On Fri, 8 Mar 2002 14:25:40 -0800, "=Bob=" <bob### [at] threestrandscom>
wrote:

>I'm afraid I just don't have the background to
>understand this yet. But I have need to know
>the angles for x,y and z of a tangent to a sphere
>that has been rotated on all axes. From what I
>have read, quaternions are the answer to this.
>Could someone point me to a way to implement
>this in Pov? Maybe someone has already made
>a set of macros?

Do it the POV way. Compute the transformation that would transform a
unit sphere into your sphere, then take the point you want to find the
tangent at, inverse-transform it to the unit sphere, find the normal
at that point (for a sphere it's easy -- vnormalize(point) :)) and
transform that normal back to your sphere. And the tangent is easy
when you have the normal.

Hope I didn't mess this up.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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