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NURBS Range

Started by dinaharchery Nov 24, 2008 at 4:37 PM 4 replies 1.5k views

Original Post

Nov 24, 2008 at 4:37 PM

Hello all, Thanks for all the help in the past, it has been most helpful. I am trying to learn the mathematics behind NonUniform Rational B-Splines and have a question that I hope someone can help me with. I have a cylinder shape that has been created from a NURBS function and two circles - one on each "end" of the cylinder. What I would like to do is "slice" the NURBS surface function such that the surface/cylinder is only rendered between the two circular "slices". I am hoping that this is just a simple problem that I am overlooking - any help would be great :). Once again, thanks.

dinaharchery

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dinaharchery

Dec 1, 2008 at 2:20 PM

Maybe I am approaching this all wrong.

Does anyone know of any good algorithms for NURBS surface point inversion? Maybe I could store the points that mark the cut off of the surface as a set of [u,v] values and just generate data within that range?

Any ideas?

Thank you.

swiftcoder

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swiftcoder

Dec 1, 2008 at 2:33 PM

Quote:
Original post by dinaharchery
Does anyone know of any good algorithms for NURBS surface point inversion? Maybe I could store the points that mark the cut off of the surface as a set of [u,v] values and just generate data within that range?

NURBS inversion is extremely difficult: in essence you have to invert the entire NURBS equation, and even then you must eveluate the entire surface for each inversion.

You can approximate inversion by storing the resulting mesh, along with the original u, v coordinate at each point. Then you perform intersection against the mesh, and bilinearly interpolate the u, v coordinates to find the approximate position in u, v space.

If all you want to do is clip against two circles, your best bet would probably be to perform CSG against the final mesh.