In terms of terrain limitations, the actual mesh presents just as much of a limit as the testures. Each tile is made up of a fixed mesh. The tiles are visible from a certain range, measured from the tile centre. So, to make a highly detailed terrain tile, you are stuck with rendering a BIG mesh. Several tiles need to be visible, depending on the amount of 'fog' you have. Normal SDOE terrains had around 13,000 polys for the whole terrain mesh...which really doesn't go very far!

With a plane mesh, you would have low detail models... but the terrain mesh in SDOE does not allow this. If you make a low detail model, it will never join with the edges of the tile rendered in full detail. This is visibly horribly, and clearly visible. The 'background' colour is bright sky blue....

In practice...there is no real barrier to how big you make a terrain, other than the physical issue with hosting huge files.

You can't make the terrains overly detailed, in terms of mesh, since it brings a noticable slowdown even on reasonably fast terrains.

Finally...remember...no speedup or waypoint skipping. Do you REALLY want a terrain that takes hours to fly over?

Anyway...the way SDOE does terrains is unique. There is a reason for this...it's not a good way to do it! Games like UT2004 create terrains on the fly, and do so in varying degrees of detail as you move away from the viewer. Seamlessly. That's how it needs to be done.

I spent countless hours trying to make more physically detailed terrains for this sim, and gave it up as a waste of time.