Hello folks! I'm an arts instructor and painter and I intend to develop a series of works (not homework) based on the a troublesome issue (at least for me) that was out of our major in college and apparently no one I talked to had a solid answer for that. Considering that the horizon line is but a small piece of the Earth outline, and if you start to go up, the horizon line reveals itself as an arc and it is usual to think that the vanishing point lines gets curvy as well. But, is that correct? Imagine - if you think that most of the 3D representations considers the surface of the Earth a perfect flat shape - the observer and a series of objects (that go distorted by 3 VPs) suddenly starts to raise to a higher altitude and all objects keep the same distance to the observer. Do these lines keep straight to the horizon? Or you always have to consider the normal vector to the 'real' spheric surface of the Earth? And what about when you are in a distance that you can see the full shape of the Earth, how do the vanishing points work? I bet it gets worse when you consider our eyes circular perspective. Final... Perhaps I'm abstracting too much, but could that have something to do with a 'relationship' gravity-perspective ? Sorry If I couldn't use the correct math terminology. Any help or thoughts will be lots of useful. If there are studies regarding this I'd be pleased to know, since I couldn't find anything even googling. Thanks a lot!