Spline type

Does anyone know what type of spline SW creates when you import xyz points from a text file? (B spline, Wilson fowler or some other?) I'm using 2006-sp5 Thanks in advance

Reply to
tjones2
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Hi there,

It will be a B-spline. I've written a macro long time ago to see the control polygon (SW2003) and as a side effect I've found a few things.

SW is not going to create true NURBS (weights other than 1), unless you convert analytic geometry (like an ellipse) to a spline. This is the only time I could force SW to give me something other than ordinary B-splines. They are always order 4 (degree 3) B-splines, the knot vector normalised, looks like this (0,0,0,0, .............1,1,1,1). For this reason they are also non-periodic. I guess this is to help data exchange. However, it is possible to create splines using API calls, in which case you are not restricted to cubics. You can do quintic, or anything you like and weights differing from 1 and make periodic splines. I didn't succeed creating closed curves, like a circle as a NURBS curve, but I could connect a spline and an arc as a NURBS curve as an exercise.

Also, after SW introduced curvature continuity and tensioning at the vertices, I could see that they are not actually making NURBS, but inserting an extra segment to the control polygon. It is pretty obvious now, but it was interesting to see back then.

I hope this helps.

Best Regards Attila

Reply to
bertok

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