[vtkusers] Volume Rendering using RayCastMapper

[Prasenjit Roy]

dear vtkusers,
  I am experiencing problem in volume rendeing using vtkvolumeRayCastMapper and using vtkVolumeRayCastCompositeFunction when I use a Color and opacity funtion to make most of my volume voxels transparent but viewing only some specific scalar range values. I am getting a "VTK RENDERING ERROR" and the execution time is terribly slow for a moderate size voxel (50,50,50).
   
  I know that, I might be doing something wrong as it is very common to see a floating volume using VTK and also in VolView. 
   
  Please let me know your views. Any help is highly appreciated. Please find below the sample code.
   
  Many Thanks.
  Prasenjit Roy.
   
  // Image Data 8bit [data8bit is an input]
     vtkImageData *image3Ddata = vtkImageData::NEW;
 image3Ddata->SetDimensions(dim[0],dim[1],dim[2]);
 image3Ddata->SetOrigin(org[0],org[1],org[2]);
 image3Ddata->SetSpacing(sp[0],sp[1],sp[2]);
 image3Ddata->SetScalarTypeToUnsignedChar();
 image3Ddata->SetNumberOfScalarComponents(1);
 image3Ddata->AllocateScalars();
 unsigned char *ptr8 = (unsigned char *) image3Ddata->GetScalarPointer();
 ubound = (dim[0]*dim[1]*dim[2]);
 for (k=0; k<ubound; k++)
 {
  *ptr8++ = (unsigned char) data8bit[k];
 }
  // Set Opacity
    vtkPiecewiseFunction *opacityFn = vtkPiecewiseFunction::New();
 opacityFn->RemoveAllPoints(); 
 opacityFn->AddPoint(200,0.2);   // Scalar value ranges from [0 to 255]-8bit image data
 opacityFn->AddPoint(225,1);
 opacityFn->AddPoint(255,0.2);
  // Set Color
   vtkColorTransferFunction *colorFn = vtkColorTransferFunction::New(); 
 for(i=0;i<nColors;i++)
 {
  cgp3d_colorFn->AddRGBPoint(cValue[i],R[i],G[i],B[i]);
 }
  //Vol Property
   vtkVolumeProperty *volProp = vtkVolumeProperty::New(); 
 volProp->ShadeOn();
 volProp->SetInterpolationTypeToLinear();
 volProp->SetScalarOpacity(opacityFn);
 volProp->SetColor(colorFn);
     vtkVolumeRayCastCompositeFunction *raycastFn = vtkVolumeRayCastCompositeFunction::New();
 raycastFn->SetCompositeMethodToClassifyFirst();
     vtkVolumeRayCastMapper *volMapper = vtkVolumeRayCastMapper::New();
 volMapper->AutoAdjustSampleDistancesOn();
 volMapper->SetMinimumImageSampleDistance(1);
 volMapper->IntermixIntersectingGeometryOn();
 volMapper->SetVolumeRayCastFunction(cgp3d_raycastFn);
 volMapper->SetInput(image3Ddata);  // image3Ddata is vtkImageData
     vtlVolume *volActor = vtkVolume::New(); 
 volActor->SetMapper(volMapper);
 volActor->SetProperty(volProp);
  
   ren1->AddVolume(volActor);
 




Prasenjit Roy


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