This is hypothetical and more curious. If I take off within side a train will the Phantom 4 move with the train or will it stay in that spot until it crashes into the back of a train. Would the VPS sensors know about the ground and lock on? Also has any one ever flown outside of a train while being in a train? I am curious as to what sort of signal and if it could keep up between stops (I imagine it would). Iv also thought about wave points to fly from one stop to the next. I would never try flying over a train because there is high electrical wiress and its going to be a mess if you crash. As I said this is more hypothetical. Please do not try this at home.