[vtkusers] How to know if an actor is visible on a scene

[Javier Preciozzi]

Hi !
I have a simple question but I could not found any related information.
I want to load or unload actors depending wether they are visible or  
not on the scene. This is mainly because I want to implement a 3D  
reconstruction of a geographical area which is very large, so I think  
that one possible solution is to generate several actors, and load/ 
unload while moving through the scene. The problem is that I dont  
find a way to determine if an actor is visible or not on the scene.

What do you think ?

Thanks,
Javier