This Autonomous Quadrotor Swarm Doesn't Need GPS

Without GPS or any other kind of external localization, a dozen of UPenn's quadrotors can fly in formation outdoorsImage: UPenn/YouTubeUPenn's autonomous quadrotor swarm doesn't need GPS or external localization to fly indoors or outdoors.
The vast majority of the fancy autonomous flying we've seen from quadrotors has relied on some kind of external localization for position information. Usually it's a motion capture system, sometimes it's GPS, but either way, there's a little bit of cheating in