hi @phileas.schulhof ,
It seems you got caught by the duplicate post patrol 
@Joseph_Oster is generous, but you have to be disciplined in your inquiry.
because the tutorial you’re following does not show to you what to do when your situation isn’t the same as in the tutorial 
long story short: you must account for trimmed vs untrimmed, hit vs no hit (when dealing with projections/mesh ray), luck, fate, Rhino’s mood, tolerance, your own mood and tolerance, Murphy’s law, and all that.
Try this:
Terrain From Contours.gh (20.3 KB)
