You dont need the terrain to be just one "Terrain". If you mess with B3d you will find that you can load lots ot terrains and stick them next to each other.
So... imagine you want "Infinte Terrain" al la IGI, you have the real terrain as (say) the middle of a group. As the player leaves the middle terrain you are already showing the comp generated/standard terrain, but you the generate the one that the player is walking towards as well (Well the three they are walking towards, but lets not complicate it). Then as they reach the edge of the next terrain you .... etc.
Obviously you can do it differantly/better by (say) having a low res terrain "Under" the ones you are on so that Mountains and the like can be shown in the distance, and then loaded in as the high poly terrain as you get close.
You could as b32 said, just loop these terrains so that when you leave the centere one going north (say), you draw the southern one as further north than the northen one. (But this makes the world a torus). It really depends on what you need.
So... imagine you want "Infinte Terrain" al la IGI, you have the real terrain as (say) the middle of a group. As the player leaves the middle terrain you are already showing the comp generated/standard terrain, but you the generate the one that the player is walking towards as well (Well the three they are walking towards, but lets not complicate it). Then as they reach the edge of the next terrain you .... etc.
Obviously you can do it differantly/better by (say) having a low res terrain "Under" the ones you are on so that Mountains and the like can be shown in the distance, and then loaded in as the high poly terrain as you get close.
You could as b32 said, just loop these terrains so that when you leave the centere one going north (say), you draw the southern one as further north than the northen one. (But this makes the world a torus). It really depends on what you need.