toSubD does not inherent CP structure with Deg 3 surfaces

ToSubD does not turn NURBS surface control points into SubD control points with Degree 3 NURBS surfaces. It does work above and below deg 3?!
Rhino Version 7 SR13

any suggestions?

I am seeing the same thing here- Looks buggy to me. I’ll write it up-

1 Like

Hm… that does seem incorrect - if the surface is not flat it seems to get it right. For now, ExtractControlPolygon then ToSubD the resulting mesh.


top… thx

I do not agree, same as in TSpline, has always been this way !
Srf(rigid flat) rule Degree3 / UV = CP 4 = SubD 1 Face,
Srf(rigid flat) rule Degree3 / UV = CP 5 = SubD 4 Faces
ect …
Base for SubD is allways degree3 and other than degree3 must by internally converted.
Accordingly it leads to the other topology.

but it works in former versions like shown in Phil Cook`s tutorial

Throw a few seconds here

Exception forms when the surface is curvy,
At the beginning and end the faces are divided.

from the docs:


Turns NURBS surface control points into SubD control points.
Use this option if you are doing “Class A” modeling and need to join separate SubDs into a single SubD.


The output SubD has the best fit to the input NURBS surface. Extra faces might be inserted.

Yeeh Srf with uv rigid is enough to raise one CP to mimicron and it works

Hmm with flat surface does this make sense ?