On 2022-05-26 10:17 (-4), Tor Olav Kristensen wrote:
> 
> But I'm now wondering if the original poster used another spline type in the
> other tool. The spline type in the POV-Ray code is "b_spline". But I've not been
> able to find out what spline type that is supposed to be. I very much doubt that
> it is the B-splines described here:
> 
> https://en.wikipedia.org/wiki/B-spline
> 
> Perhaps the b stands for Bezier (?) Maybe someone can verify this...

POV-Ray's b_spline is indeed a 3rd degree B-spline.  I verified this a
few years ago by plotting points derived by de Boor's algorithm against
a POV-Ray b_spline.  I have a very poor understanding of what is going
on mathematically, but I do know that b_spline is not a Bezier curve.

I found the Wikipedia article quite confusing, especially since all of
the illustrations have the curves intersecting the endpoints, yet de
Boor's algorithm, which the article links to, does not produce this
result.  I know that Bezier curves are related to B-splines, but I
haven't figured out how.

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