# NURBS Range

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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.

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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.

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Quote:
 Original post by dinaharcheryDoes 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.

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Thank you for the response.

At least I know that it truly is difficult and not so much that I don't know what I am doing.

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Sounds like you want trimmed nurbs surfaces. Not the easiest thing to implement, but nice when you get them working....

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Yes,

NURBS Surface Trimming is exactly what I want. Thank you for the paper link.

I see what you mean - this is not an easy feat.

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