[Paraview] Volume Rendering with NumberOfScalarComponents > 1

[Aashish Chaudhary]

Axel

We were just discussing this few days ago. Do you have to use paraview gui? Or paraview python will work? There might be a way in pv python route. 

Thanks 

Sent from my iPhone

> On Dec 16, 2015, at 5:01 AM, Axel Kittenberger <axkibe at gmail.com> wrote:
> 
> Hello,
> 
> the Python VTK script below gives results, like a expect. Now I'm trying to reproduce it in Paraview and I fail.
> 
> I get rather confused as soon I give it a source with more than one scalar component. 
> Paraview creates one color map; I would expect 3 color maps, 1 for every component.
> What ever I do effective opacity is always 1. That is I see a black cube with it's surface the images
> of the data on its surface (so far correct), however no effective volume rendering -- I selected Volume, "Ray Cast Only"
> which should be vtkFixedPointVolumeRayCastMapper as far I understood.
> 
> I tried creating 3 readers with the different scalar components extracted first, but doesn't give
> correct rendering -- neither in VTK nor in paraview, since multiple renderer seem to compete which gets to
> draw a pixel instead of composing them together
> like a red transparent + a green transparent should give a yellow transparent impression.
> 
> How can I achieve the same result with Paraview?
> 
> Kind regards, Axel
> 
> --------------------------
> #!/usr/bin/env python
> 
> import vtk
> 
> # Create the standard renderer, render window and interactor
> ren = vtk.vtkRenderer( )
> renWin = vtk.vtkRenderWindow( )
> renWin.AddRenderer( ren )
> iren = vtk.vtkRenderWindowInteractor( )
> iren.SetRenderWindow( renWin )
> 
> reader = vtk.vtkImageReader2( )
> reader.SetFileName( "./data.raw" );
> reader.SetDataScalarTypeToUnsignedChar( );
> reader.SetNumberOfScalarComponents( 3 );
> reader.SetFileDimensionality( 3 );
> reader.SetDataExtent( 0, 261, 0, 511, 0, 21 );
> reader.SetDataSpacing( 1, 1, 3.5 );
> 
> # Create transfer mapping scalar value to opacity
> opacityTransferFunction = vtk.vtkPiecewiseFunction( )
> opacityTransferFunction.AddPoint(   0, 0.0 )
> opacityTransferFunction.AddPoint(  20, 0.0 )
> opacityTransferFunction.AddPoint(  40, 0.1 )
> opacityTransferFunction.AddPoint( 255, 0.1 )
> 
> # Create transfer mapping scalar value to color
> 
> colorRedTransferFunction = vtk.vtkColorTransferFunction( )
> colorRedTransferFunction.AddRGBPoint(   0.0, 0.2, 0.0, 0.0 )
> colorRedTransferFunction.AddRGBPoint( 255.0, 1.0, 0.0, 0.0 )
> 
> colorGreenTransferFunction = vtk.vtkColorTransferFunction( )
> colorGreenTransferFunction.AddRGBPoint(   0.0, 0.0, 0.2, 0.0 )
> colorGreenTransferFunction.AddRGBPoint( 255.0, 0.0, 1.0, 0.0 )
> 
> colorBlueTransferFunction = vtk.vtkColorTransferFunction( )
> colorBlueTransferFunction.AddRGBPoint(   0.0, 0.0, 0.0, 0.0 )
> colorBlueTransferFunction.AddRGBPoint( 255.0, 0.0, 0.0, 1.0 )
> 
> volumeProperty = vtk.vtkVolumeProperty( )
> volumeProperty.SetColor( 0, colorRedTransferFunction )
> volumeProperty.SetColor( 1, colorGreenTransferFunction )
> volumeProperty.SetColor( 2, colorBlueTransferFunction )
> 
> volumeProperty.SetScalarOpacity( 0, opacityTransferFunction )
> volumeProperty.SetScalarOpacity( 1, opacityTransferFunction )
> volumeProperty.SetScalarOpacity( 2, opacityTransferFunction )
> volumeProperty.SetInterpolationTypeToLinear( )
> 
> volumeMapper = vtk.vtkFixedPointVolumeRayCastMapper( )
> volumeMapper.SetInputConnection( reader.GetOutputPort( ) )
> volumeMapper.SetNumberOfThreads( 1 )
> 
> volume = vtk.vtkVolume( )
> volume.SetMapper( volumeMapper )
> volume.SetProperty( volumeProperty )
> 
> ren.AddVolume( volume )
> ren.SetBackground( 1, 1, 1 )
> renWin.SetSize( 600, 600 )
> 
> def CheckAbort( obj, event ):
>     if obj.GetEventPending( ) != 0:
>         obj.SetAbortRender( 1 )
> 
> renWin.AddObserver( "AbortCheckEvent", CheckAbort )
> 
> iren.Initialize( )
> renWin.Render( )
> iren.Start( )
> --------------------------
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