I closing a bunch of curve pairs by connecting their open ends with line segments. However, there is this one case which fails; the joined curve consists of 5 vertices (see explode curve component) and as a result, the Boundary Surface fails outside the closed curve. [image] Boundary surface fail…

are the internalized curves two trimmed curves?

my feeling is there is something to do with the degrees of the input curves? since one is an offset of the first.

Looks like the offset flipped one of the curve domains: [image] E: even Fitcurve leaves behind a 5th vertex. With 4 curve segments, there should be 4 vertices (in this case). The problem is that there is an overlapping vertex. [image] E2: A rectangle has 5 vertices too when exploded, so nvm.

but a deconstruct brep gives you 4 vertices :smiley: i think when you explode a closed curve, it gives you the last vertex identical to the first one: you have n curves, and n+1 vertices as each curve has two end points. i think the issue is with the input curves, specifically with the second being …

or Pull Curve or Sweep [image] @Intuos Yeah. The seam of a closed curve is repeated in the vertices.

Interesting. How did you do the offset? Offsetting the outer curve in Grasshopper results in a correct solution. [image] Boundary surface offset.gh (4.7 KB)

Yes, it clearly is the curves that are the problem, that much I’ve figured as well.

[image] Volker Rakow: the curves It would be nice to know how the offset was created.

Sorry had to leave earlier. Here’s the file with the offset with an internalised curve. Notice that you can bake the curve to replicate the screencast I posted earlier. Boundary surface fails.gh (14.8 KB)

Boundary Surface fails to create the surface within the closed curve?

Grasshopper

Volker_Rakow (Volker Rakow) October 7, 2025, 4:44pm 13

or Pull Curve or Sweep

@Intuos Yeah. The seam of a closed curve is repeated in the vertices.

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Boundary Surface fails to create the surface within the closed curve?

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