These are the five heightmaps composing Helgoland and Dune, assembled together:
As a test, I selected all the white pixels (#ffffff). If there was an univocal correspondance between grey values on the raw maps and elevations in game, I would have expected pixels with the same intensity to coincide with areas having at least similar heights. Well, this is the result of my selection, overlayed to the chart of the two islands, as we see it on the navigation map:
Obviously some kind of noise gets applied to the height information of those heightmaps, and/or they don't represent absolute elevation values, but variations of elevation over terrain elevation data stored in TerrainData.BFD
