Ahahahahaa
Alberto :
read lot more posts, or use 3DGS some more or the demo if you don't own the engine.

Unity has lot fo features and tools that 3DGS don't have for terrain.
in some clicks you can have a relective water, you can paint folliage, trees on terrain and also standard tools to edit/paint terrain.

And Unity is more powerfull can handle terrain with all trees folliage and Next Gen scenes with soft shadows,shaders(normal/specular),lights all integrated,
ready to use.

Go to Unity site and look at editor interfaces/features

ahahahahaaaa
Alberto where have you been the last 6 months ?