Hello Rhino Forum,
I am doing an exercise from the rhino level 1 training guide.
I want to snap to the intersection of two yellow lines in the middle of the rectangle. Unfortunately, no matter what osnap mode I turn on, it won’t snap to the intersection.
I have noticed that the locations on the curved that I can snap to seem to be (a little) thicker yellow lines.
What am I doing wrong?
You’re doing nothing wrong. These lines running across the surface are isocurves, and not actual geometry. You can convert it into geometry if needed with _ExtractWireframe, then End and Intersect Osnaps should work
Yea, that worked, thank you very much! The part of the intenet where I can ask a technical question and usually get a good answer from someone I have never met before is extremely nice! 
Hello - Intersection OSnaps will find isocurve intersections if the selection is constrsined to the surface - this can happen automatically in a command that uses a surface as input, as in InsertKnot but you can force it with the OnSrf one-shot OSnap combined with Int.
-Pascal
Thank you very much for your recommendation @pascal. I wasn’t familiar with “OnSrf” and “one-shot Osnap” but it seems that snapping to ISO curve intersections works fine with only using “OnSrf”, no need to combine it with one-shot OSnap + Int.
