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Eternal

Splitting and Tesselating NURBS Surfaces

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Even though my maths skills aren''t really up to it (just started with differential calculus at school), I''m currently experimenting with using NURBS Surfaces in my renderer. I have a few problems tho. My main problem is how to split a large set of control-points (say 66x66 points) into a number of smaller patches (4x4 points). So far I just took 4x4 controlpoints from my original set, so that all patches share controlpoints with the neighbouring patches on the edges. But how would I set up my knot-vectors ? The large surface currently has non-periodic and uniform knot-vectors (0,0,0,0,1/x,2/x,3/x,...,1,1,1,1), which isn''t too great, but if it makes things easier I can keep it like that. So, well, I actually have no clue if my approach even could work, but if it could work, I still have no real clue on how to set up my knot-vectors for the small patches. The second problem, where any help or links would be great aswell, is how to do non-linear tesselation of my patches. The general idea is to do something like what kronq described in this thread some months/almost a year ago.
quote:
Original post by kronq heres a pic of a fractionally tesselated Bezier patch with different tesselation at each edge. Each separate quad strip is in a shade of red, each triangle fan is in green. I''ll forego explaining it in detail because I think looking at the picture will give you a fair chance of deducing how its done, but here are the main points to keep in mind: - each edge has an odd number of vertices -- minimum 3 - each edge always has a point at 0.5, and all the other points on the edge are symmetrical on either side of the 0.5 point - as LOD increases, new points are added at 0.5 and move outward *----*----*----*----* *----*---***---*----* *---*---*-*-*---*---* - lets call the LODs for each edge u0, u1, v0, v1 -- the LOD for the center portion is (u0+u1)/2 x (v0+v1)/2 - if an edge LOD is different from the center LOD a triangle strip is used to make up the difference
This gives my a rough idea, but as the pic is not online anymore, I have problems figuring out how the tesselated surface should look in the end. If anyone has experience with this or has a link to some paper explaining this or a similar method in greater detail, some advice could really save me some trouble and time.

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