Hello, Looking for help in regards to a plate with hole where the user would like to obtain the control points and the weights. The problem with rhino is if i look at the out curve of the surface you can see that the control point creating the circle has a weight of 0.707 (as it should) [image] w…

[image] user90: How did you do this? [image] Split the arc in the middle EdgeSrf with red + magenta EdgeSrf with cyan + magenta (or mirror across diagonal) MergeSrf the two adjacent edges Smooth=No Done. SingleSrfCrvs.3dm (29.4 KB)

check out https://wiki.mcneel.com/rhino/nurbs [image] Non-uniform rational B-spline Non-uniform rational basis spline (NURBS) is a mathematical model using basis splines (B-splines) that is commonly used in computer graphics for representing curves and surfaces. It offers great flexibili…

Hello- knot values must be increasing but need not be positive. I am not sure what to make of the rest of your comment. -Pascal

Hi Tom, Thanks for your response. I’m not sure I completely understood this concept of boundary representation. How is it practically used in rhino?

[image] user90: Im trying to explain that when designing a surface with a hole as you can see Rhino creates control points which are wrong by definition of NURB surfaces. By definition of NURB surfaces and in order to obtain the correct figure when running a NURB surface routine all values of th…

From what I understand, the reason for the negative values of the knot vectors is because rhino must compensate for the fact that it is trying to create a curved surface from the convex side and not concave as is expected. If you look at the boundary curve you can see that the control point of the c…

I think maybe the OP is not understanding trimmed vs untrimmed surfaces?

[image] user90: the moment you try to do the same as a surface what does this mean, exactly? what process are you using to do this? -Pascal

[image] user90: From what I understand, the reason for the negative values of the knot vectors is because rhino must compensate for the fact that it is trying to create a curved surface from the convex side and not concave as is expected. Incorrect assumption. Negative parameter values are un…

Planarsrf Is there a different command that will not give a rectangular control point mesh

Hello- please see the Help files and level 1 and level2 training materials here - https://www.rhino3d.com/learn/?keyword=kind:%20rhino_win -Pascal

Nurb Surfaces, Control points and weights

Rhino Rhino for Windows

Tom_P October 21, 2021, 2:56pm 4

check out
https://wiki.mcneel.com/rhino/nurbs

there is a underlying nurbs-Surface and trim curves that define the visible / used part of the surface

see this info to understand the underlaying concept

kind regards -tom

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Nurb Surfaces, Control points and weights

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