Hi. Most modern camera quadcopters (drones) have a "follow" function, allowing them to follow and film a person. The DJI Phantom 4 does this by optical tracking, most other brands require that the person carry a smartphone or other wearable. How does this work? I assume the smartphone or wearable sends a signal, but how can a single drone determine its distance and direction from the source? Obviously not by triangulation. Or is it that simple that both the smartphone/wearable and the drone must have GPS and the drone simply receives the coordinates of the sender, compares them with its own and follows? But is this fast and accurate enough? As far as I know GPS is only accurate to a couple of meters, which could bring the drone dangerously close to the person it follows so far away that the camera shots become useless.