That's quite something. I normally try to keep tabs on all the world sim projects, but somehow this one managed to completely slip under my radar. Good find.
Edit:
Trying it out a little. I wouldn't have expected billboarded trees to hold up this well at close range, but it does seem to work here. And I am particularly loving this grass. I see there is some LOD going on, but otherwise I can't tell how it works. HDR needs some work, though. Way too much glare.
A problem I've seen with most Rayleigh scattering implementations is that it doesn't look all that good from space. I'm not sure why, but it always seems to end up flooded with light.
- Spoiler:
This is a photo taken from low orbit. You can see scattering, but everything is still visible.
- Spoiler:
Here's a photo from in-game. It is difficult to see features clearly. I'm not sure how to fix this, or really even what the problem is. Even if you accommodate for a thinner atmosphere the higher up you go, that is still miles of full density atmosphere down to sea level, same as if you were looking across miles of land on the horizon. It seems like if everything on land disappears after a distance, the same should happen looking down, but in reality visibility never gets that bad. I've never heard an explanation for why this is.