The title says it all, but i will show you this video just to completelly understand what i want to do with 3D GameStudio
here

I'm working on a space simulation, and i've learned quite a bit about programming in Lite-C in the process. I actually got the idea from the game shown in the video, it has amazing graphics and scenery
But THAT one thing that i just can't understand is how game developers do this: While in space, the planet looks like a simple 3D Sphere, but the closer you get, the more detail it has. Then, at a point, it goes from a round model to a "flat" terrain surface. And then you can go back in space and watch it lose detail, and start to appear round again, etc...
I hope you understand my question

Thank you very much, im really enjoying my experience with GameStudio