_ExtractSubCrv doesn't work sometimes

Rhino Rhino for Windows
1

Hi all,
See the attached file. _ExtractSubCrv doesn’t work on that curve. If I explode it and rejoin it does work.
Is this a bug?

gr, Tobias

crv.3dm (201.7 KB)

2

Hi Tobias- yeah… this is listed as a single NURBS curve (What command) and not a polycurve. SimplifyCrv will restore it as a polycurve with identifiable sub curves…

It is a little weird from the users perspective that this happens - you can make a NURBS curve from the simplified curve again by nudging a control point and then nudging it back again - the shape will be identical but it will no longer be a polycurve. There is talk, from time to time, about making this be a little more intuitive and consistent…

-Pascal

3

So this is intended behavior??
The curve is created by duplicating a polysurface border. The source polysurface was created as a simple straight shape and fillet edges. So why the extracted border should be a single NURBS curve?

4

Hi Tobias - I just tested this and here I get a polycurve…

-Pascal

5

Yeah, that’s what I usually get too but sometimes not. Unfortunately I don’t have the original polysurface anymore. Next time I come across this I’ll try to include the source object.

thanks, Tobias

6

Pascal, let’s say I want a single NURBS curve… would it be possible to merge a polycurve into a single NURBS curve while maintaining the exact shape?

gr, Tobias

7

Hi Tobias - the quick way to do this is to turn on control points for the polycurve, select one, and nudge it (Nudge key) and then Nudge it back to where it was.

-Pascal

8

Yeah that works… thanks.
But like you said, the whole thing is not exactly intuitive…

gr, Tobias

9

Yeah - I just had this and was very confused. Thought it might have been something to do with grouping or something. Explode and Join made it okay.

extractsubcrv.3dm (48.0 KB)