[vtkusers] detect vtkActor visibility

[Mathieu Coursolle]

Hi VTK users,

I am displaying a big mesh (head mesh) and a few smaller meshes (spheres) around it.

I position all my vtkActors (small spheres) in the renderer, and then I position my camera based
on some user UI controls.

Once the camera is positioned, is there a way to know which of those small spheres are actually visible
for the user in the view. Can I know which ones are totally hidden by the bigger mesh?

Thank you,

Mathieu