Project roads onto topography

I would like to project my closed road crv onto the surface below (topography), and then still be able to extrude them. The problem lies in the project command that i have been playing with. after projecting the roads they no longer create solid capped extrusions.

Any solution or other methods?

Example.3dm (2.1 MB)

if the resulted projected curve is not planar, cap doesn’t work. I think you can extrude the roads, make a boolean difference with the topography, then you can move the road a bit down and repeat the difference but the other way around.
Also you have self intersection curves here:

i have a couple questions

how did you find the intersecting curve?

I fixed the self intersecting curves. I tried that method but the boolean diff fails.

think another method would be to project only the buildings points to the surface then manually connect them. Ill update with results

SOLVED

Essentially I was trying to create a topography that had a road carved out.
The problem with this is usually GIS roads are not closed crv’s or just all kinds of messed up.

Workflow to do this.

Create or download your roads. _projecttocplane (delete input) > place topography below your roads > turn your roads into a crv outline however you have to do it > top view > turn your topo into a surface (meshtonurbs) > _project your roads onto the surface > _patch your new crv’s > delete all remaining curves > select all and _trim the unwanted surfaces > _extrudesrf your patch roads to the depth you want your road to be > extrude srf downwards your topogrphy to the depth you want it to be > _booleandifference.

The workaround was the patch command.

when I tried the extrusion it says it have self intersecting curves so, I choose the option Solid=no and I have the shaded view configured to always see naked edges in different color ( as you can see above, green edges are naked edges)
in the extrusion I look the verticar edges until I saw a green one ( naked edge)

you can use the tool _ShowEdges to see which edges are naked or non-manifold

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Can you use Lands design in Rhino?