[vtkusers] Augmenting images with polydata

[Tim Soper]

What is the easiest way to overlay/draw 3D polydata onto a 2D image? I have a polydata line that is rendered in a virtual scene that I want to augment onto a video image of the same scene. The trick is that parts of the line are occluded by other polydata surfaces in the scene. So I draw the line in the rendered scene, and want to copy the visible portion (either the line poly data or window pixels themselves) and overlay it onto the 2D image.

I thought I would find similar posts on this but perhaps I am missing some important terminilogy?  

Thanks for any advice

-Tim-