Generally, things will start showing up when they are 1 pixel big. The engine computes on-screen size of things and if the objects cross the threshold they will appear. Although, at that distance aerial fog plays a significant role so they might not be even visible.
Excellent! At least they don't suddenly pop-up at 10nm like in FSX which is pathetic.
Aerial fog? Is this a technique you use to obscure objects/terrain off in the far distant so you don't have to render them? In that first shot it seems the fog is still letting the terrain (and presumably objects if bigger than 1px) show though even at about 40nm?
I should mention that in FSX terrain is visible at more than 150nm (though objects are not visible past 10nm). I think I saw in one of your videos the terrain being visible at very great distances as you zoomed out to space. XPlane limits terrain and object visibility to about 25nm before everything is fogged out, that is a joke for high level flight!
Also, for performance users with less capable machines might have to slide the quality multiplier down, say to .25 and this would cull a lot more objects, but some objects are more important to see than others!
For example, in a flight simulator I might like to have airports (runways and buildings) show at a quality of 1.00 but other less important objects (eg houses) show at a quality of .25.
Is it possible for your engine to accommodate this? I guess the engine needs to know what "class" of scenery the object belongs too and then apply quality factors based on the class... this gives users the ultimate tweak-ability to suit their hardware and personal FPS tolerance!
Please consider "tweak-ability" when designing your engine. You have no idea how much FSX/FS9 users tweak various settings in order to balance smooth FPS against nice visuals, especially when running complex aircraft which are simulating/rendering complex systems (eg PMDG 747, MD11 or LDS 767).
