Terragen is a scenery-generation package for Windows and the Mac, aimed at producing photorealistic landscape images and animations (http://www.planetside.co.uk/terragen/). It's easy to use, and a beautiful scene can be generated in a few minutes.
Figure 27-3. Class diagrams for Terra3D
Some examples are at http://www.planetside.co.uk/terragen/images.shtml and http://www.planetside.co.uk/terragen/gallery/gallerymain.php. Terragen is currently free for personal, noncommercial use, though there are some restrictions on the size and resolution of the scenes that can be built.
A terrain can be created in Terragen using fractals (I talked about fractal terrains in the last chapter), by painting the shape of the landscape, or as a combination of the two. Terragen supports powerful surface and color maps for decorating the landscape, water effects, clouds, atmospheric elements, lighting, and shadows.
Terragen can import and export a wide range of file formats through the use of plug-ins. For example, the Firmament plug-in allows Terragen to read BMPs, STMs, POV-RAY height fields, and U.S. Geological Survey (USGS) DEM (digital elevation model) and spatial data transfer standard (SDTS) files. The For Export Only (FEO) plug-in permits exports to BMP, DXF, OBJ, and RIB files.
My approach requires that Terragen exports its terrain to a Wavefront OBJ file, so the FEO plug-in must be installed ...