GeometryTemplate.MaterialMap

MDT description

This property gives the path and name of the .raw file that is used to specify the overall materials of the terrain, with numbers 0-15 (the top 4 bits of each byte are not used):

 0 Default
 1 Water
 2 Dry Grass
 3 Juicy Grass
 4 Dry Dirt
 5 Wet Dirt
 6 Mud
 7 "You are leaving the battlefield"
 8 Gravel
 9 Frozen Ground
10 Dry Sand
11 Wet Sand
12 Rock Surface
13 Sand Road
14 Wet Road
15 Paved Road

The heightmap file for the terrain is specified by the File property. The MaterialSize property specifies the dimensions of this image. TexBaseName sets the location of the actual high-resolution color textures.

Source and more details