I am struggling with designing black map and fog of war in a 3d game. Black map is the area that player hasn't explored (completely unknown), while fog of war is the area that player has explored and knows geospatial topology, but no friendly units or buildings are nearby to provide player with up-to-date info about enemy movements over the area.
The problem is that my terrain is 3D, varies in height greatly and camera can be placed at any position on the map at virtually any angle.
So far I've designed very heavy fog/clouds for area under fog of war, but not so heavy that the terrain underneath would not be visible, and am not rendering non-environment objects on those locations, but black map is another story.
Simply not rendering terrain over those locations looks and feels bad, and rendering terrain in pure black is not good as, when the camera is angled to view forward, player can still see elevation - very important information in the game and should not be given away without having to explore the map.
Are there any generally accepted ways of implementing such feature?