[vtkusers] vtkImageStencil from arbitrary voxels

[sumit shah]

Dear vtkusers:

I think I have a simple question and a possible solution.  I would  
like to know if this is the best way to approach this problem and if  
my implementation is on track.  I have a vtkImageData object and a  
volume of interest.  This VOI could be anything arbitrary, it is  
simply an array of voxels that are considered to be the VOI ie there  
is no specific intrinsic order or anything of that sort.  I would  
like to render only what is specified by that VOI from the image  
data.  My approach is as follows in this Java snippet:

       vtkVertex vv = new vtkVertex();
       vv.GetPoints().SetNumberOfPoints(roi.numVoxels());

       int i = 0;
       do {
         int x roi.currentPoint().x();
         int z roi.currentPoint().y();
         int y roi.currentPoint().z();

         vv.GetPoints().SetPoint(i++, x, y, z);
       } while(roi.gotoNextPoint());

       vtkCellArray vca = new vtkCellArray();
       vca.InsertNextCell(vv);

       vtkPolyData vpd = new vtkPolyData();
       vpd.SetVerts(vca);

       vtkPolyDataToImageStencil vpdtis = new  
vtkPolyDataToImageStencil();
       vpdtis.SetInput(vpd);

       vis = new vtkImageStencil();
       vis.SetStencil(vpdtis.GetOutput());
// vitsp is an object of type vtkImageStructuredPoints
       vis.SetInput(vitsp.GetOutput());
       vis.SetBackgroundValue(0);
vis.Update();


However this does not seem to work and it crashes on the last line.   
Is this the right approach or is there a more efficient approach?

Thanks,
Sumit