"Gilles Tran" <tra### [at] inapginrafr> wrote in message
news:40c05c9e$1@news.povray.org...
>
> There are several issues with meshes in POV-Ray and this is one of them...
> and not the worst. At least black triangles can be photoshoped away.
> Subdividing is a solution but then it's not always possible to keep the uv
> vectors (Cinema 4D can do that but it's not exactly free). Christophe
> Bouffartigue once made a patch that seemed to fix this problem.
>

Ahhh... yes...  I did some Googling and came across this discussion from 2
years ago:

http://news.povray.org/povray.beta-test/thread/%3C3cf448cd@news.povray.org%3E/

I haven't tried it in MegaPov 1.0, but since it was a complete rewrite using
the 3.5 source, it's probably quite likely that the patch isn't there.

> Here are other issues you will meet at one time or another:
>
> - using high radiosity settings on multi-layered, semi-transparent meshes
> (such as hair) tend to darken them, sometimes turning the texture into
pure
> black. I never found a solution for this.

Yes, I've come across that.  I thought it was something stupid that I was
doing, but eventually my scenes get so complex that I have to turn down
radiosity settings anyway.  Well, that, and I spend a lot of time doing
outdoors scenes, which generally don't need much radiosity.

>
> - under certain lighting conditions, interactions between parts of the
mesh
> give ugly results: lighting artifacts start shining through the edges of
the
> triangles (nice cracking effect) or in other places. Particularly, I have
> ongoing problems with the eyebrows and lashes when used with certain hair
> models in Millenium figures. I sometimes use uvmapper to remove eyebrows
and
> lashes, which fixes it but isn't a good solution for close-ups. This is
why
> the kid in the "Reach of the stars" picture is seen from behind...
>
> -in Pov-Ray 3.5 using meshes and reflections can sometimes end up in an
> infinite loop (a real plague when I was working on the WTC memorial
> project). This seems to be fixed in 3.6 though.
>

I haven't come across those other issues, but thanks or mentioning them. It
will probably save me hours of trouble-shooting in the future.

I really hope that at some point someone can address the "smooth triangle
artifact" problem.  Now that I'm aware of it, I've noticed that it pops up
all over the place in other people's images.  As meshes become more and more
prevalent in POV-Ray pictures (which seems to be the trend for many of us),
this issue will probably become more of an annoyance.

To avoid problems that I've encountered with normals on CSG surfaces, I
generally try to use iso-surfaces when I can.  At the risk of sounding like
a complete buffoon, I have to ask if anyone has ever tried converting smooth
triangle meshes to bi-cubic patches?  It would certainly take care of this
problem, but my guess is that render times would go through the roof, and it
might produce some other problems as well.  But we've certainly seen
utilities that do the opposite (e.g. hamapatch).  It's easy for me to deal
in the theoretical, since I have very little idea of how this stuff actually
works.

-- 
Jeremy
www.beantoad.com

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