generate an infinite terrain

[vadrian]

I am trying to make a simple flight sim world, but this question applies to any "outdoors" VE.

How can I generate an "infinitely" expanding terrain?

I want the user to fly/move about the world and always have terrain in the distance. I don't care if the pattern repeats (i.e. tile a terrain) or if its unique (i.e. dynamic/random generation).

- adrian