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.