Rendering a Terragen 2 scene in DIRSIG

Terragen is a terrain modeling software package that has both a free version and a commercial version available for download. This program has a nice procedural engine for synthesizing realistic terrain relief in a matter of a few minutes. Within Terragen 2 Deep Edition, we created a simple fractal based terrain with a spatial extent of 10km x 10km and exported it to OBJ format via the "micro exporter" contained with the Render node.

For the DIRSIG render, we simply created a mid-latitude summer (MODEL=2) and 23km aerosol model (IHAZE=1) MODTRAN based atmosphere and attributed the terrain with a 30% spectrally flat albedo. For a little sizzle, we also added a simple rectangular box and attributed with the fresnel optical property of water (n = 1.33, k=0.0).

Additionally, it should be noted that we had to manually rotate the OBJ file (within Blender and re-saved to the same file) by 90 degrees since Terragen uses the +Y is up convention while DIRSIG uses the +z is up convention. The resulting DIRSIG render has some similarities and slight differences compared to the terragen render.

DIRSIG render purposely did not use vertex normal interpolation in order to keep the OBJ file size small, resulting in a slightly more triangulated appearance
DIRSIG render has realistic downwelled and sensor path radiance and transmission losses that are not present (visually at least) in the Terragen render

Here is the DIRSIG scene zip file if you are interested in having a go yourself. terragen.zip

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LIDAR Point Cloud Visualization

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