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Non-uniform b-splines

Posted by donkey on January 27, 2005 at 08:57:56:

Hi,

This question isn't really about subdivision, but maybe someone here still knows the answer. I'm also sorry if the question is stupid, since I'm pretty new to the whole thing.

I'm trying to define and draw non-uniform b-splines. And it works out rather fine. With Cox-deBoor recursion I can generate both uniform and non-uniform curves, closed or open. The problem comes with the parameter value.

If I have a knot-sequence U {0, 1, 2, .., n+4} and some control points P[0], P[1], .., P[n] for cubic spline-segments, I can't use parametervalues, u, where u U[n+1]. When I do, the resulting values goes towards 0 for every control point. The visual result is for every set of knots and control points a curve that starts and ends in origo.

Is it supposed to be like this, or am I doing something terribly wrong (perhaps I've not implemented the recursion algorithm correctly)?

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