On 30 Aug 2000 10:14:04 -0400, Warp wrote:
>Ron Parker <ron### [at] povrayorg> wrote:
>: You missed a step.  After you finish all the surfaces, you have to make sure 
>: they're correctly oriented.  Even if it's just one surface, you have to 
>: make sure you haven't inverted it.
>
>  Well, this is an interesting question. How do you determine for a closed
>mesh surface, which side is inside and which one is outside?
>  What about open mesh surfaces?

Open mesh surfaces are impossible, but that's because the term "inside" has
no meaning for one.

For a closed mesh surface, fire a ray from outside the bounding box and check
the normal.

Some "well-behaved" "closed" surfaces will still fail; a 3-d projection of a
klein bottle, for example, would fail.  Those are the fault of the modeler
and shouldn't concern us.

-- 
Ron Parker   http://www2.fwi.com/~parkerr/traces.html
My opinions.  Mine.  Not anyone else's.

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