[vtkusers] Representing a volume as a point cloud

[Alex Lear]

Once I've added several volumes to my renderwindow things get very slow.  I 
would like to view the volumes as point clouds instead.  Is there any 
built-in functions for this type of viewing?  If I use vtkPointSource to 
create a point splatter in each voxel, how can they be combined into a single 
point set?

Thank You,

Alex