Bad NURBS, bad!!!

[kiwi]

Does anyone know wy a scrip building a nurb suface with "CreateNurbsSurface()" and "NurbsSetPt3D()" (on the right V and U order) give me a surface smaller than the same points building a 3D poly. A bit like if the surface was build by control instead of interpolation...

Is any other nurb function that will create the exact surface describe by my points?

[kiwi]

quote:

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Originally posted by kiwi:

Does anyone know why a scrip building a nurb suface with "CreateNurbsSurface()" and "NurbsSetPt3D()" (on the right V and U order) give me a surface smaller than the same points building a 3D poly. A bit like if the surface was build by control instead of interpolation...

Is any other nurb function that will create the exact surface describe by my points?

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[Cloud Hidden]

I listed something that might be comparable in this thread... http://techboard.nemetschek.net/ubb/ultimatebb.php?ubb=get_topic;f=21;t=000216

Andrew Bell provided me with an answer in the VS mailing list:

Nurbs have an additional set of parameters not shown in the OI palette:

the knot values. Explaining exactly how they work requires showing some

reasonably complex mathematical expressions, so I'll just tell you the

code you need:

NurbsSetKnot(h1, 0, 3, 0.5);

NurbsSetKnot(h1, 0, 4, 0.5);

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I don't know if that gives any insights, but it tells me that these are complex beasts whose complexity is never fully visible. So when you're trying to replicate something, you're doing it without seeing all the information used by the nurbs.

[kiwi]

Interesting! after u,v, index,weight and degres, we have knots... and this time I couldn't find any reference on the pdf's other than the short descriptions on the related functions, and the exemple about the "cos surface".

Since, I script each "u" curve and loof them: works not so bad, but don't give a great control over the shape. Will study this Knots: any idea where find more info about how they react to math and trigo?

Thanks,

[Cloud Hidden]

>any idea where find more info about how they react to math and trigo?

Sorry, no. I'm at the limits of my understanding of it. I usually just repeat the question here, on the VS mail list, and in email to NNA and hope that Andrew comes to my rescue yet again!

[kiwi]

No luck on this one... I just get a mail explaining that NNA don't give support to custumers out of the USA (due to contract with distributors), at list I have he board!.

Thanks,