Looking for more TDFTerrainFileHeader/TerrainHeaderStart information

Is there more information somewhere on the layout of the fields referred to in the terrain header (TDFTerrainFileHeader/TerrainHeaderStart) like 'land cover', 'land class', 'water class', 'elevation' and 'main terrain data' ?I haven't found anything in the docs so far.Basically I am trying to figure out where the terrain type/texture references are stored that aren't defined as VTP data. For example like in the middle of the African Sahara desert, where there is nothing but repeating desert texture. I assume there is some basic texture layer for the entire world defined somewhere !?Thanks,Matthias