ShrinkTrimmedSrf not shrinking

I’ve got a trimmed surface here that doesn’t want to shrink like it should. I don’t need it fixed, just sending along for evaluating why…

problem surface.3dm (135.3 KB)

Observatioon: ShrinkTrimmedSrfToEdge works as expected.

Got that, thanks.

RH-75890 ShrinkTrimmedSrf fails


The “why” is that the surface is already shrunk.
ShrinkTrimmedSrf takes place in 2D parameter space. If you run CreateUVCurves you can see the surface is already shrunk to near the trim curves.

Untrim the surface and run List and look at the knot list.
The 2d spacing of the U Knots on the part of the surface that is outside of the trim boundary is less than 1/1000 of the spacing of the part inside the trim boundary. Its as if 2 surfaces with enormously different knot spacing were merged together.