Example of carving/flattening terrain under roadways

Here is the original elevation mesh, from 10m DEM which has been resampled at 3m, to provide more resolution for smoother terrain modification:

If one naively draped roads as geometry, even with an offset above the ground, then there are problems with the ground and roads intersecting each other, both geometry and z-buffer issues:

One approach, implemented in VTBuilder, is to "carve" the roadways into the elevation grid.  There are many ways to do this, but a simple approach is to push the grid vertices up or down to lie at the expected height of the road:

Then when the roads are draped at runtime, they will have less intersection issues, and can be draped more closely with less space between them and the terrain:

There are a lot of areas for improvement.

• intersections should be handled
• more control over the road edge envelope
• more intelligent deformation that considers the actual mesh surface instead of just the heixels
• better estimation of the road's true elevation instead of the current assumption which uses terrain height at each road datapoint
• etc.