Whatever Terragen can animate, Terranim lets you control it. Camera Path Editor - animation script generator by Sean O'Malley . Packed full of all sorts of goodies, including a 'Vehicle Cam', cloud and sun movement, handy 'global change' features and a FOV calculator, to name but a few. You may find some of the following links useful if you want to use external data within Terragen. Remember, Terragen can import raw binary data as terrain.
Most paint programs can export images in raw format.
3DEM - program for the display and manipulation of DEM files. Now exports Terragen Terrain files. It now supports Terragen Terrain files . DEM2TGA - small utility for converting USGS DEM files to TGA images. TopoWeb - useful resource.