The Tracer and the Orbiter

State Diagram

The state diagram shown above may seem daunting at the first glance, while in fact is is a relatively simple repetition of the simple coordination pattern shown in the multiple vehicle coordination page. At the highest level the simple coordination mechanism is applied four times: for coordinated take-off, for moving to the next waypoint, for returning to launch (rtl), and, finally, for landing. In each case, at the beginning of the action, the two vehicles first report to the ground coordinator that they are armed, and then enter the wait_loop state, waiting for the signal (a remotely triggered state transition) to start the action, then, upon completing the action informing the coordinator. The coordinator first waits for both drones to confirm that they are armed, then it reads the the .plan file and commands next_waypoint transitions for each waypoint in the .plan file (when the file is done, an rtl is commanded). The Orbiter has extra states, as, once at the next_waypoint, it needs to orbit, while the Tracer simply stays put (in the wait_loop) until the next command from the coordinator. The script exercises all three coordination mechanisms documented on the multiple vehicles coordination page. 

Note that the movements of the two vehicles at the next point are safe, as both vehicles are given the same vector of movement (leading to parallel trajectories): even if the two vehicles would move at different speeds, they would still avoid collisions. The difference in altitude (5m in the sample experiment) provides an additional layer of safety.