But if I zoom up to the same heightmap feature so that it is the same size on the screen, such as walking on the terrain in a video game, then the erosion is going to be the identical size between the two heightmaps. But again, if I Zoom Extents on a 1024 heightmap and a 4096 heightmap, the brushes on the 4096 heightmap will look one quarter the size, this is because I am zoomed out four times further. If I choose a 6 pixel brush, then it will be 6 pixels regardless of the size of the heightmap. It uses a вЂњbrushвЂќ of a specific size to simulate a raindrop of flowing water. But if I zoom up to the same heightmap feature so that it is the same size on the screen, such as walking on the terrain in a video game, then the erosion is going to be the identical size between the two heightmaps.ДЄs another quick example, letвЂ™s look at the Rain Erosion algorithm in TerreSculptor. The erosion cell is always a constant size, but if I look at a 1024 heightmap versus a 4096 heightmap, both at Zoom Extents, well of course the erosion on the 4096 heightmap will visually appear to be one quarter the size, this is because I am zoomed out four times further. Most erosion simulation algorithms use cellular automata, where the algorithm loops over the surface of the heightmap examining 3Г—3 cells for altitude difference and moving water and soil down to lower elevations. This same false view also seems to get applied to the modifiers, especially the erosion modifiers. If the width:height ratio was always a constant, then when I had a 20 km by 20 km terrain, would I expect the mountains to all be 20 km high? Even Mount Everest is only 8 km in elevation, not 20 km. The mountains donвЂ™t somehow grow in height when the area of land mass that I am using increases. If I Zoom Extents with differing heightmap resolutions, then the aspect will correctly change between them based on their resolution ratios. So the aspect ratio of width:height changes when I have a piece of heightmap that is getting larger in size, especially if I am Zoom Extents on all four terrains. Likewise if I go even larger, a 4 km by 4 km piece of that same digital elevation model, then I will be getting more mountains in my piece since the area is larger, but the mountains donвЂ™t become 4 times as high, the mountains with still be 1 km high (ratio 4:1). If I take a digital elevation model that is 1 km by 1 km that contains mountains that are 1 km high (width:height ratio 1:1), then I take a larger piece of that same digital elevation model, say a 2 km by 2 km piece, well the mountains will still be 1 km high (ratio 2:1), the mountains will not somehow double in height just because I have taken a larger area piece of that same digital elevation model.

I am looking at four times as much width area with the 4096 heightmap, so of course the height will be one quarter as much. If I look at a 1024 heightmap versus a 4096 heightmap, both of them with the same height mountains on them, both of them at Zoom Extents in the editor, well of course the 4096 heightmap will visually appear to be one quarter the altitude height range, this is because I am zoomed out four times further.

Many people seem to fall into this same false view of how 3D terrain worlds work. What you are creating is a larger area of a constant altitude range. That is simply an optical illusion of ratios. A larger heightmap size directly equates to a larger area of land, not a higher detail version of the same terrain mesh. It is a common misconception that changing the width and length resolution of the heightmap to a larger value somehow makes it shorter in altitude. Where most people seem to fall down on terrain software, is a larger heightmap value directly equates to a larger area of land, and not to a higher detail version of the same terrain mesh. It seems that I am constantly asked this same question every week, so I thought I would make an explanatory blog post about it.

Unreal engine 4 heightmap