Unable to clip properly for volume rendered visualization


I have a python script that is supposed to do a box clip on a volume rendered image, but the clipping seems wrong and I’m not sure how to fix it.

I copied my code into ParaView and ran it in the Python shell and it gets me this:

which is not what I wanted. However, viewing the properties panel (and hence showing the box) fixed the problem:

but since I’m running the script using pvpython i.e. without the GUI, there is no way I could write a line of code that “opens the properties panel” (tracing in ParaView showed nothing).

It also seems that the faulty clip is only clipping a quarter of the box (top-right). Is this a bug, or is there any way I can fix this?

I’m running on ParaView 5.6.0 64-bit. Here’s part of the code that does the clipping:

from paraview.simple import *
import numpy as np

disable automatic camera reset on ‘Show’


Define global variables

Ro = 22.25/1000.0
Ri = 17.46/1000.0
L = 1000/1000.0
ecc = 46./100.0
delta = -(Ro-Ri)*ecc # delta is a negative value

create a new ‘OpenFOAMReader’

case3foam = OpenFOAMReader(FileName=’/home/etrati/Documents/OpenFOAM/newtonian/case2/case2.foam’)

case3foam.CaseType = ‘Reconstructed Case’
case3foam.LabelSize = ‘32-bit’
case3foam.ScalarSize = ‘64-bit (DP)’
case3foam.Createcelltopointfiltereddata = 1
case3foam.Adddimensionalunitstoarraynames = 0
case3foam.MeshRegions = [‘internalMesh’]
case3foam.CellArrays = [‘alpha.heavy’]
case3foam.PointArrays = [‘alpha.heavy’]
case3foam.LagrangianArrays = []
case3foam.Cachemesh = 1
case3foam.Decomposepolyhedra = 1
case3foam.ListtimestepsaccordingtocontrolDict = 0
case3foam.Lagrangianpositionswithoutextradata = 1
case3foam.Readzones = 0
case3foam.Copydatatocellzones = 0

get active source.

case3foam is the file that we want to load

case3foam = GetActiveSource()

set active source


get active view

renderView1 = GetActiveViewOrCreate(‘RenderView’)

Properties modified on renderView1

renderView1.CameraParallelProjection = 1

show data in view

case3foamDisplay = Show(case3foam, renderView1)


get active source.

openFOAMReader1 = GetActiveSource()

get display properties

openFOAMReader1Display = GetDisplayProperties(openFOAMReader1, view=renderView1)

set scalar coloring

ColorBy(openFOAMReader1Display, (‘CELLS’, ‘alpha.heavy’))

rescale color and/or opacity maps used to include current data range

openFOAMReader1Display.RescaleTransferFunctionToDataRange(True, False)

show color bar/color legend

openFOAMReader1Display.SetScalarBarVisibility(renderView1, True)

get color transfer function/color map for ‘alphaheavy’

alphaheavyLUT = GetColorTransferFunction(‘alphaheavy’)

get opacity transfer function/opacity map for ‘alphaheavy’

alphaheavyPWF = GetOpacityTransferFunction(‘alphaheavy’)

change representation type


create a new ‘Clip’

clip1 = Clip(Input=openFOAMReader1)

get animation scene

animationScene1 = GetAnimationScene()

update animation scene based on data timesteps


toggle 3D widget visibility (only when running from the GUI)


Properties modified on clip1

clip1.ClipType = ‘Box’
clip1.Invert = 0

Define variables for clipping

xpos = 0
xscale = 1
ypos = delta - Ri
yscale = 2*Ri/Ro

Properties modified on clip1.ClipType

clip1.ClipType.Position = [xpos, ypos, 0.0]
clip1.ClipType.Scale = [xscale, yscale, 1.0]

show data in view

clip1Display = Show(clip1, renderView1)

Properties modified on openFOAMReader1

openFOAMReader1.MeshRegions = [‘internalMesh’]
openFOAMReader1.CellArrays = [‘alpha.heavy’]

update the view to ensure updated data information


change representation type


hide data in view

Hide(openFOAMReader1, renderView1)

Thanks in advance!

Looks like your python code is incorrect. What was needed to do manually in the properties panel ?

For the clipping, it is to specify the clip type (box) and no invert as well as specifying the clip dimension. Apart from that, it’s just setting the camera parallel projection. Nothing was changed when I view the properties panel after running the code. Does that answer your question?

The python code is mostly copied from the ParaView trace function, except adding a few user-defined variables and moving blocks of code around for troubleshooting. Any help would be appreciated!