In other words, if you want to extract curves, do it on a real 3D solid.

Extractisoline=surfextractcurve I already tried that command but it's giving me random lines on surface, i need isolines precisely as shown as on model or at least their intersection points, in anyway i can't snap of this isolines this is the real problem! Nevertheless thank you very much for your respond Vladimir

Cheers

I'm struggling since 3 years about that issue, maybe someone can help about it;

As you can see down below i have kind of vortex shape (surface) and would like to extract u and v isolines as polyline or spline for that extractisoline command just giving random splines, xedges command giving only top and bottom circles, if i convert that shape into mesh it's giving distorted mesh body, i can't also snap intersection of isolines to drawing with 3dpoly, i have no idea left can someone tell me what can i do more?

I just need exact position of isolines itself or intersection points.

Note: I found that script many years ago but won't work either!
Script:https://adndevblog.typepad.com/autocad/2014/03/extracting-isolines-from-surface.html

Thank you and Best Regards