Hi,
Thanks again for your help. 
It did turn out I do have a ‘preference’ plane 
.
What I would like to get is the vector - perpendicular to the line - which runs in the ‘most vertical’ direction possible.
I tried to do this by retrieving the highest point of the circle, after which I can draw a line/vector. Unfortunately this ‘finding highest point’ is quite a slow component (example is only with 4 lines, but in the end it will be lots more…).
Besides this goes not correctly for horizontal lines.
Do you have an suggestion how you can draw a vector - perpendicular to the line - which runs in the most vertical direction possible?
Something like closest vector to vertical ?
2021-11-19 Find Vector perpendicular to line_re_RE.gh (9.7 KB)
Thanks again!