Chris Colefax wrote:
> 
> Ken <tyl### [at] pacbellnet> wrote:
> >  In the sample below we have an example of degenerate triangles. The
> > indented triangles are those that Pov reports as being degenerate.
> > When rendered as a union the degenerate warnings appear. When commented
> > out those warnings disappear. When rendered as a mesh however Pov fails
> > to report them as being degenerate. This has been true since the mesh
> > wrapper was added in Pov v3.0x. Why are they not being reported as
> > degenerate triangles when used in a mesh ?
> >
> > I have asked this before and have never received a response. Hopefully
> > someone has an idea now that I have provided an example to evaluate the
> > discrepancy with.
> 
> It would seem to be the simple fact that when parsing meshes POV-Ray ignores
> degenerate triangles completely, whereas in the union each triangle is
> parsed as an individual object and so degenerate cases do get reported (a
> possibly dubious theory arrived at by the fact that creating a mesh composed
> entirely of degenerate triangles simply reports "no triangles in mesh").

In essence then instead of warning the user to remove the degenerate triangles
pov simply handles it for you when meshes are used.
 
> I can only imagine the rationale is that meshes are generally outputted by a
> program (conversion or otherwise), and might very well contain many
> triangles that POV-Ray can't use (in which case warnings would simply be
> annoying, rather than useful).  Non-mesh triangles, on the other hand, would
> usually be entered by hand, and as such a degenerate triangle is more likely
> to be a genuine user mistake....perhaps?!

The one possible danger to this non reporting scenario would be scene debugging.
I have seen several macro's lately where triangles were created by whatever the
function of the macro was. If you make a mistake in your calculations and Pov
carefully removes your bad triangles for you it might be very difficult to figure
out why your shape is not being produced as you would expect it to. Good or bad
it is different and I thought it was worth mentioning.

-- 
Ken Tyler

See my 700+ Povray and 3D Rendering and Raytracing Links at:
http://home.pacbell.net/tylereng/index.html

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