How does one draw on Atlas terrain?

I'd like to be able to draw simple line primitives on top of the Atlas terrain but have them actually drape over the terrain mesh. Any suggestions on where to look for pointers, examples, etc. for this? I'm thinking something like how google earth can draw lat/lon lines and other features on the ground.

Specifically I'd like to read in point files that define boundaries, lat/lon lines and such and draw them. A lot in fact like how Google Earth can overlay things onto terrain.