with data
extracts, you configure outputs for the currently active view here. Do
so by making sure that “RenderView1” is active and then hit the checkbox
to enable png dumps of this view.
To save your visualization session in the form of a Catalyst script,
click Catalyst → Export Catalyst Script. Note that
all of your choices in the Export Inspector are kept with the rest of
the ParaView state, so File → Save State can make it
easy to modify your setup after the fact.
Finally quit ParaView and run the simulation again. The files produced
will now include png files for screen captures at each time step, and
vti files corresponding to the output of the Extract Subset filter at
each timestep. Simply repeat the process, adding filters and views for
example, to set up any type of data generator for the simulation.
Note this is but one interface to using Catalyst. If simulation users
are uncomfortable with ParaView and/or Python, it is entirely possible
for simulation developers to instrument the simulation code with
predefined and parameterized pipelines with or without resorting to
Python. It is also possible to create minimized Catalyst editions that
consist of just a small portion of the larger ParaView code base.
As is the case with ParaView itself, Catalyst is evolving rapidly. It
already has more advanced offshoots than described here. One, is a live
data capability in which one can connect a ParaView client to a running
Catalyzed simulation in order to check in on its progress from time to
time and do a limited amount of computational steering and debugging.
Another is Cinema, which is an image based framework for deferred
visualization of automatically generated simulation results organized in
a database. For information on these we refer the reader to the ParaView
mailing list and websites.
Thank you for participating in this tutorial. Hopefully you have learned
enough to get you started visualizing large data with ParaView. Here are
some sources for further reading.
The documentation page on ParaView’s web site contains a list of
resources available for further learning and questions:
https://www.paraview.org/documentation .
The ParaView User’s Guide is a good resource to have with ParaView. It provides
many other instructions and more detailed descriptions on many features.
The ParaView guide can be accessed from the ParaView documentation page.
If you are interested in learning more about visualization or more
specifics about the filters available in ParaView, consider picking up
the following visualization textbook: [SML06].
If you plan on customizing ParaView, the previous books and web pages
have lots of information. For more information about using VTK, the
underlying visualization library, and Qt, the GUI library, consider the
following books have more information: [KInc10], [BS08].
If you are interested about the design of parallel visualization and
other features of the VTK pipeline, there are several technical papers
available: [Mor13], [ALS+00],
[ABM+01], [CGM+06],
[ADM+07], [BGM+07].
If you are interested in the algorithms and architecture for ParaView’s
parallel rendering, there are also many technical articles on this as
well: [MWP01], [MT03], [MAF07].
Classroom Tutorials contain beginning, advanced, python and batch, and targeted tutorial lessons on how to use
ParaView, created by Sandia National Laboratories. These tutorials were created by W. Alan Scott and are
presented as a 3-hour class internally within Sandia National Laboratories.
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering
Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of
Energy’s National Nuclear Security Administration under contract DE-NA-0003525.
This tutorial will describe how to start paraview, find information and
help about paraview, and describe some of the more important controls
used by ParaView.
The ParaView web site is located at https://www.paraview.org. New
versions of paraview can be found here, along with different tutorials
and advice. ParaView versions include 32 and 64 bit versions of Linux,
Windows and Mac OS X. Training (practice) data is included in all ParaView
downloads, and can be accessed through File → Open → Examples.
Did you know?
paraview now has an integrated help. It is found under the menu item Help → Help.
The Startup Screen includes two important links. Both of these
links can also be found from the Help menu. They are the Getting
Started Guide and Example Visualizations.
can.ex2 is one of the datasets included with ParaView in the
Examples folder.
In paraview, File → Open.
In the upper left corner, there is a folder called Examples. Go into this folder.
Select can.ex2.
OK.
Under the Properties tab, all Block Arrays will be selected.
Apply.
Turn off the node variables for ACCL. Since any variable that is
selected takes up memory, and since some datasets are huge, often the
user will only read in the data that is needed for a run.
Click ACCL, turning the check box OFF.
Apply.
The screen should now look like this. (The square will show up as
red, since ParaView defaults to coloring by block, and the block we
are seeing is red.) You are looking at the bottom of the plate that
the can is sitting on.
Lets move the 3d object. Grab the can using the left mouse
button. Try the center button. Try again with the right
button. Try all three again holding down the SHIFT key. Try again
holding down the X, Y and Z keys.
Place your mouse on a corner of the can. Now, hold the CTRL key down,
and move the mouse up and down. You can zoom into and out of that
location.
Now the screen looks like this:
Notice that the can dataset is being painted in two colors -
To change the representation, change Surface to Wireframe
(right below Help).
Then, change it to Surface with Edges.
Finally, turn it back to Surface.
Change the variable used for color. Change this from Solid Color
to Displacement (Point DISPL). (This is found just below the
Sources menu.) Everything should go blue.
Animate the can one frame. Right above the window of the can are
animation controls. Click the right arrow with a bar to its left
once. The plate turns red.
Did you know?
The can dataset has displacement information in
it. We are actually running the plate into the can, and the whole
object is moving.
Notice that our color map is not set correctly. It needs to be set over the whole range of
displacement, so that it grades from blue to red.
Be careful!
Very, very large data can take a long time to
process. Don’t animate your data unless you have to with very
large datasets.
Click the single right arrow, running to the end of the simulation.
Click the Rescale to Data Range button.
Rewind using the animation control furthest left arrow, then click
the single right arrow again.
Drag the can around with the left mouse button until you can see the can.
Select Filters → Common → Clip (Notice that
this is also the third icon from the top on the far left of the
screen.)
Apply.
Press X Normal.
Apply.
Try also Y Normal.
Apply.
Grab the arrow control at the end of the clip object with the left
mouse button. Drag it around. You can also grab the red box and slide
the clip plane forward and backward.
Apply.
Turn off the Show Plane checkbox.
Select Inside Out.
If the clip arrow control is ever hidden behind data, you can see it
by clicking on the “eye” to the left of the “clip” in the Pipeline
Browser which is located in upper left corner of the screen.
Drag the can around with the left mouse button until you can see the can.
Select Filters → Common → Slice.
Apply.
Press Y Normal.
Apply.
Try also Z Normal.
Apply.
Grab the arrow control at the end of the clip object with the left
mouse button. Drag it around.
Apply.
Turn off the Show Plane checkbox.
We need to go to the Advanced Properties tab. Click on the little
gear to the right of the search box.
In the Slice Offset Value section, press New Value, type
1. Apply. Notice that we just added a second cut plane.
Under Slice Offset Values, press Delete All. Select New
Range. Input From value of -4 and To value of 4. OK.
Apply. Now we have 10 slices through our object.
Play the animation.
If the slice arrow control is ever hidden behind data, you can see it
by clicking on the “eye” to the left of the “clip” in the Pipeline
Browser which is located in upper left corner of the screen.
Press the Threshold button , found to the far left. (Notice that
you can also find this through the filters menu.)
Select Scalars “Temp” (Temperature).
Note: The blue recycle button will set the min and max values.
Change the Lower Threshold to 400.
Apply.
Set Coloring to Pres.
Spin the object around, and look at it.
Now, let’s place this hot section back into the cylinder.
Let’s open another version of disk_out_ref.ex2, using the File → Open menu.
Apply.
Make sure that the second disk_out_ref.ex2 is highlighted in the
Pipeline Browser
Set Representation to Wireframe.
In the Properties tab, set Coloring to Pres
What we have done: We have created an unstructured grid holding
the cells that fit our criteria. This can make our data much bigger,
and should be avoided if we are working with big data.
Extra credit:
Change the outside cylinder to be volume rendered, set Representation to Volume.
This represents the location inside of the cylinder that is at
temperature 400, and is colored by pressure.
Turn the visibility back on for the disk_out_ref.ex2.
In the Pipeline Browser, click disk_out_ref.ex2 (turning it white)
Select Representation Wireframe.
Set Coloring to Pres.
Notice that this is another way to see two representations of the
same object by reading the object in once and modifying it. In the
Threshold Filter (above), we read in the object twice, and displayed
each object differently.
What we have done: We have created an isosurface of a specific
temperature. One nice thing about isosurfaces is that they decrease
the amount of data that has to fit into memory. This is handy when
you are displaying big data.
Extra credit:
Highlight disk_out_ref.ex2.
Select Clip filter.
Select X Normal for the clip plane.
- Why has the disk_out_ref.ex2 model now turned solid? (Hint – the visibility has changed)
More extra credit:
Under contour, Advanced Properties tab, delete the Isosurface, and use New Range to create 10 new surfaces.
Again, the Advanced Properties tab is enabled by clicking on
the gear icon to the right of the search box.
Next, select Clip filter to cut the cylinder in half.
What are the surfaces showing us? What are the colors showing us?
These filters are used to convert a data set from having cell data to
having point data and vice versa. This is sometimes useful if a filter
requires one type of data, and a user only has the other type of data.
An example would be using can.ex2. You cannot get a contour of EQPS
directly, since EQPS is cell data and contour only works on points. Use
the filter Cell Data to Point Data first, then call contour.
In the empty line below, type cos(GlobalElementId)*sin(GlobalElementId).
Did you know?
You can pull in the names of the variables by clicking on the Scalars/Vectors button.
In the Properties tab, set Coloring to RandomNumber.
We are now coloring by a pseudo random number. This shows how complex our data is.
Note that you can create a vector from three scalars using the
calculator. For instance, to create an X,Y,0 vector from Velocity,
type VEL_X*iHat+VEL_Y*jHat+0*kHat.
To get the length of a vector, use mag(vector_name).
To get the length of a vector squared, use mag(vector_name)*mag(vector_name).
paraview allows users to customize settings. The most important ones are
found in Edit → Settings → General. These are:
Auto Apply - Also found as an icon below the Macros menu.
Auto Convert Properties - Automatically call Cell to Point,
Point to Cell, or extract components from vectors as needed.
Transfer Function Reset Mode - when to update the minimum and
maximum for the Color Legend.
Grow and update on Apply - default. This means only update
when told to.
Grow and update every timestep. This means to update the
Minimum and/or Maximum only if the current timestep exceeds
these numbers. Basically, Add and grow.
Clamp and update every timestep. Set the minimum and
maximum every timestep, from the data this timestep. This is
not recommended behavior, since it makes comparing frame to
frame confusing.
The first section is the File Properties of the dataset.
The second section is Data Grouping, which tells you what blocks and sets you have in this dataset.
The third section is Data Statistics which tells you:
The number of cells
The number of points
The amount of memory used
The bounds which give the X, Y and Z bounds of the bounding box.
The fourth section is Data Arrays which gives information on each variable, including the min
and max. Note that this is for the current timestep only.
The last section is Time which gives a list of all timesteps, with their associated time.
Next, Using the left mouse button, grab the title bar of the lower
left window and drag/drop it into the upper window. These two windows
have now switched places.
Finally, grab the divider between the two lower windows and drag it
left and right. You can also move the divider between the upper and
lower windows.
The Properties tab has three buttons on top: 1) Apply
button, 2) the Reset button and 3) the Delete button. The Reset
button will undo any Properties tab changes that a user accidentally has
made. Below these three buttons is a search feature. Search will find
Properties tab items, irrespective of them being standard or advanced.
An example would be Opacity.
The properties tab initially is in standard layout. To get to the
advance layout, click the gear icon. Advanced reader or filter properties
are found here. The advanced layout icon is .
ParaView allows the user to change and store the position of the camera.
Such controls as Roll, Elevation and Azimuth are available.
The Adjust Camera icon is on the left side of the row
of icons at the top left of the 3d window.
The Adjust Camera dialog box looks like this:
Useful controls that I often use (in order) are as follows:
Custom Configure - Save up to 4 camera positions.
Azimuth - rotate around the vertical axis. Be sure to hit the
button after entering a number.
Elevation - rotate around the horizontal axis in the plane of the
screen.
Roll - rotate around the axis coming out of the screen.
View angle - basically a zoom in.
Camera position - where the camera is.
Focal point - where the camera is looking.
You can always recenter the object using the Reset icon. First,
however, be sure to change View angle back to 30.
It is possible to change the specular highlights in ParaView. This is on
the Properties tab, about half way down. It is called Lighting:
Specular. Note that reflections can look like the center of the color
map, thus specular highlights are turned off by default.
ParaView allows users to easily control the color palette. This is done
with the Load a color palette icon. . Changing
color palettes does much more than just changing the background - it
also changes the font colors for other annotations. Options are default
gray, black, white and gradient. You can also create custom color
palettes.
Here is an example of a gradient background, with the color palette menu
displayed.
A famous example of surrounding colors changing a perceived brightness
of an object is Edward Adelson’s Checker Shadow illusion.
The checker shadow illusion: the square A is exactly the same shade of grey as square B. Copyright
Edward H. Adelson and
Pbrks :
CC BY-SA 4.0.
The checker shadow illusion: drawing a connecting bar between the two squares breaks the illusion and
shows that they are the same shade. Copyright Edward H. Adelson and
Adrian Pingstone : Copyrighted free use.
Move forward one time step using the Next Frame icon.
Here is the coloring toolbar. Icons are as follows:
Toggle color legend visibility.
Edit color map.
Rescale to data range (set Min and Max from this timestep).
Rescale to custom data range (manually input Min and Max values.
Rescale to visible data range (set Min and Max from visible
objects this timestep)
Click on the Edit Color Map icon.
The Color Scale Editor is used to change the colormap.
Select the Use log scaling when mapping data to colors check
box. Notice what has happened to the colors on the can.
Unselect Use log scaling when mapping data to colors check box.
Select the Enable opacity mapping for surfaces check box.
Notice what has happened to the colors on the can.
Unselect Enable opacity mapping mapping for surfaces check box.
Select the Rescale to Data Range icon. You already know what this does.
Select the Rescale to Custom Range icon.
Set custom minimum and maximum values for the Color Legend.
Select the Rescale to Data Range over all timesteps icon. This
will read in all of your data, and set the min and max based upon
all timesteps.
Select the Rescale to Visible Range icon. Rescales based upon
what is currently visible. To see this work, click -Z, and then
roll the can down slightly to hide the can itself. Click the
Rescale to Visible Range icon.
Invert the transfer function.
Invert the color table.
Select the Choose Preset icon.
Choose Cool to Warm
OK. Notice what has happened to the colormap. This is an easier to
understand color map than the rainbow one that all of us are used
to.
Next, choose the Black-Body Radiation preset. Although
harder to understand (requiring an understanding of the layout of
the rainbow colors), this one makes prettier pictures. The best
color map to use is the default one.
Advanced. You can edit each color and opacity of the color map.
Nan Color - this is the color ParaView will use to paint nans in
your data.
Click the advanced icon at the top. You can mark cells or points
that are outside of the normal range of the color map.
Click the color legend with the e. This is the Color Legend
Editor.
ParaView allows you to import custom color maps. This is also done on
the Color Map Editor, Presets dialog. An excellent source for
scientific visualization color maps is the SciVizColor website, located
here: https://sciviscolor.org. Lets add a custom color map.
This use case shows a user how to plot cell and point data. Plotting can
be along a line that cuts through your data, or a location with respect
to time.
Drag the can around with the left mouse button until you can see the can.
Select Filter → Data Analysis → Plot Over Line.
Drag the top of the line to intersect the top of the can. Note that hitting
the p key will also place the line on the surface of your object. You can also
use the 1 and 2 keys to set the beginning and end of the line.
Apply.
In the Properties tab, unselect all variables except DISPL (Magnitude).
Lower on the Properties tab, select Left Axis Use Custom Range, and
enter 0.0 and 20.0.
Select Bottom Axis Use Custom Range, and enter 0.0 and 20.0.
Play the animation forward, and notice what happens to the plot.
You can also add plot labels and axis labels on the properties tab.
Save only selected view will save either the whole window, or the
selected view.
Change the size of the output files. Note that paraview can save
files that are significantly larger than the current view. This is
done in off screen memory.
Leave image quality as is.
Override Color Palette allows a user to change the background
color - for instance, to white.
Stereo mode allows a user to save stereo images.
OK
Save your images as .png or .jpg. .png is a cleaner format, but
.jpg’s may be smaller.
Name and save the file. OK
In PowerPoint:
Add a new slide.
Next, click Insert → Picture→ From File…, and pick up the file that we saved in the previous paragraph.
You can move the file anywhere you want by holding the left mouse button and dragging.
You can resize the picture by grabbing one of the corners and dragging the picture smaller.
Change the size of the output files. Note that paraview can save
files that are significantly larger than the current view. This is
done in off screen memory.
Set timestep range.
Stereo mode allows a user to save stereo images.
OK
Save your movie. A great option is to save your images as .png or
.jpg, and then post process them into .avi or .mov files. This
way, you have your movies and the individual frames. .png is a
cleaner format, but .jpg’s may be smaller.
Name and save the file.
OK
In PowerPoint:
Add a new slide.
Next, click Insert → Movies and Sounds → Movie from File.
Browse to the location of your movie.
Select your file.
OK.
Decide if you want the slide show to be Automatic, or when clicked.
Finally, remember that this file is NOT inserted into the PowerPoint slide.
You will want this file to be on the computer – in the same location – as it was when you selected it.
A few notes on file formats for movies. You can make .avi files directly
on Windows, Linux or Mac. If you are trying to make movies on Linux or
Mac, or are making movies for a powerwall, use format .png or .jpg.
Then, if you want .avi files for use with PowerPoint, convert these
movies to .avi format as needed. One option is to use enve, which is
available when downloading EnSight. Windows reads .avi files well, both
using and not using PowerPoint. Linux is able to display either format
if the correct video player is installed. One option is VLC. VLC
is installed from .rpm files, which can be found on the net.
bake.e is a dataset that simulates the heating of a cone in a test
facility. It has numerous blocks. T (for temperature) is the primary
variable of interest.
Open the dataset bake.e.
Apply.
Your dataset is now colored by block.
Change vtkBlockColors to T.
Your dataset is now colored by temperature.
Play forward in time, and look into the simulation.
Be sure to rescale to data range.
Change color back to vtkBlockColors.
Notice that this model has 6 sides, and there are 12 annotation colors.
Thus, they repeat. Lets make them random.
In the Properties tab, click Advanced.
Slide down towards the bottom, and find Block Colors Distinct Values, and change it to 11.
Right click on a side (a block). Notice that the bock name and ID are shown.
Right click on a side. Change the block’s color and opacity.
Right click on a side. Hide, then un-hide the block.
Two filters that can also be used to partition your data are the Extract
Block and Extract Selection filters. Instead of reading your data in
twice, read it in once and Extract Block twice.
Control label display on your data in the 3d view.
Shortcut to run data analysis filters.
We will explore this panel using an example.
Open a dataset and the Find Data panel.
Open can.ex2.
Apply.
Edit → Find Data. You can also open the Find Data panel
using the icon
We will select an ID.
Set Data Producer to can.ex2.
Set Element Type to Cells.
Change pulldown to ID. Leave as is. Enter 100.
Only select block_1
Find Data
We will select two IDs.
Find Cells from can.ex2
Change pulldown to ID. Change to is one of. Enter 100, 102.
Find Data
We will select the maximum EQPS.
Move forward one timestep. EQPS for timestep 0 is all the same - 0.
Set Data Producer to can.ex2.
Set Element Type to Cells**.
Change pulldown to EQPS. Change to is max.
Find Data
Play forward
Notice that the data for the selected cell (or point) is displayed in
the spreadsheet.
If desired, the maximum (or minimum) cell can be found, and this
selection can be frozen. The same cell will then be selected for all
timesteps. Use the Freeze Selection button to freeze selections.
We can also display cell or point data on the 3d view. This is done with
Cell Labels and Point Labels.
paraview has a very powerful group of selection tools. Selections are
found as a group of icons in the upper left corner of the 3d view.
More than one selection can be active at a time. Use the CTRL key.
You can also use the Add Selection, Subtract Selection and
Toggle Selection icons.
Variable data can be printed on the screen for any cell that is
selected. See the section on Find Data.
Selections can be used as input to numerous Data Analysis
filters.
Select Cells On. Select one or more cells on the surface of
your object. Either a single click or rubber band select works. Shortcut -
s.
Select Points On. Select one or more points on the surface of
your object. Either a single click or rubber band select works. Within a
tolerance, the nearest point will be selected. Shortcut - d.
Select Cells Through. Select cells through your dataset. This
is known as a Frustum select. Shortcut - f.
Select Points Through. Select points through your dataset.
This is also known as a Frustum select. Shortcut - g.
Select Cells With Polygon. Select cells on the surface of your
dataset by drawing a polygon. No shortcut.
Select Points With Polygon. Select points on the surface of
your dataset by drawing a polygon. No shortcut.
Select Block. Select one or more blocks. Either click or
rubber band select works. Shortcut - b.
Interactive Select Cell Data On. If your dataset is colored by a
cell data array of type idtype, interactively select all cells
in that dataset with the same value as the cell under the
cursor. No shortcut.
Interactive Select Point Data On. If your dataset is colored by a
point data array of type idtype, interactively select all points
in that dataset with the same value as the point under the
cursor. No shortcut.
Interactive Select Cells On. Interactively select cells on the
surface of your dataset. If you click on a selection, it will
become permanent. You can have numerous permanent selections. No
shortcut.
Interactive Select Points On. Interactively select points on
the surface of your dataset. If you click on a selection, it will
become permanent. You can have numerous permanent selections. No
shortcut.
Hover Cells On. This will display all of the data available
on this cell. Interactive.
Hover Points On. This will display all of the data available
on this point . Interactive.
Grow Selection. This will grow selection to include any cell
touching a previously selected cell.
Shrink Selection. This will remove the selection of any cell
touching an unselected cell.
paraview can visualize data in a spreadsheet view. The spreadsheet view
can be configured to show all data, or only selected data. You can also
select a row in the spreadsheet view and it will be selected in the 3d
view.
You can also show your data as a histogram. This will show you how many
cells have different attributes.
Open can.ex2.
Apply.
Highlight the can window, and Select Cells On on the can.
Split Horizontal.
Split Vertical.
In the upper right window, select Spreadsheet View.
Select the Show Only Selected Elements check box (next to
Precision).
Note that the Spreadsheet can now be sorted - including in
parallel.
Select a different cell on the can.
Highlight the lower right window.
We want magnitude of the DISPL vector.
Select Filters → Common → Calculator.
Set Expression to mag(DISPL). Result Array Name → MagDispl.
Apply.
Filters → Data Analysis → Histogram.
Apply.
Close the 3d RenderView
Change Select Input Array to MagDispl.
Apply.
Animate forward in time one step at a time.
Play.
If desired, freeze the X and Y axis in the Properties tab using
Axis Use Custom Range.
You can either display all of your dataset’s points or cells in your
spreadsheet, or only those that are selected in the 3d view. With the
spreadsheet window selected, in the Properties tab, click Show
only selected elements.
When cells or points are selected in the 3d RenderView, the appropriate
row(s) in the spreadsheet view will be highlighted.
Highlighting works both ways - if you select a row or rows in the
spreadsheet view, the cell or point on your dataset will be selected.
You can select multiple rows in the spreadsheet by holding down the
CTRL key, and can select ranges of rows by holding down the SHIFT key.
In the Animation View window, change the mode to Real Time, and the
Duration to 100.
Play. Notice that the can motion is now very slow. We are saying that
we want the whole animation to last 100 seconds.
Note: This can also be used to speed up datasets with a large number
of time steps. Set the Duration to 10, and paraview will animate over
all time in 10 seconds. Obviously, this depends on the whether
paraview can keep up with this frame rate!
In the Animation View window, change the mode to Sequence, and the Nunber of Frames to 200.
Filters → Temporal → Temporal Interpolator.
Play. Notice that the can motion is now smooth. paraview is
interpolating between frames, and making 200 time steps.
Note that this only works with data that has a constant mesh through
the whole time sequence. AMR (Adaptive Mesh Refinement) data does
not work with the Temporal Interpolator.
Add a camera. Change Orbit to Follow Data. Click the blue +.
Play.
Did you know?
The follow data option will follow the data from whatever filter is highlighted.
This means that you can choose one cell, run the Extract Selection filter,
and follow this cell. Note that you must keep visibility on for this cell. If
needed, you can turn the cell’s Opacity in the Properties tab to 1%, making
it disappear. By turning visibility on for your whole dataset, you can follow
the cell but display all of your data.
We are going to move the camera along a straight line. We want to move
the camera to follow the can.
Edit → Reset Session.
Open can.ex2.
Apply.
+Y.
View → Animation View.
Add a camera. Change Orbit to Interpolate Camera Position.
Click the blue +.
Left click on the white section of the camera row that just appeared.
An Animation Keyframes dialog will open.
Left click the top Position.
Use Current.
OK
Play to the last timestep.
Move the can dataset back into the center of the screen. Tip - Don’t hit Reset.
Left click the bottom Position.
Use Current.
OK.
OK.
Play.
You can also create an intermediate destination for the can by going to
the Animation Keyframes dialog, and selecting New. Then, follow the
directions above. Experiment by adding more keyframes and different
camera angles.
A way to create tracks in 3d space for use with Interpolate Camera
Location is to create the points external to Interpolate Camera Location,
and then copy them into place. One way to create these external points is
to use a Sources/ Plane. Orient the plane in the 2d plane you want the
camera to track. Now, create a Spline source. Create additional control
points, and selecting each control point, use the p key to place them
on the plane. Copy these points into the Interpolate Camera Location
controls.
In the previous example we showed how to manipulate the camera using the
Animation View tools. In this example we will show how to animate a
filter. Our goal is to move a slice through our dataset over time.
Lets start from scratch. One way is to go Edit → Reset Session.
Ok.
If you closed it, bring up the Animation View.
Open disk_out_ref.ex2.
Apply.
Select Slice filter.
Apply.
Turn off the Show Plane.
In the Animation View, change Mode to Sequence, and number of
frames to 400.
We want to create a Slice track.
Slice Offset Values.
Click the blue +.
Double click on the track. This will bring up a dialog, and will set
the start and end.
Change the starting value to -8 and the ending value to 8.
In this example we will show how to animate your data set. Our goal is
to show one data set, then fade into another dataset. This can be handy
when one physics simulation runs for an early time period, and another
physics simulation runs for the later time period.
Lets start from scratch. One way is to go Edit → Reset Session.
OK.
If you closed it, bring up the Animation View.
Open can.ex2.
Apply.
Open can.ex2 again.
Apply.
Select the upper can.ex2.
Set Coloring to DISPL.
Go the last time step.
Rescale to Data Range.
Go to first time step.
Select the lower can.ex2.
Change the representation to Wireframe.
We now want to fade from the first version of the can to the second
version of the can. This is done as follows:
On the Animation View, on the can.ex2 pulldown menu, select the upper
can.ex2.
Right of there, use the pulldown menu to select Opacity.
Click the blue +.
Do the same for the lower can.ex2.
Click on the upper can.ex2 white horizontal bar.
Double click on the upper value, change it to 1.
Double click the lower value, change it to 0.
OK.
Play.
You can substitute Visibility for Opacity when you add tracks to the
Animation View. Then, on one dataset, you can run visibility of 1 for
half of your time, and run visibility of 1 for the other dataset for the
second half of your time. Thus, you will show the first simulation for
the first half of your animation, and the second simulation for the
second half.
If your dataset has displacement data, but it is not using a variable
name that ParaView recognizes, you can still animate your data.
Choose the Filters → Alphabetical → Warp Vector filter.
ParaView state files are saved by selecting the menu option File → Save State.
These files can be saved as .pvsm files (xml) or .py files (python).
The pipeline, orientation of the data set, and all view windows are saved.
Select File → Load State to open a saved ParaView state file.
This feature will save the data output from the selected source/filter.
The Save Data feature is selected from the main menu: File → Save Data.
The data type is whatever you chose when you save the data. If a data
type is missing, it probably means you are trying to output data that is
not supported by this dataset format. For example, you need to have
surface data, as triangles, to output .stl files.
Save Data can be used to:
Create .csv files of your data which can be read into spreadsheets and other programs.
Create .stl files. which are often used for additive manufacturing, or animation programs.
Run filters Extract Surface then Triangulate before saving Data.
Create files Houdini can ingest. These are .geo files.
Again, run filters Extract Surface then Triangulate before saving Data.
This feature will save whatever is in the viewport to a file. The Export
Scene feature is selected from the main menu: File → Export Scene.
Again, the data type is whatever you chose when you export scene.
Export Scene can be used to:
Create .webgl files of what is displayed in the viewport.
A .html file will be written out, which you can load in a web browser.
This format allows users to create interactive data products that anyone can load in a web browser.
Create .pdf files of what is displayed in the viewport.
paraview can now automatically save traces, or macros. This means that
you can start recording a trace, do something, stop recording a trace,
and save this trace into a file. You can then use this trace file as
input to the pvbatch program, or as a macro within paraview.
Example:
Tools → Python Shell → Trace → Start Trace.
Open disk_out_ref.ex2.
Apply.
Select Clip.
Use Z normal.
Unselect Show plane.
Apply.
Select Slice.
Unselect Show plane.
Apply.
Set Coloring to Temp.
In the Python Shell window, Stop Trace.
Save trace.
Save as macro.
Call it Super-disk.
Close the editor.
Now, lets run the trace.
On the Macros toolbar, you will see Super-disk. Click it.
Build the vector equation using the iHat, jHat and kHat buttons on
the calculator. For instance, this example will create a vector
representing the acceleration in the X and Y plane.
It is possible to change the backface style of a wire frame object.
- Open can.ex2.
- Apply.
- Set Coloring to ids.
- Set Representation → Wireframe.
- In the Properties tab, Click Advanced.
- Slide down a few pages until you find Backface Styling.
- Set Backface Representation → Cull Backface.
If you have a vector field in your data, you can animate a static
dataset.
Our goal is to create a set of streamlines from a vector field, place
points on this set of streamlines, and animate the point down the
streamlines. We will also add glyphs to the streamline points.
Open disk_out_ref.ex2.
Apply.
Click -X.
Select Filters → Common → Stream tracer. (We are already streamtracing on V).
Set Seed Type to Point Cloud.
Unckeck Show sphere.
Set Opacity to 0.3.
Apply.
Open View → Color Map Editor.
Click Invert the transfer functions.
Select Filters → Common → Contour.
Contour on IntegrationTime.
Apply.
Select Filters → Common → Glyph.
Set Orientation Array to v.
Set Glyph Mode to All Points.
Set Scale factor to 0.5.
Set Coloring to v.
Apply.
In the Pipeline browser, hide Contour1, and show SteamTracer1 and Contour1.
View → Animation View.
Set Mode to Sequence.
Set No. Frames to 100.
Change the pulldown box next to the blue + to be Contour1.
ParaView offers a rich and powerful Python interface. This allows users
to automate processing of their data, and gives access to powerful tools
in the Visualization Tool Kit (VTK). This tutorial will describe
ParaView and Python. It shows a user how to drive ParaView using Python
commands, and how to automate the creation and use of these commands.
ParaView has a client / server architecture. The client includes the
ParaView GUI and display. The server reads the user’s data, processes
the data, and passes these images to the client. We can use Python to
control ParaView either in the GUI, at the client level, or directly on
the server.
We want to color by the variable. Be sure to Show the Clip, and not the Can.
Steps are, move forward one timestep, get the renderview, get the
display, get the variables, ColorBy.
We want to create a script that allows us to scale a dataset around it’s center.
This example shows how to get the active source, get the bounds, and transform the camera.
paraview includes a tool to automatically generate Python scripts for
us. It is called the Trace Recorder. An example is as follows.
Read in can.ex2, clip can, paint by EQPS, change the camera to +Y,
write out a screenshot and write out a movie. The steps are:
Tools → Start Trace Select Show Incremental Trace.
Open can.ex2.
OK.
Turn all variables on.
Apply.
+Y.
Select Clip.
Y Normal.
Unselect Show Plane.
Apply.
Set Coloring to EQPS.
Last timestep.
Rescale to Data Range.
Set First timestep.
File → Save Screenshot. Save as .png.
File → Save Animation. Save as .avi.
Tools → Stop Trace
File → Save to a known location.
Another way to find Python for paraview is through Save State. This
should be a last resort, but it may include commands that the Trace
Recorder missed. ‘’’File → Save State → Python State File.
paraview can save and use Python scripts that have been placed in a
known location. When you create a trace, you have the option to File →
Save As Macro. You also have the option on the Macros menu to Add
new macro. Macros will be added to the Macro toolbar at the top of the
ParaView GUI. You can edit and delete these Macros through the Macro
menu.
As an example, lets add the python script that we created above.
Macros → Add new macro, find your macro, and click OK.
ParaView has three filters that give a user access to python math
functions as well as the underlying VTK library. These are the Python
Calculator, the Programmable Source and Filter. This tutorial explains both.
The Python Calculator allows a user to apply calculations that are
available in Python. These include such functions as get volume of
cells, get area of cells, get the cross product, dot product, curl, etc.
The whole formula must fit on one line. Lets go over the Python
Calculator with an example.
Lets create a new point variable, loaded with 5.
Open can.ex2.
Turn all variables on.
Apply.
Filters → Alphabetical → Python Calculator.
Change Expression to 5.
Set Array Association to Point Data
Change Array Name to Calculated Variable.
Apply.
Paint by Calculated Variable.
Lets create a variable equal to two times displacement.
Change Expression to DISPL*2.
Apply.
Go to last timestep.
Rescale to Data Range.
Note: A more complete way to access displacement data. We explicitly pull
DISPL from the first input to the filter. Don’t forget that the first
input is [0], the second is [1], etc.
Change Expression to (inputs[0].PointData[‘DISPL’]) * 2.
Apply.
Rescale to Data Range.
Here is how to multiply a vector by a global variable. Lets multiply
DISPL by the timestep (TMSTEP)
Change expression to inputs[0].FieldData[‘NSTEPS’][time_index] * DISPL.
Apply.
Rescale to Data Range.
To recap, If a function requires a variable input, use the string above. If the
function needs the input mesh, use inputs[].
Did you know?
Python uses square brackets for arrays, and parenthesis
to group parts of your formula. Also, to designate a string (i.e.,
variable name), use either single or double quotation marks.
Lets create a variable to contains the cell volume.
Change expression to volume(inputs[0]).
Apply.
Rescale to Data Range.
Numerous functions can be combined in one expression. For instance, a
nonsensical expression would be to take a sin of a divergence of a
curl. Here is the expression:
Change expression to sin(divergence(curl(‘ACCL’))). Apply.
Rescale to Data Range.
Interesting are functions available through the Python Calculator:
area(dataset)
aspect(dataset)
cos(array)
cross(X,Y) where X and Y are two 3D vector arrays
curl(array)
divergence(array)
dot(a1,a2)
eigenvalue and eigenvector(array)
gradient(array)
max(array)
mean(array)
min(array)
norm(array)
sin(array)
strain(array)
volume(array)
vorticity(array)
The complete list can be found in Section 5.9.3 of the User’s Guide.
The Programmable Source is used to either be a source for new data, or
to read in data from a file. It is written in Python. Later, filters
will be used to modify this data. An example of a Programmable Source
would be reading a .csv file into paraview.
Create a .csv file named data.csv. Place the following into this
file.
x coord, y coord, z coord, scalar
0,0,0,0
1,0,0,1
0,1,0,2
1,1,0,2
-0.5,-0.5,1,4
-0.5,-0.5,1,5
-0.5,-0.5,1,6
-0.5,-0.5,1,7
Set the timestep to the one whose displacement you want to be zero.
The output of this filter is the can.ex2 dataset “frozen” at the chosen timestep. It will not change as
you advance through time.
Select both can.ex2 (using the CTRL key) and the ForceTime1 sources in
the Pipeline Browser. Note that the original can.ex2 source will
update as the timestep changes, but the ForceTime1 source will not change.
Substract the displacement in the “frozen” data set from the current timestep in can.ex2.
Set the expression to inputs[0].PointData[‘DISPL’] - inputs[1].PointData[‘DISPL’]
The order of inputs into the Python Calculator is not well
defined, so you may need to swap the indices in inputs[0] and
inputs[1] to get the correct sign on the result, but this should work.
(If desired,) Finally, add a Plot Selection over Time filter. This
filter will run over all time steps, subtracting the data from the
current timestep from the data in the “frozen” timestep produced by the Force Time
filter, and plot the result in a graph. The first timestep should have a value of 0.
Read eigenvector, calculate an eigenvalue, and place it into three variables
# ParaView Programmable Filter script. ParaView 5.0.1.## This code will read in an eigenvector, calculate an# eigenvalue, and place it into three variables.## Be sure to correct the input variables below. Also, note that# the code uses ZX, not XZ.## This code only works with any multiblock or vtk# datasets (including ones with only one block - i.e.,# Exodus datasets as input).## Usage: Run the Programmable Filter.# Cut and paste this file in the section named "Script".# Leave "Output Data Set Type" as "Same as Input".# Click Apply button## Written by Jeff Mauldin and Alan Scott#importnumpyasnpdefprocess_composite_dataset(input0):# Pick up input arraysxxar=input0.CellData["EPSXX"]xyar=input0.CellData["EPSXY"]zxar=input0.CellData["EPSZX"]yyar=input0.CellData["EPSYY"]yzar=input0.CellData["EPSYZ"]zzar=input0.CellData["EPSZZ"]#print `xxar`#print len(xxar.Arrays)# Set output arrays to same type as input array.# Do a multiply to make sure we don't just have a# pointer to the original.outarray0=xxar*0.5outarray1=xxar*0.5outarray2=xxar*0.5# Run a for loop over all blocksnumsubarrays=len(xxar.Arrays)foriiinrange(0,numsubarrays):# pick up input arrays for each block.xxarsub=xxar.Arrays[ii]xyarsub=xyar.Arrays[ii]zxarsub=zxar.Arrays[ii]yyarsub=yyar.Arrays[ii]yzarsub=yzar.Arrays[ii]zzarsub=zzar.Arrays[ii]#print `xxarsub`# Transpose and calculate the principle strain.strain=np.transpose(np.array([[xxarsub,xyarsub,zxarsub],[xyarsub,yyarsub,yzarsub],[zxarsub,yzarsub,zzarsub]]),(2,0,1))principal_strain=np.linalg.eigvalsh(strain)# Move principle strain to temp output arrays for this blockoutarray0.Arrays[ii]=principal_strain[:,0]outarray1.Arrays[ii]=principal_strain[:,1]outarray2.Arrays[ii]=principal_strain[:,2]#ps0 = principal_strain[:,0]#print "ps0 len: " + str(len(ps0))# Finally, move the temp arrays to output arraysoutput.CellData.append(outarray0,"principal_strain_0")output.CellData.append(outarray1,"principal_strain_1")output.CellData.append(outarray2,"principal_strain_2")defprocess_unstructured_dataset(input0):# Pick up input arraysxxar=input0.CellData["EPSXX"]xyar=input0.CellData["EPSXY"]zxar=input0.CellData["EPSZX"]yyar=input0.CellData["EPSYY"]yzar=input0.CellData["EPSYZ"]zzar=input0.CellData["EPSZZ"]#print `xxar`#print len(xxar.Arrays)# Transpose and calculate the principle strain.strain=np.transpose(np.array([[xxar,xyar,zxar],[xyar,yyar,yzar],[zxar,yzar,zzar]]),(2,0,1))principal_strain=np.linalg.eigvalsh(strain)#ps0 = principal_strain[:,0]#print "ps0 len: " + str(len(ps0))# Finally, move the temp arrays to output arraysoutput.CellData.append(principal_strain[:,0],"principal_strain_0")output.CellData.append(principal_strain[:,1],"principal_strain_1")output.CellData.append(principal_strain[:,2],"principal_strain_2")input0=inputs[0]ifinput0.IsA("vtkCompositeDataSet"):process_composite_dataset(input0)elifinput0.IsA("vtkUnstructuredGrid"):process_unstructured_dataset(input0)else:print"Bad dataset type for this script"
Important note: Since the Programmable Source and Programmable Filter work at the
server level, paraview.simple cannot be loaded or used.
Mode details about the Programmable Filter can be found in Section 5 of the
Reference Manual.
Additionally, this is list of interesting Blog Posts related to the Programmable Filter:
pvpython is the Python interface to ParaView. You can think of pvpython
as ParaView with a Python interface. As we did with the Python Shell,
you can manually type in commands to pvpython. The first thing you will
want to do is import paraview simple, as follows:
fromparaview.simpleimport*
pvpython can also read Python command files. Type pvpython –help for
arguments. Running pvpython files looks like this:
/pathTopvpython/pvpython /pathToPythonCommandFile/commandFile.py# Example
D:/alan/paraview/pvpython D:/alan/scripts/disk_out_ref-A.py
You will notice that pvpython will run the script and then exit. The
output of the script is a screenshot or other data product.
Anywhere that needs editing in the scripts above will be marked by the string editMeHere.
You will need to hard code in the paths to your data, and paths for output products.
The first time you run a script with pvpython, the output will be a
postage stamp sized window. You can change this by finding and
uncommenting the line renderView1.ViewSize.
Try making and running a script of your own. Alternatively, here is
an example. Cut and paste the following into a file named
greenSphere.py:
#!/usr/bin/env pvpythonfromparaview.simpleimport# Lets create a spheresphere=Sphere()Show()Render()# get active viewrenderView1=GetActiveViewOrCreate('RenderView')renderView1.ViewSize=[1670,1091]# get display propertiessphere1Display=GetDisplayProperties(sphere,view=renderView1)# change solid colorsphere1Display.AmbientColor=[0.0,1.0,0.0]sphere1Display.DiffuseColor=[0.0,1.0,0.0]# save screenshotSaveScreenshot('greenSphereScreenshot.png',renderView1,ImageResolution=[1670,1091])
pvbatch is like pvpython, with two exceptions. pvbatch only accepts
commands from input scripts, and pvbatch will run in parallel if it was
built using MPI. Input is exactly like pvpython.
ssh into one of the clusters. pvbatch can be run on the login nodes, and
magically will acquire compute nodes and run your batch visualization in
parallel. You will find test scripts at /projects/viz/training/paraview.
These scripts are run as follows:
/projects/viz/paraview/bin/pvbatch_chama_mesa
This is version x.x.x of |pvbatch|.Incorrect number of argument supplied. Expecting 4 but have 0Usage: /projects/viz/paraview/bin/pvbatch_chama_mesa <Nodes> <Minutes> <HERT estimate> batchFileFullPath
This tutorial shows how to visualize CTH datasets (called spcth files).
CTH is a multi-material, large deformation, strong shock wave, solid
mechanics code developed at Sandia National Laboratories. A more
complete writeup on CTH is here: http://www.sandia.gov/CTH/. CTH Spyplot
files are Eulerian, or structured mesh datasets. They can be flat mesh
or adaptive mesh refinement (i.e., AMR).
paraview reads spcth files in an very efficient manor. All material
volume arrays go from 0 (representing 0%) to 1 (representing 100%).
These are actually stored in the files as floats (4 bytes) or doubles (8
bytes). paraview reads these into unsigned bytes, which range from 0 to
255. Generally, you want a surface (contour or clip by scalar) at about
10%.
Creating contours with the Extract CTH Parts filter
Our goal is to create a contour where Material Volume Fractions is at 10%.
Start paraview.
Open spcth_a.0.[0-3].
Turn all variables on.
Apply.
Notes:
There are three types of data that have been read in.
Volume data is the structured data from the CTH simuliation
Tracers are points in the mesh that move with a material, and
can include variable information.
Markers are groups of points that move with a material.
Notice the Down Convert Volume Fraction has been checked. This
means that ParaView will store volume fractions as an unsigned
byte.
Y-
Note: Since we will have two materials touching each other, our
default Volume Fraction Value will have some cells visible on top
of each other. If this is not desired, change the value to 0.5.
Coloring by point will be smoother than color by cell. Thus, we will
convert variables to be point for anything we color.
Filters/CTH/Extract CTH Parts.
Turn off all Volume Arrays, except Material volume fraction - 1.
Apply.
Filters → Alphabetical → Cell Data to Point Data.
Apply.
Set Coloring to Pressure.
In the Pipeline Browser, select Volume Data (i.e., the raw cth data again).
Filters → CTH → Extract CTH Parts.
Turn off all Volume Arrays, except Material volume fraction - 2.
Apply.
Change Representation to “Surface With Edges”.
Change Representation back to “Surface”.
With the left mousebutton, grab the 3d view and drag down. This
will rotate the block face down.
With the right mousebutton, grab the 3d view and drag down. This
will move closer to the block face.
Play forward to about the 8th timestep.
Creating a filled isovolume with the Clip by Scalar filter
Our goal is to create a solid 3d isovolume where Material Volume
Fractions is at 10%. We want to do this so we can then take slices
through the object.
Lets start from scratch.
Edit → Reset Session.
Open spcth_a.0.[0-3].
Turn all variables on.
Apply.
We now want to move our data to point based, as opposed to cell based
data.
Filters → Alphabetical → Cell Data to Point Data.
Apply
We now extract one material volume. ParaView has actually read in
Material volume fraction data as an unsigned byte, running from 0 to
255. 10% full is about 25, 50% is 128. Lets create an isovolume at 10%.
Filters → Common → Clip.
Set Clip Type to Scalar.
Set Scalars to Material volume fraction - 1.
Set Value to 25.
Apply.
Turn off visibility of the Cell Data to Point Data filter.
Filters → Common → Slice.
Y Normal.
Apply.
Unselect the Show Plane check box.
Set Coloring to Pressure.
We now want to change the colormap.
View → Color Map Editor. (There is a shortcut icon below the Edit menu.)
Click the Preset icon (little folder with a heart).
Rainbow Desaturated.
Apply.
Close.
Click Rescale to Custom Data Range (small icon below Sources).
Set range from 0 to 2e10.
Select the Volume Data in the pipeline browser.
Filters → CTH → Extract CTH Parts.
Select only Material volume fraction - 2.
Apply.
Filters → Alphabetical → Cell Data to Point Data. (This will smooth out the colors on each cell.)
Apply.
Set Coloring to Temperature (eV)
This image has three slices, opacity turned to 0.5 and the Extract CTH
Parts filter is being painted by temperature.
Analyzing fragments with the Material Interface filter
Our next goal is to analyze the fragments created by this simulation. To
do this, we use the Material Interface Filter.
Lets start again from scratch.
Edit → Reset Session.
Open spcth_a.0.[0-3].
Turn all variables on.
Apply.
This filter is tricky. Do exactly as follows.
Filters → CTH → Material Interface Filter.
In Select Material Fraction Arrays select Material volume fraction - 1 (which is the ball).
In Select Mass Arrays select Mass (g) - 1 (which is the mass array for Material volume fraction - 1).
In Compute volume weighted average over select Pressure and Temperature.
Leave Compute mass weighted average over empty.
Apply
Go to the 10th timestep.
Paint by Pressure.
+Y
Turn off visibility for the geometry in the Pipeline Browser.
This is done by clicking the eyeball.
Anywhere there is a dot is the center of a fragment. We have statistics
for each of these fragments.
Turn on visibility for the geometry in the Pipeline Browser.
Now, lets look at the statistics in the spreadsheet view.
split vertical. (This icon is found in the upper right corner of
the 3d window)
Spreadsheet View
In the Pipeline Browser, click the eyeball for statistics
Each row represents a fragment.
In the Spreadsheet View, click on the Mass column. You have now
sorted the spreadsheet.
The biggest fragment is the top row.
Click on the top row. It is now selected in the 3d view above.
Click in the 3d view, then turn off visibility for the geometry
in the Pipeline Browser. The geometry of the fragment is hiding the
selected statistic point.
Note that you can also change the opacity of the geometry, so you can
see this selected point.
You can also create a 2d plot along a line through your dataset. Here is
how to do it.
Lets start again from scratch.
Edit → Reset Session.
Open spcth_a.0.[0-3].
Turn all variables on.
Apply.
Again, we need a solid surface in which to work.
Set Representation to Surface with Edges.
Set Coloring to Pressure.
-Y.
You can now see where the aluminum ball is hitting the steel block.
Filters → Data Analysis → Plot Over Line.
Apply.
We want to overlay the line horizontally across the area of interest,
just inside of the block. To do this, we will set it on the surface and
then move it.
Click X Axis. The line is now horizontal, through your data. The base
of the arrow is on the right, the head is to the left.
Place the cursor at the right edge of the block, 3/4 of the way to
the top. Hit the 1 key. You have now moved the base.
Place the cursor at the left edge of the block, 3/4 of the way to the
top. Hit the 2 key. You have now moved the head.
Make sure the Plot Over Line filter is still selected.
Apply.
In the Properties tab, un-select all variables that you don’t want to plot.
More details on how to run Plot filters can be found in Section 5 of Tutorials.
This tutorial shows common visualization techniques for cfd datasets. We
will be using the dataset disk_out_ref.ex2, found in Paraview under
File/ Open/ Examples. It has a vector field in it called V. Note that we
will reset session (i.e., start from scratch) every section.
View → Color Map Editor → Presets (the little envelope with a heart) → Turbo.
With the mouse, rotate the slices around so you can see both surfaces.
Edit → Reset Session. There is also a shortcut icon just above
where you have been changing colors. It looks like a green
counterclockwise snake eating it’s tail.
Lines don’t color as nicely as surfaces. Lets add a tube filter around
each streamline.
Select Filters → Search
Type Tube.
Apply.
Now, we want to know which directions the particles are moving. We will
use a glyph filter. Note we place the glyph filter on the streamline,
not the tube.
Select StreamTracer1 in the Pipeline Browser.
Select Filters → Common → Glyph.
Set Glyph Type to Cone.
Set Orientation Array to v.
Set Scale Array to v.
!Very Important!: In the Scale Factor select the recycle button to the right.
Apply.
Set Coloring to temp.
View → Color Map Editor → Presets (the little envelope with a heart) → Black Body Radiation.
We want to create stream tracers from any arbitrary source. This can be
a line, spline, circle, elipse or any other curving line. An extreme
example would be a cylinder cut by a plane.
Open disk_out_ref.ex2.
Apply.
+X
Set vtkBlockColors to Solid Color.
Set Opacity to 0.3.
Sources/Alphabetical/Elipse.
Set Center to 0,0,7.
Set Major Radius Vector to 3,0,0.
Set Ratio to 0.3.
Apply.
Select Filters → Search
Type Tube.
Apply.
Select disk_out_ref.ex2 in the Pipeline Browser.
Select Filters → Alphabetical → Stream Tracer with Custom Source.
Set Seed Source to Elipse.
Apply.
Set Coloring to Solid Color.
The image below is a merging of Stream Tracers with lines and tubes, and
Stream Tracer with Custom Source. I have also played with colors to make
it look nicer. If interested, replicating is left to the user.
To show a velocity profile we need to sample the dataset with a line,
and then create glyphs off of this line. This can be done using a trick
in ParaView, i.e., the Plot over Line filter. Note that a Resample to
Line filter will be added in ParaView 5.11 or so.
Edit → Reset Session.
Open disk_out_ref.ex2.
Apply.
Lets sample over a line.
Select Filters → Data Analysis → Plot over Line.
Y Axis.
Change the Z component of Point1 and Point2 to 1.
Change the Resolution to 40.
Apply.
Close the LineChartView.
In the Pipeline Browser, turn visibility off for disk_out_ref.ex2.
We now have a line sampled through the fluid. Lets calculate the
negative Z component of V (so it goes the opposite direction on the line
from V). That way we can have two profiles, one with V, and one with Vz.
Set Filters → Common → Calculator.
Change Result to Vz.
Set Expression to 0*iHat+0*jHat+-v_Z*kHat.
Apply.
Now we want to create two Glyphs - one from the Calculator filter,
and one directly from the Plot over Line filter.
Calculator1 should still be highlighted in the Pipeline Browser.
Select Filters → Common → Glyph.
Set Glyph Type to Arrow.
Set Orientation Array to Vz.
Set Scale Array to Vz.
!Very Important!: In Scale Factor select the recycle button to the right.
.5X.
.5X.
Apply.
Click on the Color Editor icon.
Change the color to Orange.
Apply.
In the Pipeline Browser select the Plot over Line filter.
Select Filters → Common → Glyph.
Set Glyph Type to Arrow.
Set Orientation Array to v.
Set Scale Array to v.
!Very Important!: In Scale Factor select the recycle button to the right.
Apply.
Let’s put these glyphs back into context by showing the original dataset.
Select disk_out_ref.ex2 in the Pipeline Browser.
Click on the eyeball next to disk_out_ref.ex2.
Set Opacity to 0.3.
Just to create a nice image, I’m going to split the views horizontally,
and show this visualization also from the side.
You can write the data sampled down the line to a .csv file, where you
can post process it with tools such as Excel. Here is how to do it.
Select PlotOverLine in the Pipeline Browser.
Split screen vertical.
Spreadsheet view.
Now, click on the Export Scene icon, and write the
Spreadsheet down to a .csv file.
The Gradient filter (Advanced Properties tab) provides Gradient,
Divergence, Vorticity and and Q Criterion. Here is am example, using
disk_out_ref.ex2.
There are numerous ways to probe the cells and points of a fluid. One is
with the Hover Points On and Hover Cells On icons just above the
Renderview. Another is with Interactive Select Cells or Points On. Then,
in the Find Data, turn on Cell or Point Labels. Yet another is with the
Probe filter. Here is how to use the probe filter.
Edit → Reset Session.
Open disk_out_ref.ex2.
Apply.
+X.
Select Filters → Common → Clip.
Uncheck Show Plane.
Uncheck Invert.
Apply.
The Probe filter works much better with Auto Apply turned on.
This is the icon that looks like a tree growing out of a cube.
Auto Apply on
Select Filters → Data Analysis → Probe.
If needed, select the RenderView window, giving it focus.
Now, move over disk_out_ref.ex2, updating the probed location with the p
key. The probed data will show in the Spreadsheet view.
If you have a vector field in your data, you can animate a static
dataset. Our goal is to create a set of streamlines from a vector field, place
points on this set of streamlines, and animate the point down the
streamlines. We will also add glyphs to the streamline points.
Edit → Reset Session.
Open disk_out_ref.ex2.
Apply.
Click the -X icon.
Stream tracer filter. (We are already streamtracing on V).
Set Seed Type to Point Cloud.
Optional - change the Opacity to 0.4.
Apply.
Select Filters → Common → Contour.
Contour on IntegrationTime.
Apply.
Select Filters → Common → Glyph.
Vectors V.
No Scale Array.
Scale 1.
Set Glyph Mode to All Points.
Apply.
Select View → Animation View.
Set Mode to Sequence.
Set No. Frames to 100.
Change the pulldown box next to the blue + to be Contour.
Click the blue +. Note it works better if you use 0 for the start.
Now, click the play button.
In the pipeline browser, I also turned off visibility for the Contour filter.
We are going to paint the fluid by volume rendered temperature and we will try to make it look like fire.
To give context, we are also going to extract the exterior surface, and clip the
disk_out_ref in half. We will paint this exterior surface black.
Note: Volume rendering is very resource intensive. It is possible to display a dataset
using surface that chokes using Volume Rendering. The solution is to grab more nodes of
your cluster, thus picking up more memory.
Edit → Reset Session.
Open disk_out_ref.ex2
Apply.
Select Filters → Alphabetical → Extract Surface.
Apply.
Select Filters → Common → Clip.
Deselect Invert.
Apply.
Set Solid Color to black.
Set Representation to Wireframe.
Open disk_out_ref.ex2 again.
Apply.
Set Coloring to temp.
Set Representation to Volume.
Since the goal is to make it look like fire, we will finetune the Color Map settings.
Select View → Color Map Editor
Change presets (looks like a folder with a heart) to be Black Body Radiation.
The Color Transfer function (the lower 1D colored line) should already have 4 points.
Add a point in the orange area
Add another at the top of the black.
Did you know?
You can create a point on the color scale by clicking in the window.
You can select a point on the color scale by clicking on it.
You can move between points using the Tab and Shift keys.
You can delete points using the delete key.
The temperature should be set by the physical laws of black ody curve. Thus,
manually specify the color transfer function values of the 6 points as follows
by clicking the advanced button.
The Opacity Transfer function (the upper 2D colored line) should already have 2 points.
Add 4 extra points as seen bellow.
The Opacity requires a bit of artistic license. What we are trying to
do is show the different temperatures inside of the flame. Also, we
may want to show differing amounts of soot - which will be point
number1. Thus, manually specify the opacity transfer function values
of the 6 points as follows.
The end result of the volume rendered fire should look like this:
Particle simulations consist of point data, rather than cell or element
data. An example may be electrons in a field, or water molecules in a
fluid. Particle datasets can be combined with other datasets to show
particle motion in a solid or liquid.
This tutorial uses a dataset named mediumVector.vtu. I will try to get
it on the Kitware web site. If you want to make it yourself, it is just
a vtk dataset, using the format listed at the end of this tutorial. I
then read it into ParaView, and used the reflect filter in the X, then
Y, then Z direction. I believe I then did the same reflections again.
Finally, this file was written out to disk as a .vtu file.
You may want to replace these particles with spheres or arrows, using
the glyph filter. The glyph filter will depopulate your dataset to a
reasonable number of items, and this reasonable number is set by the
Maximum number of points input box. Random mode often creates
better looking output, but is not useful if you animate through
numerous time steps. The following picture has arrows for particles,
using vectors for direction and length, and colored by temperature.
Another filter that is useful is the Filters → Alphabetical → Threshold.
Using the Threshold filter, a user can select only those particles that are
of interest. For instance, the following picture only displays
particles that have a temperature of 430 to 511 degrees. Using the
Filters → Common → Clip, the upper half of the picture has arrow glyphs, and
the lower half has the particles themselves - all colored by temperature.
Finally, you can make a scatter plot through the Filters → Common → Calculator.
For instance, if we want to preserve the X and Y coordinates of our points, but
use number of pizzas for the Z component, we would do the following:
Select Filters → Common → Calculator.
Check the Coordinate Results check box.
Set Expression to coordsX*iHat+coordsY*jHat+pizza*kHat. This
creates a vector, as follows: (X,Y,pizzas). (Think of the iHat as
“This is an X”, the * as tying the coordinates and variables
together, and the + sign as the comma between X,Y, and Z.)
This data is written to a .vtk file. Note that I have deleted a lot of
the data, which will need to be recreated. Also note that I added some
random variable data - for instance, some locations have 1 or 2 pizzas.
This actually creates a strange dataset - with many points per cell, but
it worked for display purposes.
ParaViewWeb, is a Web framework to build applications with interactive
scientific visualization inside the Web browser. Those applications can
leverage a VTK and/or ParaView backend for large data processing and
rendering.
There are example prototypes that have been built using the ParaViewWeb
framework. Here is a webpage that has 4 of them -
https://pvw.kitware.com/.
Visualizer is a web based prototype of ParaView using the ParaView Web
framework. Click on the Visualizer icon. This brings up a web client,
connecting to a backend server located at Kitware headquarters, in
Clifton Park, New York. Visualizer can connect to any ParaView server,
but in this case they use Kitware headquarters.
In the upper left corner are menu options. Running from the left side,
these icons are:
Pipeline view.
Open File.
Note that this is wherever the server is located. In this
example, it is in New York state.
Filters.
This is a subset of the ParaView Filters. Note that almost
any ParaView filter can be exposed, customizing this list to the
needs of the user.
Save Screenshot.
This will save locally or remotely, depending on the needs of the user.
Information.
This will give information for whatever filter is
selected in the pipeline browser.
J. Ahrens, K. Brislawn, K. Martin, B. Geveci, C.C. Law, and M. Papka. Large-scale data visualization using parallel data streaming. IEEE Computer Graphics and Applications, 21(4):34–41, 2001. doi:10.1109/38.933522.
ALS+00
James Ahrens, Charles Law, Will Schroeder, Ken Martin, Kitware Inc, and Michael Papka. A parallel approach for efficiently visualizing extremely large, time-varying datasets. Technical Report LAUR-00-1620, Los Alamos National Laboratory, 2000.
ADM+07
James P Ahrens, Nehal Desai, Patrick S McCormick, Ken Martin, and Jonathan Woodring. A modular extensible visualization system architecture for culled prioritized data streaming. In Visualization and Data Analysis 2007, volume 6495, 176–187. SPIE, 2007.
BGM+07
John Biddiscombe, Berk Geveci, Ken Martin, Kenneth Moreland, and David Thompson. Time dependent processing in a parallel pipeline architecture. IEEE Transactions on Visualization and Computer Graphics, 13(6):1376–1383, 2007. doi:10.1109/TVCG.2007.70600.
BS08
Jasmin Blanchette and Mark Summerfield. C++ GUI Programming with Qt 4 (2nd Edition) (Prentice Hall Open Source Software Development Series). Prentice Hall, hardcover edition, 2 2008. ISBN 978-0132354165.
CGM+06
Andy Cedilnik, Berk Geveci, Kenneth Moreland, James Ahrens, and Jean Favre. Remote Large Data Visualization in the ParaView Framework. In Alan Heirich, Bruno Raffin, and Luis Paulo dos Santos, editors, Eurographics Symposium on Parallel Graphics and Visualization. The Eurographics Association, 2006. doi:10.2312/EGPGV/EGPGV06/163-170.
Kitware and Inc. VTK User's Guide. Kitware, Inc., paperback edition, 3 2010. ISBN 978-1930934238.
MT03
K. Moreland and D. Thompson. From cluster to wall with vtk. In IEEE Symposium on Parallel and Large-Data Visualization and Graphics, 2003. PVG 2003., volume, 25–31. 2003. doi:10.1109/PVGS.2003.1249039.
MWP01
K. Moreland, B. Wylie, and C. Pavlakos. Sort-last parallel rendering for viewing extremely large data sets on tile displays. In Proceedings IEEE 2001 Symposium on Parallel and Large-Data Visualization and Graphics (Cat. No.01EX520), volume, 85–154. 2001. doi:10.1109/PVGS.2001.964408.
Mor13
Kenneth Moreland. A survey of visualization pipelines. IEEE Transactions on Visualization and Computer Graphics, 19(3):367–378, 2013. doi:10.1109/TVCG.2012.133.
MAF07
Kenneth Moreland, Lisa Avila, and Lee Ann Fisk. Parallel unstructured volume rendering in ParaView. In Robert F. Erbacher, Jonathan C. Roberts, Matti T. Gröhn, and Katy Börner, editors, Visualization and Data Analysis 2007, volume 6495, 144 – 155. International Society for Optics and Photonics, SPIE, 2007. URL: https://doi.org/10.1117/12.704533, doi:10.1117/12.704533.
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Will Schroeder, Kenneth W. Martin, and William E. Lorensen. The visualization toolkit: An object-oriented approach to 3D graphics. Kitware, 2006. ISBN 1-930934-19-X.
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William J. Schroeder, Kenneth M. Martin, and William E. Lorensen. The design and implementation of an object-oriented toolkit for 3d graphics and visualization. In Proceedings of the 7th Conference on Visualization '96, VIS '96, 93–ff. Los Alamitos, CA, USA, 1996. IEEE Computer Society Press. URL: http://dl.acm.org/citation.cfm?id=244979.245018.
button from the toolbar.
button in the 
button
on the 
and 
are often
used in this widget to give you an indication of whether the array is
cell-centered or point-centered, respectively.
are used
to indicate cell, point, and field data arrays. Since data arrays can have multiple
components, the range for each component of the data array is shown.
button in the tab bar. You can close a tab, which will destroy all views laid out
in that tab, by clicking on the 
button.
To pop out an entire tab as a
separate window, use the 
button on the
tab bar.
button or search for it by name using the search
box.
button enables you to select columns to
show. Click on the button to get a popup menu in which you check/uncheck the
columns to show/hide.
If showing 
button, when
checked, enables you to see the point ids that form each of the cells.
button to make the view show only selected elements. Now, as you make selections
in other views, this 
button to create
this filter.
button on the 
To specify the region of interest, use the 
on the 
button on the 
button next to the 
button on the 
The type of selection you are
creating will depend on the button you clicked. Once in
non-interactive selection mode, the cursor will switch to cross-hair
and you can click and drag to create a selection region. Once you
release the mouse,
ParaView will attempt to create a selection for any elements in the selection
region and will go back to default interaction mode.
. In interactive
selection mode, you act on visible elements (cells or
points). ParaView highlights elements of the dataset as you move
the cursor over them. An element can be selected by clicking on
it. Clicking repeatedly on different elements adds them to the
selection. End the interactive selection mode by clicking on
the interactive selection button pushed in or by pressing the
Esc key. This mode is also ended when you enter a
non-interactive selection mode. Use 
button can be used to clear the selection.
, remove :
, toggle : 
. These modifiers do not work,
however, if the selected data is different from the current selection. If so, the
current selection will be cleared (as is the norm) and then the new selection will be created.
. Once in selection mode, you
can click and drag to define the selection region. The selection is created once
you release the mouse press.
button on the 
button.
button in the view toolbar to show only selected elements.
from the 
button in the 
copies the current set of property values to the
clipboard while clicking the 
will paste those
property values into another compatible panel section. Note that the paste icon
is enabled only for panel sections where the copied properties can be pasted.
enable customizing the default values
used for those properties. Refer to Section 12.2
to learn more about customizing default property values.
button. When unchecked,
you will need to manually update the panel using the 
and 
described later.
: Rescales the color and opacity transfer
functions using the data range from the data source selected in the Pipeline
browser, i.e., the active source. This rescales the entire transfer function.
Thus, all control points including the intermediate ones are proportionally
adjusted to fit the new range.
: Rescales the color and opacity transfer
functions using a range provided by the user. A dialog will be popped up for
the user to enter the custom range.
: Rescales the color and
opacity transfer functions to the range of values for data over all
timesteps. This operation may be costly as data for all timesteps
needs to be read.
: Rescales the color
and opacity transfer functions using the range of values for the
elements (cells or points) visible in the view. This operations
assigns the entire range of colors to visible elements which may
reveal patterns not visible otherwise.
: Inverts the color transfer function
by moving the control points, e.g,. a red-to-green transfer function will be
inverted to a green-to-red one. This only affects the color transfer function and
leaves the opacity transfer function untouched.
button near the top of
the panel. This button affects the visibility of the legend in the active view.
button on the 
and 
buttons can be used to fill the
annotations widget with unique discrete values from a data array, if
possible. Based on the number of distinct values present in the data
array, this may not yield any result (Instead, a warning message will
be shown). The data array values come either from the selected source object
if you use the 
button next to the parameter name.
icon in the toolbar to bring up the
icon changes from 
. Second, you can explicitly override the color to use
for a block or a subtree. To do this, simply double click on the color column
next to the block of interest. This will pop up the color chooser dialog.
Explicitly overridden color for a block is indicated by a solid filled circle
icon 
filled with the selected color.
When an explicit color is set on a non-leaf node, all its children (and their
children) inherit that color unless explicitly overridden. For such nodes that
have a color inherited from their parent, we use the dotted-circle icon filled
with a pattern icon 
.
, or explicitly set
, or inhertied from parent node
.
to accept the default
parameters.
button performs a reset camera such that it maintains
the same view direction but repositions the camera such that the entire
object can be seen. The second button 
performs a
zoom to data. It behaves very much like reset camera except that
instead of positioning the camera to see all data, the camera is placed
to look specifically at the data currently selected in the pipeline
browser. The third button 
performs a
reset camera closest such that it maximizes the occupation,
in the screen, of the whole scene bounding box. The fourth button
performs a zoom closest to data. It behaves
very much like reset camera closest except that instead of positioning
the camera to see all data, the camera is placed to look specifically
at the data currently selected in the pipeline browser. You currently
only have one object in the pipeline browser, so right now reset camera
and zoom to data, and reset camera closest and zoom closest to data will
perform the same operation.
allows
you to select a rectangular region of the screen to zoom to (a rubber-band zoom).
The following six buttons, starting with 
, reposition the camera to view
the scene straight down one of the global coordinate’s axes in either
the positive or negative direction. The rightmost two buttons 
rotate the view either clockwise or counterclockwise. Try
playing with these controls now.
allows you to pick the center of rotation. Try clicking that button then
clicking somewhere on the cylinder. If you then drag the left button in
the 3D view, you will notice that the cylinder now rotates around this
new point. The next button to the left 
replaces the center
of rotation to the center of the object. The next button to the left 
shows or hides axes drawn at the center of rotation. (You probably will not notice
the effects when the center of rotation is at the center of the cylinder
because the axes will be hidden by the cylinder. Use the pick center of
rotation 
toggles showing the
orientation axes, the always-viewable axes in the lower left corner
of the 3D view.
will revert the options back to the last time they
were applied. Hit the Apply button now. The resolution is changed so that
it is virtually indistinguishable from a true cylinder.
button under Coloring to select a new color for the cylinder. (This
button is also replicated in the toolbar.) You may notice that you do
not need to hit Apply for display properties.
in the toolbar.
and redo 
buttons in the toolbar.
Visualizing your data is often an exploratory process, and it is often
helpful to revert back to a previous state. You can even undo back to
the point before your data were created and redo again.
and redo camera 
buttons at the view’s
toolbar. These allow you to go back and forth between camera angles that
you have made so that you do not have to worry about errant mouse
movements ruining that perfect view. Move the camera around and then use
these buttons to revert and restore the camera angle.
in the properties panel.
Calculator
Contour
Warp (vector)
Group Datasets
Extract Level
in the properties panel.
next to them. But
also notice the indentation of the entries in the list and the
connecting lines toward the left. These features reveal the
connectivity of the pipeline. It shows the same information as the
traditional graph layout on the right, but in a much more compact space.
The trouble with the traditional layout of pipeline objects is that it
takes a lot of space, and even moderately sized pipelines require a
significant portion of the GUI to see fully. The pipeline browser,
however, is complete and compact.
and 
buttons, respectively. The 
button deletes a view, whose
space is consumed by an adjacent view. The 
temporarily fills view space
with the selected view until 
is pressed.
on the
toolbar. This option deletes all of your current work and resets
ParaView back to its initial state. It is roughly the equivalent of
restarting ParaView.
next to Clip1 in the pipeline browser.
button to get a straight-on view of the cross section and
zoom in a bit.
in the properties
panel under the seed type.
Compute Quartiles
Extract Selection
Histogram
Plot Global Variables Over Time
Plot Over Line
Probe
Save Screenshot. Additionally, if you choose File
→ Export Scene… you can export a file with vector
graphics that will scale properly for paper-quality images. We will
discuss these image capture features later in Section 2.13.
You can also resize and swap plots in the GUI like you can other views.
button to orient the camera to the mesh.
.
).
button toggles locking the aspect ratio when selecting
an image resolution. The 
.
query mode
and a hover cell 
query mode that allow you to quickly inspect the field
values at a visible point by hovering the mouse over it. There is also a
clear selection button that will remove the current selection.
the animation.
toolbar button. You can find documentation for all the available
pipeline objects under the Sources, Filters, Readers, and Writers
entries in the help Contents. Each entry gives a list of objects of that
type. Clicking on any one of the objects gives a list of the properties
you can set from within Python.
buttons. When ParaView starts,
it automatically connects to the builtin server. It also connects to
builtin whenever it disconnects 
icon is on the left side of the row
of icons at the top left of the 3d window.
