ParaView and Python

Introduction

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.

Overview

ParaView is 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.

A simple Python toy example within ParaView

• Start ParaView.
• Start the Python Interpreter Tools → Python Shell

Notes

You can copy commands from elsewhere and paste them into the Python Shell.

Python is case sensitive. Be sure to use correct capitalization as shown below.

Python is indent sensitive. Be sure to not indent, as shown below.

Lets create and display a sphere.

(Type the following into the Python Shell)

sphere=Sphere()

Show()

Render()

We have now created a sphere in the pipeline, turned on it's visibility, and re-rendered.

Next, lets add a shrink filter. We hide the sphere, add the shrink filter, and re-render.

Hide()

Render()

shrink=Shrink()

Show()

Render()

ParaView will allow us to use either the GUI controls or Python. For instance:

Select the Sphere in the pipeline browser.

In the Python Shell, type the following:

clip=Clip()

Show()

Render()

Or, we could continue in the Python as follows:

clip=Clip()

Hide(shrink)

Show(clip)

Render()

Hide the Plane widget:

Hide3DWidgets(proxy=clip)

Help! (How do we find out what commands are available?)

To see all commands available in ParaView:

dir()

To see all of the options for the Clip creator:

dir(Clip)

To see all of the options for the instance of the clip we created above:

dir(clip)

A better tool to see the available commands for an item in the pipeline is ListProperties, such as:

clip.ListProperties()

Note that this doesn't work on instantiated controls, such as the camera. Use dir() for controls such as camera.

And, to see the different properties of the ClipType variable, use

clip.ClipType.ListProperties()

To see lots of detail on an instance of a command, create the instance and ask for help on that instance..

help(clip)

Change! (Lets look at, and change, something)

Print the Theta Resolution

print(sphere.ThetaResolution)

Change it to 64

sphere.ThetaResolution=64

Show()

Render()

Control input

Lets change the selected filter in the Pipeline Browser:

SetActiveSource(sphere)

Lets delete the clip

Delete(clip)

Lets add a filter to the sphere, without selecting it first

wireframe=ExtractEdges(Input=sphere)

Show()

Render()

A simple Python example reading a datafile and writing a screenshot

• Within the ParaView GUI, Edit → Reset Session
• Start the Python Interpreter Tools → Python Shell

Read in data, use a filter and save a screenshot

Lets read in can.exo, clip can.exo, paint can.exo and save a screenshot.

We use this templagte.

canex2=OpenDataFile('D:/directoryName/can.ex2')

Here is the current path. Be sure to update for version number

canex2=OpenDataFile('C:/Program Files (x86)/ParaView 5.4.1/data/can.ex2')

clip=Clip()

Hide(canex2)

Show(clip)

ResetCamera()

Render()

SaveScreenshot('D:\\directoryName\\picture.jpg')

Information on file readers is found in chapter 2.2 of The ParaView Guide http://www.paraview.org/paraview-guide/

Control time

We want to move forward one timestep, so min and max are set correctly for a variable

animationScene1 = GetAnimationScene()

animationScene1.GoToNext()

Playing through all time is done with the following command.

animationScene1.Play()

We need to acquire the available timesteps:

tk = GetTimeKeeper()

timesteps = tk.TimestepValues

First timestep is found using either of these methods:

animationScene1.GoToFirst()

animationScene1.AnimationTime = timesteps[0]

Last timestep is found using either of these methods:

animationScene1.GoToLast()

animationScene1.AnimationTime = timesteps[-1]

Moving to a specific timestep (such as timestep 10) is done as follows

animationScene1.AnimationTime = timesteps[9] # index starts with 0

To find out how many timesteps we have, you use the len command. Continued on from above.

numTimesteps = len(timesteps)

Available commands are found using:

dir(animationScene1) (after you have created the animationScene1 variable)

dir(GetAnimationScene())

Control the camera

We want to move the camera.

First, get the camera and reset the camera to a known good position.

camera=GetActiveCamera()

camera.SetFocalPoint(0,0,0)

camera.SetPosition(0,0,-10)

camera.SetViewUp(0,1,0)

How to move the camera closer or further away

camera.Dolly(10)

Render()

camera.Dolly(.1)

Render()

How to rotate the camera around the view direction 45 degrees, centered on the dataset. After the reset above, rotate around the X axis.

camera.Roll(45)

Render()

How to rotate the camera around the vector up, centered on the Y axis. After the reset above, rotate around the Y axis.

camera.Yaw(45)

Render()

How to rotate the camera vertically around the camera point

camera.Pitch(45)

Render()

How to rotate the camera around the vector up, centered on the dataset. After the reset above, rotate around the Y axis.

camera.Azimuth(45)

Render()

How to rotate the camera around the X axis, centered on the dataset. After the reset above, rotate around the Y axis.

camera.Elevation(45)

Render()

How to reset the camera

ResetCamera()

Available commands are found using:

dir(camera) (after you have created the animationScene1 variable)

dir(GetActiveCamera())

Paint by a variable

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.

animationScene1 = GetAnimationScene()

animationScene1.GoToNext()

renderView1 = GetActiveViewOrCreate('RenderView')

canex2Display = Show(clip, renderView1)

Get point var names

canexxxx =GetActiveSource()

print ( canexxx.PointVariables.GetAvailable())

Get Cell var names

print ( canexxx.ElementPointVariables.GetAvailable())

For point vars

vars = canex2.PointVariables.GetAvailable()

print (vars)

ColorBy(canex2Display, ('POINTS', vars[0]))

For cell vars

vars = canex2.ElementVariables.GetAvailable()

print (vars)

ColorBy(canex2Display, ('CELLS', vars[0]))

Render() (Actually not needed)

Information on reading variable information is found in chapter 3.3 of The ParaView Guide http://www.paraview.org/paraview-guide/

Scale Around Dataset Center - A userful example

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.

scale_factor = 2

indata = GetActiveSource()

bounds = indata.GetDataInformation().GetBounds()

center = ((bounds[0] + bounds[1])/2, (bounds[2] + bounds[3])/2,(bounds[4] + bounds[5])/2)

transform_to_center = Transform()

transform_to_center.Transform.Translate = [-center[0], -center[1], -center[2]]

Hide()

scale = Transform()

scale.Transform.Scale = [scale_factor, scale_factor, scale_factor]

Hide()

transform_from_center = Transform()

transform_from_center.Transform.Translate = [center[0], center[1], center[2]]

Show()

Render()

Trace Recorder

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.exo, clip can, paint by EQPS, change the camera to +Y, write out a screenshot and write out a movie

• Tools → Start Trace Select Show Incremental Trace.
• File → Open. Open can.exo. OK.
• Turn all variables on.
• Apply.
• +Y
• Clip. Y Normal. Unselect Show Plane. Apply.
• Color by EQPS.
• Last timestep.
• Rescale to Data Range
• First timestep.
• File → Save Screenshot. Save as .png.
• File → Save Animation. Save as .avi.
• Tools → Stop Trace
• File → Save. 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.

Running Scripts

ParaView allows a user to run a script. This is done as follows:

• Tools → Python Shell
• Run Script

Now, browse to your script, and select OK.

Macros

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.
• Click on your Macro on the toolbar.

Python Help

Python documentation (out of date) http://www.paraview.org/Wiki/ParaView/Python_Scripting

The ParaView Guide (Python scattered throughout the guide) http://www.paraview.org/paraview-guide/

Where do you go next?

• ParaView Batch.

Acknowledgements

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.