Working with DEMs in Terragen
There are many programs that will convert DEMs into a format suitable for Terragen. This page describes how I use 3DEM to create my terrains from DEMs including joining multiple files together.
3DEM provides a Terragen export under the file menu but the size of the terrain is usually smaller than what you can squeeze out of the data. Instead, I save a BW version of the map image and import it into Terragen via the Firmament BMP import. To create the BW map in 3DEM requires a few small modifications.
The first modification is to get rid of any shading. This is easily done in the lighting parameters (Color Scale > Shaded Relief).
This places the sun directly above the terrain resulting in no shadows.
The next modification is to change the Terrain Colours (Color Scale > Modify Scale).
There is a world wide conspiracy of map makers that results in many places of interest being mapped to the corners of maps, requiring you to buy 4 maps. The same seems to apply for DEMs.
Unfortunately 3DEM only displays single DEMs. It is possible with a bit of work to join multiple DEMs in another image editing program. This is relatively straightforward if all of the images have the same altitude to pixels value settings. Firstly, load each section into 3DEM and take a note of the altitude range displayed in the Terrain Colors dialogue box. Take a note of the minimum and maximum altitudes of all of the images you want to join, round them to the nearest 100 metres (round down for minimum, round up for maximum) and use these to modify the Terrain Colours of each DEM and save each map image.
It's then a relatively straightforward to join process of joining the sections together, editing any minor glitches that may occur (e.g. small gaps). In this way it's possible.
e.g. Yosemite (1500x1850, 740kb zipped)
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