How to split a mesh with a projected line and then shrink it?

Rhino Rhino for Windows
1

I created a mesh from grasshopper, converted to subD, and projected lines on it.

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And Now I want these projected lines to be the edges of the subD surface, so that I can shrink with the surface with those lines. Would it be better to work with Polysurface instead of SubD in this case?

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Any tips would be greatly appreciated!

And is there a way I can reduce/undivide/merge SubD and Polysurface faces? Like the feature that does opposite of “Subdivide SubD”.

Thanks!

2

Hello- no… what might work, though only partly, it may not match the outline exacly, is SplitMeshWithCurve until you have that triangle and then ToSubD.

-Pascal