This morning I added a new geometry filter to VTK. It does clipping with an important extra feature: it treats the surface geometry as a topologically closed surface, so that if you give it a closed surface as an input, it will produce a closed surface as an output. Perhaps a better way of saying this is that it treats the data like a solid object, instead of treating it like just a collection of polygons. There are several applications for such a filter in VTK:

• Generating and manipulating data for use in stereolithography a.k.a. 3D printing.
• Visualization of arbitrary closed clipping regions (which is what I originally developed it for).
• Generating closed geometries for use in GPU volume rendering
• FEM model creation (though a triangle refinement step would be necessary)

A more complete description is provided on the VTK wiki page: http://www.vtk.org/Wiki/VTK/Closed_Surface_Clipping.