[vtkusers] get visible surface

[Lodron, Gerald]

Hi

I have a surface (vtkPolyData) and camera coordinates.

 I do not want to visualize the scene, I only want to get the current visible triangle as a second vtkPolyData object. I found vtkSelectVisiblePoints but it has two problems:
- it needs a vtkRenderer which needs a vtkRendererWindow, so I always need to display something on real monitor
- it only returns points, I also want surface cells, especially triangles / polygons

Any hints or do I need to reimplement the stuff? Is there also a raycast opportunity?

Best regards

Gerald