[vtkusers] ImplicitFunction from vtkPolyData?

[Theodore D. Sternberg]

I'd like to clip one vtkPolyData against a (non-planar) surface defined by
another vtkPolyData.  Image the first vtkPolyData is the Earth, and the
second vtkPolyData is the shape of an impact crater; I'd like to show the
Earth with a crater in it.

To do this, I think I need a vtkImplicitFunction to pass to a
vtkClipPolyData.  Is there a good way to obtain the necessary
vtkImplicitFunction from that second vtkPolyData?

Ted Sternberg
Lawrence Berkeley National Laboratory