Matt, here is the requested example. Ignore the gray areas as the render was done in 3 parts for a 3 part canvas panel print. The gray bits are just my Photoshop backgroung colour. Just the effected area of the image is shown cropped down in PS. I have drawn a blue line starting at the left hand end of the horizon so that you can see the deviation. I suspect that the is not a lot I can do about this in Terragen 2 as the whole system is based on planets.
I have just done an edit in Photoshop and used the lens correction filter to straighten out the curviture deviation and it works quite well, but it does have to mess with the pixels so it is not ideal. My next problem is getting my camera centred correctly to the axis of the planet as, as you can see in the image not only am I getting a curved horizon but the two extreme ends of the horizon are also not lined up. Hope I am making sense!
Anyway, I have now gone from having Flat Earth Syndrome to being Lost in Space! lol
3DGuy, I have tried the narrowing the FOV out already but I get too zoomed and loose the effect I am after. I did this once on a render in 0.9 and the zooming created a big loss of detail and added pixelation. Might be worth trying out in 2 to see if procedural surfaces give the same effect.