How to open a closed curve

Grasshopper
#1

I have a closed curve and I want to extend it at the seam to make a α-like shape. Extend-crv doesn’t seem to work on closed curves.
Can I convert a closed curve to an open one?

#2

Without file, it’s a bit hard to know what s best for you.

is there a kink? only one? reparam the curve, discontinuity, shatter, extend.
no kink? reparam the curve, eval (with two value between 0 and 1), shatter, select cure the one you need (probably the longest one), extend.

#3

Pufferfish has an Open Curve component.

#4

Thinking about the problem in a different way, do you really need to make everything a singular closed curve?

You could just extend the ends points by taking a Perp Frame at the end (see attached script).

Extend close crv.gh (6.0 KB)

#5

Basic closed curve (no kinks), could be a circle. Must I split in two parts before I extend?

#6

You will want to open it first creating a gap to then over extend it.

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OpenCLosed.gh (7.2 KB)

2 Likes
#7

That’s clever but is it accurate? In this test it seems so, but will this work for other more complex curves?

Canvas at 17;00;33
Canvas at 17;00;331722×873 140 KB

#8

is it accurate

You open it 0.001 units. So it is going to be as accurate as anything else in Rhino since that is a typical document tolerance anyway.

1 Like
#9

Nice! I think I’ll stick to that then.
I was attempting (and failing) with a different method.
Maybe I can pick your brain on knots while you’re here…

Canvas at 17;21;37
Canvas at 17;21;371916×916 184 KB

Is there a method to create the knot parameters so that the generated curve follows the ellipse?