"Mesh Mongrel" <cor### [at] userssourceforgenet> wrote in message 
news:web.43586b5c748e45a8cfcbd10@news.povray.org...
> ... snip ...
> I get very strange results when I try this.  I end up with shadows in
> strange parts of my panels.

Bands of shadows can occur in the middle of a panel if the normals at the 
vertices are pointing in opposite directions.
When you do a cross product at the apex of a triangle that is facing towards 
you, you get two possible results.
One is a normal facing towards you, the other is a normal facing away from 
you. This depends on the sequence and direction of the vectors you specify 
with vcross.

Reading the help on the POV-ray coordinate system should give you a better 
understanding of this.

I find it helps to consider the corner of a triangle re-oriented so that one 
edge points in something like the direction of +x and the other points in 
something like the direction of  +y.
If you pass the vectors to vcross in that sequence, then the resulting 
vector will point in the direction of +z.

Chris B.

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