Operation Flashpoint, VBS1: Set desired terrain resolution (in meters).
For default landscapes, supported resolutions are:
50 - Smoothest, less lag
25 - Default in Multiplayer
12.5 - Default in Singleplayer
6.25
3.125 - Bumpiest, higher lag
If you select unsupported resolution, nearest supported value is used instead.
Armed Assault, VBS2: Terrain resolution is fixed, determined by the world created.
This function controls terrain LOD instead (the distance in which the terrain mesh resolution starts to degrade).
Higher number means less vertices are used for terrain rendering, making distant hills less smooth.
Value 12.5 corresponds to selecting Terrain Detail Normal in Video options, 50 to Very Low, 3.125 to Very High.
This is like opening up your video preferences and changing "terrain detail", i.e.
setTerrainGrid 25 = lowest detail
setTerrainGrid 3.125 = highest detail
It is similar to the command setViewDistance.