There is a question: how to create a 3D road network based on spatial curves? Here’s one way I came up with a multipipe: with multipipe, but I don’t know how to extract the edges, or is there a better way to fix it?
Curve joints don’t need to be rounded, chamfers can also be, as long as they can transition smoothly
EXTRACT MULTIPIPE OR SUBD LOOPEDGE.gh (33.3 KB)
From the pics, I assume you want the 2D outer edges, correct?
You can achieve that easily by connecting a brep (to preserve the smoothness) to your SubD and getting the shadow or even using Make2d
See attached
thanks, bro! But I want the 3D outer edges, I want to modeling 3d road or path from 3d centerline.
This is a joke, not a general solution, so I don’t mind if you laugh.
P.S. Slightly less funny? But I have no idea how to make a road surface from these white curves?
Thank you！It worked, but I found that the edges were not horizontal, and perhaps based on the multipipe was wrong。
If they were horizontal this would be easy 
Intersect with ‘XY’ plane and Boundary surface.
Maybe I’m misunderstanding the problem but @Joseph_Oster’s white curves, connected at each end with a line segment, then join curves to get a single Polyline curve for the whole thing should give you the road boundary in 3d you need.
Then you use Patch to get a Surface fitting said curves.
Next use Surface Split to split the patched Surface with the Boundary Curve.
Then get the resulting surface as your road surface.
