Hi Rastar, Ill try that with the RAW format. The data we use is a mix of CAD contours, SRTM, photogrammetry, so generally accuracy varies quite a bit, starting at around 100 to 500 mm for the contours. We take it into Global mapper and merge it together.
We also use Unigine which can deal with very large terrains. Im in the process of seeing how big we can make terrains in UE4 using Landscape tiles. Ideally i would like to get 25 x 25 km terrains working. I havent looked into the data streaming yet, but have looked into problems that arise from not having double precision. At about 15km for the origin the editor camera jitters around a little bit, but its not too bad. We may need to move toward a camera centric world approach or a tile based sector approach to keep the camera near the origin.