Dan Connelly <djc### [at] yahoocom> wrote:
> As is often the case, my understanding was flawed.... there's no way to define a
mesh which is a hole in an infinite solid without CSG.  So a closed mesh really is
unambiguous, assuming no numerical issues.

  Well, I don't really know what you mean by "ambiguous".

  An open mesh with a given inside_vector is completely unambiguous in its
behavior as a solid (in CSG). Its behavior may be slightly counter-intuitive
in that part of the "inside" of the mesh will extend to infinity, but this
no different from how eg. a plane works: One side of the plane is considered
the "inside", and this inside extends to infinity.

  To understand how this works, the simplest case would be eg. a mesh with
one single triangle. Let's say this triangle is on the xz-plane (with the
y coordinates of the vertices being all 0), and an "inside_vector y".
Basically this mesh now forms an infinite triangular prism solid (which
extends from y=0 towards the negative y axis direction). It's just that
this "prism" as only the "end cap" (the triangle in question) but no
visible "walls". However, in CSG it will behave like it had them.

  (Disclaimer: No, I haven't actually tested it actually works like this.
However, knowing the algorithm used for the insideness test, I can't think
how it could work in any other way.)

-- 
                                                          - Warp

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