You have to make heightmap, in software like L3DT or World Machine. Good start here I know it's for LIDAR one, but similar to mentioned above: [Tutorial] Level Building with LIDAR. I think actually we don't have good tutorials. Might I should make complex one @Nadeox1 ?
I hadn't heard of world machine before I got it, and within 4 hours I had made the most incredible terrain I've ever made for a game. There are fantastic tutorials around, literally just type, "World Machine Tutorial" in youtube and have at it! There is a learning curve, and some knowledge of how and why things work required but it's really very straight forward and very logic-based.
World Machine is fantastic and really fun to experiment with. When modifying a terrain I use the editor in small areas and very incrementally. I have found when using the editor extensively it produces bad 'distance' jaggies that become really annoying and time consuming to fix, often changing the entire look of what I was after in the first place. The goal of good, jagged and realistic mountains for example is almost impossible to obtain with out those ridiculous jaggies or LOD style pop in. My recommendation to ANY map maker for BeamNG is to use an outside program like World Machine for heightmaps. The T3D editor while fun to play with needs a lot of work still yet.
