[vtkusers] Bounding box of an actor in a specific renderwindow

[Christoph Kolb]

Hello,
I am trying to find an elegant way to get the position and size of a 
rendered object in the renderwindow.
Is there already an algorithm to compute this?
If not: is it appropriate to use the vtkCamera to project the 3D 
bounding box to the renderwindow?

Thank you!
Christoph