Grasshopper lines on mesh

hi, i made some mesh3
and i’d like to work with lines on mesh surface
More specifically, the lines in the attached photo …

it seems contoured lines and i dont know what to call these vertical lines.

anyone has idea how to extract lines?

I‘m sure, where you found the second picture you will find the answer to your question.

contoured one does not seem to be difficult. But How to make a vertical line?

Point charges from rising and falling points can be used, but I do not know how.

I just can repeat me. Where you got the picture from? How this lines were created?

05170 (21.6 KB)

and second one
Rheotomic_Surfaces (30.1 KB)