[vtkusers] Voxel visibility

[dce06003]

Hi all.

I have a 3D object, described by an octree, and modeled in VTK by using an
UnstructuredGrid. 
Given a certain viewpoint (image plane), it is possible to know which voxel
is visible for each image pixel?
I know that this is similar to ray casting, where the ray stops when it hits
a voxel.
But I new at VTK and still confused if there are any functions that can help
me...

Thanks and best regards,
				Teresa Azevedo