On Wed, 11 Aug 1999 22:30:39 +0200, ingo wrote:
>Trying to find a, unit long) vector parrallel to the intersection line of two
>planes, and in an attempt to understand vcross, I did the following:
>
>take 3 points: A, B, C.
>N1= vnormalize(A-B)
>N2= vnormalize(A-C)
>Nx is the normal of a plane
>
>L= vnormalize(vcross(N1,N2))
>
>Is L the vector I'm looking for?
>If not, how do I find the vector, and what is the meaning of vcross?

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.  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.

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.

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