I've found a partial solution to my previous question about selfintersecting polygons.

- Curvesect with itself - extract - affect left input - extract point
this adds the points of intersection to the existing points (leaving just points, no more primitives)

- Add - polygons - by group
This recreates the polygon

- Fuse - consolidate
To delete any duplicate points

- Tristrip
To generate individual triangles

- Point - Add normal

Now each point has either a normal facing in the direction of the prim normal, or facing away from the prim normal.

- Delete - By normal

If I could now delete by comparing the point normal with the primitive normal, I would be home free. :?

Cheers,

Jeroen

Sounds like you need to find the dot product between the point normal and the prim normal. That could get a little hairy unless you are happy with complex expressions. Not 100% sure it is doable don't have time to work it out right now… but knowing Houdini it probably is.