Cliff Bowman wrote:
> 

> I think what I'm going to ahve to do is write a "face preview"
> facility in OBJuvPOV I think. So that I can *see* what the program's
> encountering to help me evaluate which tack might work (I'm not good
> at math - I've not the first idea how to work out if a face is planar
> given just the verteces - unless they happen to lie along one of the
> axes, of course!).

Any three points define a plane.  Derive an equation of that plane from
the vertices, and test the other points to see whether they lie on that
plane.  Actually, you should expect a little deviation from the plane on
account of finite precision, so test whether the point is within some
small distance epsilon of the plane.

-- 
Mark Gordon
mtg### [at] povrayorg

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