Surface extend problems

why rhino surface extends have no problem

grasshopper uses surface extends method having problem?

It’s because it’s a trimmed surface in Rhino. Even the following C# code will give you the untrimmed surface regardless of any extensions, give it a go with your input:

private void RunScript(Surface surface, ref object A)
A = surface;

I’m not 100% sure with exactly how to solve this, but it will involve understanding how to maintain and manipulate surface trims within a BRep, Surface or Nurbs. I can only find trimming properties for BReps myself (e.g. Curves2D), but that’s where my knowledge ends.

Hope you can find someone on here that knows more, sorry I can’t help ; )