[vtkusers] Volume Cropping not working...

[C C]

Hi all,
  I'm looking to crop my 3d volume so as to not display the fringes of
my dataset.  I've been struggling to get this to work but thus far
nothing is responding (the image is displaying as a whole).  Can
vtkFixedPointVolumeRayCastMappers not be cropped?  or is there
something else wrong w/ the code below:

////////BEGIN-CODE////////////
vtkFixedPointVolumeRayCastMapper *volumeMap =
vtkFixedPointVolumeRayCastMapper::New();
double cropBounds[6];
    cropBounds[0] = 10;
    cropBounds[1] = 50;
    cropBounds[2] = 10;
    cropBounds[3] = 50;
    cropBounds[4] = 20;
    cropBounds[5] = 30;
volumeMap->CroppingOn();
volumeMap->SetCroppingRegionPlanes( cropBounds );
volumeMap->SetCroppingRegionFlagsToSubVolume();
volumeMap->SetInput( imageData ); //imageData is my volume, loaded earlier
////////END-CODE////////////

The above was adopted from the tcl example in the vtk user manual on
page 124.  Again, the cropping is not modifying the dataset in any
way...  I will be greatful for any insights!  thanx,

-cc