Why doesn't a negative Offset work on this curve?

I can offset this curve in both directions in Rhino. Why Can’t I offset it in Grasshopper with a negative value?

190417 Offset curve.gh (8.8 KB)

It seems like flipping the curve solves it (I’d like to avoid flipping the curve though) so I’m wondering if it could be related to this topic:

You need to clean your curve.
Near world 0,0,0 your curve has a segment with almost 0 length.
Remove it and offset works good.

Interesting, good spotted! But then why does it not give problems in Rhino?

“why”… no idea.
Anyway those are different funcions.
On rhino you always click one specific point to input the side of the offset and then that point location is also used for the creation of the offset itself.
On grasshopper you just give the value.

Never equate a Rhino command with a Grasshopper one. The name may be similar but the two usually don’t have the same features. Rhino typically has lots of built in checks and fixes. Grasshopper is more deconstructed and it is up to the user to decide how to determine what the fix is, because it is like scripting.

Hi Siemen - it doesn’t give you any problems with offset but it might (probably will) cause problems if you start building surfaces from this curve (e.g. exporting an extrusion to DXF). If you ask me, this curve should be flagged as bad by Rhino and I have added this case to bug report RH-51813.