SubD to Nurbs, limiting the amount of cvs a patch uses

Rhino SubD
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When converting SubD to Nurbs, is there anyway to have all the patches be a certain amounts of cv’s/isoparms that all line up

I know after conversion to Nurbs you can use the “Rebuild Surface” tool to change the amount of cv’s a surface uses, but then all the surfaces don’t attach together perfectly (all the cvs between patches aren’t lined up exactly and there are gaps between patches)

Also if there is no way to do this in Rhino, does anyone know of a program that will allow me to convert Subd to Nurbs where all the Nurbs are 4x4 patches that perfectly line up. Right now i’m importing nurbs from rhino to maya to make them a 4x4 cv grid and stitch them back up and its a bother

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no current way to do this at the moment other than manually rebuilding each patch and matching them all back together which is not necessarily practical or doable.

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Maybe with V9 _Fillsrf we can find a manual workaround to solve some heavy parts, what you think Kyle does it worth a try?

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That is a question for @dalelear or one of our other devs as to if it’s even possible…

that is way beyond my art schooling to answer… :wink:

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ToNURBS SubDOptions Faces=Unpaked will give you mostly degree 3 surfaces with 5x5 CVs. Around extraordinary vertices, the CV count needs to be increased to match the limit surface of the SubD, there is no way to represent the limit surface there with only 5 control points per original SubD Face.

You can reduce the extent of these extraordinary surfaces by SubDivide-ing your SubD first. Of course, that will result in many more surfaces overall.

If the Faces Packed option is used, regular grids of 4-valent faces will be merged into one large NURBS surface. It is exactly the same shape, just with the redundant CVs between faces merged together. This moves the CVs but not the isocurves, and in most cases the CVs will still align with the neighboring faces.

In both cases (extraordinary vertices and packed faces), using Rebuild or any other command to reduce the CV count will change the shape of the surface. I don’t know if this is acceptable for you. FillSrf could help you rebuild the faces around an extraordinary vertex, and control the tolerance at the edges, but I don’t think you’ll be able to get the CV rows to line up (there is no control over knot positions, and the resulting surface will be trimmed in many cases).

@Thomas_Phillips Do you have an example model or an image of something that doesn’t work for you in SubD’s ToNURBS, and how you would like it to look like? I don’t understand which options you are currently using, and what is the result you are after.