What I recall is that the designer would model the profile of the terrain in the editor, the editor would then save a height map, the height map would be imported in Corel Bryce (or similar program) where it would be rendered several times with different textures, the images would then be opened in Photoshop (as several layers of one image) and artists would delete or masks part of them to create the desired look of the level. This would be exported as a single image and this image would be converted by our tool (grndsec?) that would try to match the original textures to some areas of the ground (as a sort of compression, the resulting image is smaller than using general lossless compression) and create *.gbi file.