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How to reconstruct a B-spline surface's 4 sides to 4 B-spline curves?

Duplicate curve tool in Autodesk Alias

ps: It should be similar to Autodesk Alias's Duplicate Curve Tool, where you can select any U/V on a surface and rebuild a degree 3 B-spline curve. I don't know what's the algorithm behind.

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June Wang
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  • not my cup of tea but from my point of view you have 2 options: 1. sample the circumference points and [convert to B-Spline control points](https://stackoverflow.com/a/22582447/2521214) here example [of converting sampled points into bezier polyline](https://stackoverflow.com/a/61659245/2521214) 2. convert surface coefficients into curve coefficients. So set one of the parameter to zero or one and algebraicaly transform the hermit surface polynomials matrix into curve polynomials. never done that as I do not use splines I am more used to interpolation cubics (Catmul-rom) – Spektre May 22 '20 at 07:17

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The 4 boundary curves of a B-spline surface can be constructed easily as B-spline curves by using the first/last row or column of control points and corresponding degree and knot vectors. For example, the boundary curve in u direction at v=0.0 is a B-spline curve constructed using degree and knot vector in u direction and the first row of control points.

fang
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  • I suspected as much but was not sure if some additional computation is needed or not (+1 for clarification for me :) ) – Spektre May 23 '20 at 06:22
  • Please check out this question and provide your answer if you can. Thanks. stackoverflow.com/q/61988118/9887326 – June Wang May 24 '20 at 17:27