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?

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.

Pufferfish has an Open Curve component.

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)

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

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

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.