Offset curve on surface

offset.3dm (44.7 KB)
offset.gh (9.9 KB)

I want to make “offset crv on surface” both from center iso crv. but it’s not work one of two curve. it is postponed if I connect negative distance.

instead of negative you can flip the U curve before offset, see attached.

offset_sg.gh (5.5 KB)

It is perfect.
Thank you so much~^^