Ron Parker heeft geschreven in bericht <37b1df4f@news.povray.org>...
>Where are A, B, and C?
>If N1 and N2 are the normals of the planes, then L is indeed the vector you're
>looking for.

In my case three points on a bicubic_patch, and N1, N2 are the normals of the
planes.

>To find the normal of a plane given three noncollinear points
>A, B, C on the plane, you'd use vnormalize(vcross(B-A,C-A)).  Repeat for three
>points in the other plane.  You can leave off the vnormalize in this case
>because you'll be normalizing your final result.


And this bit goes into my "knowledgebase".

>vcross is the vector cross-product, which is a vector perpendicular to both of
>the two given vectors and with a length equal to twice the area of the triangle
>between the two vectors.

The docs say something similar, but reading it and understanding it are two
things.

Thanks Ron,

ingo
--
Met dank aan de muze met het glazen oog.

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