I used to work for Kinetix, a division of Autodesk as a programmer on the NURBS (Non-Uniform Rational B-Spline) modeling team. We were working on 3D Studio MAX which is a high end rendering system used for numerous films, television programs and commercials. As part of this work I needed to write a piece of code to test the API for NURBS lines and to add a little interest I wrote an IGC file importer to provide data for testing. This plugin should ship in source form with 3D Studio MAX R3. If for some reason it doesn't I'll try to get permission to post my new and updated version of the plugin.
For the Terrain data I used the 1:250,000 DEM data from the USGS. The data is freely downloadable. I converted the DEM data to TGA image files and then used the images with the Displace Modifier of 3D Studio MAX. If I ever get the free time I'm hoping to write a plugin for 3D Studio MAX that does DEM data directly tessellated it adaptively for production rendering.
This is certainly NOT the only way to do this. As was mentioned on rec.aviation.soaring there are numerous public domain rendering products, POVRay for example, that could be used to produce similar results. I just happened to have 3D Studio MAX available. It is my sincere hope that now that, the computer technology is present to do this sort of work, a grass roots effort may spring up to bring this sort of capability to any soaring pilot with a recent generation computer.
This is an example. This was a flight flown by Ray Lynsky from Ely Nevada in 1999.