[vtkusers] clip STL surface

[Martin Genet]

Dear VTK users,

I have two STL surfaces, say S1 & S2. I need to measure the area of the 
part of S1 that's "close" to S2.

I thought of creating a third surface that would be a copy of S1 but 
without the cells that are "too far away" from S2. I'm able to use 
vtkDistancePolyDataFilter to create on S1 a field of distance to S2. But 
I can't seem to find a way to "filter" S1 using this distance field and 
a given threshold. Is there such a capability in vtk?

More generally, is there a better way to do what I need to do?

Thanks!

Martin