Not sure exactly what you mean. Do you mean how to create 3D terrain in general? And I'm assuming this is for a game. If thats the case you'd need a 3D modeler such as 3D Studio Max or Milkshape or you can use a 3D landscape program such as Bryce 5 or Vue d'Esprit 4. You'll want to make sure your poly counts are fairly low though. However, all these programs will cost you some money (and in some cases ALOT of money). You can check out the link below for other 3D terrain software. I'm sure theres a few inexpensive or maybe even free programs out there but I can't seem to remember the names of those.

http://www.3dlinks.com/software_landscape.cfm

Hope this helps...

Jeremy DenHartog
CEO/Designer for X-Factor Studios
http://www.x-factorstudios.com

[edited by - X-Factor Studios on May 2, 2002 1:40:15 PM]

http://www.vterrain.org/

Use an API like Direct 3D or Open GL and specify the vertices that make up your triangles, and vary their heights based on an array.