Comparing to POV-Ray, relative detail/number of samples, corresponds to "count", and GI sample quality should correspond to "error bound", which specifies how blurred the taken samples are. In POV-Ray a high number in error bound, specifies a low accuracy.
The images below, show:
First, default settings for radiosity (or GI), which is 35 samples at a blurring of 1.8 (low detail - low quality), which doesn't look bad for this kind of scene, but would look awful in a more detailed scene, where a color would "bleed out" where it shouldn't.
The second image keeps the same number of samples/detail, but reduces blurring (from 1.8 to 0.1)/increases accuracy/quality (numbers in this setting in POV-Ray are opposite from Terragen, better is lower, instead of higher). This doesn't look good, since individual samples can be seen.
The third image increases samples/detail from 35 to 350 (which for this image size is enough, a bigger image would need more), keeping the blurring low - accuracy/quality high. Although the differences from the first image are not great, looking closely, one can see that the third is more accurate than the first: the red tiles give a red color to the sphere and the shadow is darker near the bottom of the sphere.
There are other qualities in radiosity/GI, but I believe the main one is to keep your objects' textures at ambient 0 (black) and depend on GI to light up the shadows for a more natural look. I don't believe Terragen supports interreflections in GI, but I could be wrong.
Helen
