Ron Parker wrote in message <36e3d8c8.0@news.povray.org>...
>On Sun, 07 Mar 1999 20:05:31 -0800, Ken <tyl### [at] pacbellnet> wrote:
>>On a side note to this thread I have always assumed from what is specified
>>in the docs that mesh objects are not allowed in csg operations.
>
>There are indeed two reasons a mesh can't currently be used in an
>intersection.  One is that they have no inside: the "am I inside"
>function for meshes always says "no."  The other is that they don't
>always return all intersections when asked.  What we're discussing
>is making those two statements no longer true.  What you've found
>must be a fluke.  It's been done before, in POV 2.2 with heightfields
>which at that time didn't have an inside either.  But I wouldn't
>count on it working from all angles.

I've found that doing what Ken has done usually works. You can usually use
differences to chop bits off meshes. If you try to reverse the difference,
take the mesh from the sphere, it doesn't quite work though. The mesh
appears as an infinitely thin surface (which makes sense I guess) and
appears to behave as such in CSGs.

On the topic in general, I would think the method of using the normals to
determine the "inside" was more useful as this way open meshes could also be
used. I still have a little trouble picturing how this would work exactly
though!

Regards
Gordon

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