On the note of heightfield data in the required format, I'm currently working on a photoshop tutorial that attempts to "fake" heightfield data at more or less 1km per pixel. I won't know how well it will perform until Outerra gives us that ability, but it should get you in the ballpark.
The image in
this thread shows a sample. The original is a 4096x4096 16-bit greyscale image. The island continent shown is approximately 1/4 to 1/2 the size of Australia. Basically, I took an original color map I created using
this technique as a baseline, then overlayed various greyscale colors to get "basic" heightfield data, and then use various cloud filters amongst others to try to make it a little more variable. I also use a greyscale version of the original map to give a few extra features, namely for mountain regions. The custom heightfield data more or less works in Lightwave, although refining it down to the cm level like Outerra doesn't work quite as well. Not to mention the render times are horrendous.
This is only one sample of an image I created in Lightwave using the heightfield data:
I think this one is about 1+km above the ground plane
This one is at typical human eye-level, looking off to the horizon (no fog effects enabled, so it's hard to sense the scale)
The mountains in this image are about 5km away, I think (I'll have to go back and check my maps to be sure)
Regardless, even with the bad renders here, it's close, so hopefully Outerra's refinement will make these images really shine
Too bad that ability is still in the distant future
*Edit* Public Facebook links not working ... will fix in a minute
*Edit2* Fixed distance