Wasn't it Mike Williams who wrote:
>Wasn't it Shishberg who wrote:
>>"Skip Talbot" <ski### [at] aol com> wrote:
>>> Is there a built in function that I'm overlooking that would allow me to
>>> compute a normal and tangent vector to a given point on a spline? I saw
>>> that Chris Colefax's spline macro can do this but is there something I can
>>> use with POV's built in splines? I'm looking at approximating the vectors
>>> by using adjacent points, but I was hoping there might be something a little
>>> more accurate.
>>>
>>> Skip
>>
>>Would official support for this be too difficult? It would definitely extend
>>the usefulness of built-in splines.
>
>I somehow seem to have missed the beginning of this thread, so apologies
>if this has been said already.
>
>To find the normal you can do something like
>
>#macro SplineNormal(Spline,C)
> vnormalize(Spline(C+0.00001)-Spline(C-0.00001))
>#end
>
>Finding the normals is a bit trickier because there are an infinite
>number of normal vectors to a spline at any point.
>
Oops. Replace the first two occurrences of "normal" in the above by
"tangent".
--
Mike Williams
Gentleman of Leisure
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