Although I haven't written a line of code in SimGear for draping, yet - I'm getting a pretty good idea on how it will work. I think we could speed up the OBJECT_STATIC_AGL using the envisioned draping code.

Currently, when a tile loads, it first gathers the type of objects in the tile. If there is a draped object, I plan on keeping raw btg data (nodes and triangles) around. I need the Geodetic nodes, unfortunately for proper draping, so I'm going to have to create a parallel node list Cartesian ->Geodetic. The triangles are all index based anyway, so we'll just refer to the Geodetic nodes when using these triangles.

A draped object's 2D bounding box will be used to quickly find the relevant triangles (using the geodetic nodes long/lat) that need to be considered, then I plan to use barycentric interpolation to find node heights at specific lat/long coordinates. This node will then be converted back to Cartesian space.

My development time is severely limited at the moment - I've been working on this more at work than at home

I hope to have a proof of concept ready in a couple months.

Here's the simgear repo I'll be checking into - It's at least up to data - just no changes, yet...

https://www.gitorious.org/~psadro/fg/psadros-simgear