Splitting curve at polar angle?

I’m not even sure I understand my problem.

My goal is to take an arbitrary closed curve, create two different offsets at different distances, and join parts of each offset into a closed exterior curve based on angles from the center. Like this:


In that example I have an interior ellipse, and two outside offsets that are trimmed at two angles, and then linked with a line.

In grasshopper, I’ve gotten as far as identifying the intersection points:


…but I’m stuck on trimming the curves. Worse, I’m second guessing whether this is even the right approach to the problem.

Should I be doing something like dividing the curve into 720 segments and offsetting the points by different amounts depending on whether they’re inside or outside the dividing angle? Is there a more elegant way?

two-offsets.gh (12.8 KB)

Like this? I see that you wanted just the boundary.

two-offsets-c.gh (13.9 KB)

Yes. Like that. I’m not sure whether to thank you or go weep, since I wrestled with that for a couple of hours.

Thank you!

I would do something like this.

PolarCutEllipse.gh (12.7 KB)

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and this

two-offsets2.gh (13.8 KB)

other solution

ellipse region.gh (16.4 KB)

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