Patch trim bug

Patch is incorrectly auto trimming a surface created using a simple set of curves. The curves are from a post by rob_bosnjak Curve network File with incorrectly trimmed surface from Patch attached.
Patch trim bug.3dm (255.2 KB)

Hi David - got that, thanks.


Hi David- here’s what I learned- the outer ‘obvious’ curve is pretty far (out of the tolerance used) from the patch surface in this case so Rhino does not use it to trim with. Patch uses the outermost curve that is within a tolerance of the patch surface to trim with - in this case that is the next curve in. So, it is working as designed, the real solution for the user is to trim by hand, or come up with some settings that bring the patch closer to that outer curve.


@Pascal That’s not the cause. Cause is related to the bottom curve being a polycurve with two segments and discontinuous curvature while the curve above is a single periodic curve.

The curve that is used for trimming (second from the bottom) is as far or further from the patch surface than the obvious bottom curve. I checked for both the example I posted above and for a 51x51 patch surface. So that is not the cause.

Properties for the bottom curve show it as a “Closed polycurve with 2 curve segments”. Curvature is discontinuous between the segments. Properties for the second curve show it a “Periodic NURBS curve”. I rebuilt the bottom curve as a single, periodic curve and Patch now auto trims using it.

Also, while I don’t think the auto trim part of Patch is working quite as most users would expected, it is not serious bug since the result is easy to correct.

I agree it is not the worst problem but I’d still like it to work better- I’ll poke at it some more - thanks.