Extend Srf: lines strange

Doing an extend srf on edge A why appear strange lines?
offset srf_ lines strange.3dm (160.2 KB)

That’s one freaky bug! :grin:
I have of course no idea what’s going on, but it looks funny!


Is a bug that ,I hope, will be corrected as soon as possible: very annoying!

I don’t understand what you’re looking at, it seems to work fine here… ??
(I don’t see anything strange with the extension)

Mitch, you generate so many random lines when you make the extension of certain surfaces. It also happens by extending a truncated sphere …

OK, now I see this when the extension is not created because of a collision/self intersect…


Mitch, look this post in the section “Rhino for Windows”: Wish: command “extendSrf”.

Got that, thanks.



RH-39832 is fixed in the latest WIP

I notice a difficulty in extending a surface generated with XNurbs.
Towards the inside of the surface this is extended (but up to a certain point); towards the outside, however, the surface cannot be extended well.
Bug or limit?
(Rhino 7.3)
extend srf non ok.3dm (179.7 KB)

This surface appears to be a setback corner, therefore making it a derivation of other derived surfaces. If so, a more practical modeling approach may be to modify the other surfaces, then recreate this one.


Looks like typical behavior of a higher degree surface. The surface is degree 5 in both directions. The higher the degree of a curve or surface the more likely it will twist and turn severely when extended. That is how the math works.

Attached is a file where I copied the degree 5 surface, untrimmed it and used ChangeDegree to create a degree 3 version. The deviation of the degree 3 surface from the original degree 5 surface is small, and would be less if I had used Rebuild with additional control points. Then I extended both the untrimmed degree 5 surface and the degree 3 surface used ExtendSrf with “distance” of 2.
Extend degrees.3dm (1.5 MB)

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