DEM is used in Farming Simulator maps to define the terrain height.
Every hill, valley, and slope is defined by a DEM. While it may sounds complex, it's really just a 2D grid where each cell has a height value.
Image size: FS25 -> (map height + 1, map width + 1) FS22 -> (map height / 2 + 1, map width / 2 + 1)
Channels: 1
Data Type: uint16 (unsigned 16-bit integer)
File Format: .png
File Path: FS25 -> map_directory/data/dem.png FS22 -> map_directory/data/map_dem.png
DEM image is a single channel unsigned 16-bit integer image, which means that each pixel can have an integer value between 0 and 2^16 (65535). So, if the image can have values from 0 to 65535, while the highest point on Earth is 8848 meters, how does it work?
And this, where the heightScale parameter comes in. It's a value that converts the pixel value to it's in-game height. By default, in Giants maps, it's value set to 255, which means that the maximum possible value in the DEM image (65535) corresponds to a real world height of 255 meters. The selection of the actual value is up to you, you can play around with it to get the best result.
To set this value, you need to open the map.i3d file in Giants Editor, select the terrain on the Scenegraph tab, choose Terrain tab in the Attributes window, and set the heightScale parameter. After it you usually need to save the file and reload the map (File -> Reload).
In Farming Simulator 25 the size of the DEM image is usually the same as the map size but with an additional pixel in each dimension. For example, if the map size is 2048x2048, the DEM image size will be 2049x2049. But in Farming Simulator 22 the DEM image size is half of the map size. So, if the map size is 2048x2048, the DEM image size will be 1025x1025.
But actually, it can be changed using the unitsPerPixel parameter in the map.i3d file. It defines how many in-game units (meters) each pixel of the DEM image represents. So, in the FS25 by default, it's set to 1, which means that each pixel of the DEM image represents 1 meter in the game. But in FS22 it's set to 2, and that's why the DEM image size is half of the map size.
To set this value, you need to open the map.i3d file in Giants Editor, select the terrain on the Scenegraph tab, choose Terrain tab in the Attributes window, and set the unitsPerPixel parameter. Just a reminder, it should be an integer value. After it you usually need to save the file and reload the map (File -> Reload).