[vtkusers] Voxelizing geometry

[Stefan Bruckner]

Hi!

I am trying to voxelize a geometric object and then perform volume
rendering, however, I can't seem to get it working:

vtkSphereSource *sphere = vtkSphereSource::New();
sphere->SetThetaResolution(30);
sphere->SetPhiResolution(30);

vtkVoxelModeller *modeller = vtkVoxelModeller::New();
modeller->SetSampleDimensions(64,64,64);
modeller->SetInput(sphere->GetOutput());

vtkCastToConcrete *caster = vtkCastToConcrete::New();
caster->SetInput(modeller->GetOutput());

I pass the result of "caster->GetStructuredPointsOutput()" to the volume
mapper.

After rather lengthy processing I get the following error message in the
output window, and the rendering shows nothing.

"ERROR: In C:\martink\vtk42\VTK\Filtering\vtkImageToImageFilter.cxx,
line 94
vtkImageClip (0x054BD9A8): ExecuteInformation: Input is not set."

What am I doing wrong? Can anyone please assist me with some sample code
or point me to an example (I didn't mange to find examples for
voxelization).

Thanks, 
Stefan Bruckner