Wasn't it Shishberg who wrote:
>"Skip Talbot" <ski### [at] aolcom> 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.

-- 
Mike Williams
Gentleman of Leisure

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