After swapping axis (because I forgot that OpenGL uses Y+ as up, I had to change the way I'm selecting where to place the road.
Now, I'm calculating the tangent at each point (the cyan lines). It gives a constant result that could be linkes to make a neat circuit.
@Ronflaix ooh, are these made of circular arcs, or…?
@Ronflaix haven't heard of those before, glad i asked!
@notwa You maybe want to check those blogposts : http://www.ryanjuckett.com/programming/biarc-interpolation/ and https://www.redblobgames.com/articles/curved-paths/
@Ronflaix is this for a racing game? do you think continuity at the joins will be an issue?
@notwa Yeah, it is for a racing game. For the continuity, alas I don't know yet. It seems pretty okay for now, I'll see later if it really gets in the way.
@notwa Yep, I'm using biarc interpolation for each segment.