Terrain Editing
From Mod Wiki
Making a Terrain Model
EditWorld's Terrain Editor
MegaBuild
MegaBuild is a small application designed to ease the MegaTexture compile process. It includes options for MegaGen (to render the raw texture tiles), Renderlight (to bake lighting info into the tiles) and MakeMegaTexture (which compiles the tiles into a compressed .mega file). It's a one-stop shop for compiling MegaTextures.
For a full explanation, see MegaBuild.
STUFF System
The STUFF System is a quick and easy way of distributing thousands of models across a terrain. It is mainly used for adding grass, plants, small shrubs, stones and twigs on top of the MegaTexture.
For a full explanation, see STUFF System.