Offset flip problem

Hi all,

can someone explain me why the offset curve is flipped.


flipped offset.3dm (151.4 KB)

Are all curves going in the same direction? Check using the Dir command.

yep

I checked everything and it was the same thought at first.

that is unfortunately one of rhinos most persistent bugs which occur in quite a few commands. when something changes direction going along several axis it flips due to lack of something like an up vector which the calculation could adhere to.

in this case you are in luck and the command slab will help you out. just copy the resulting edge and delete the rest if not needed.

Thanks for the info
This is a really stupid bug.

Is it though? A curve has no obvious outward facing normal direction (like a surface does). So some complex things need to happen to guess a direction at each location.

no it is thought…but the sentence is completly messed up.
It should be (maybe) … I was thinking the same thing (i guess).

Anyway i use offset on surface to avoid the offset flip thanks to your tip about normal direction.

But if i check the frame on the offseted curve before and after the location where the flip happen no flipped vectore is present.

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Hello - offsetting a curve is a planar operation - if the curve is planar then that can be used, else the CPlane is used. A true offset of a curve is a pipe surface of course, so some constraint needs to be used to get a curve.

-Pascal

Can you elaborate what you mean by that.

Well, just that, if you offset a line, say, with no other constraint, there is an infinite number of offsets possible, forming a cylinder around the line.

-Pascal