I don't have the link to hand, but I've seen some very impressive demonstrations of quadrotor control in an enclosed space using 9DF sensing on each vehicle for basic flight control, and external fixed cameras picking up beacons on each unit to determine absolute positions to give precise control over the flight path. This seemed to give positioning down to accuracy of a couple of cm and enabled the drones to carry out complex manoeuvers very close to each other and to other objects. It looked as if it was the product of a substantial amount of effort over several years by a team of very smart people, and I think this would be very difficult to get working from scratch.
I haven't seen anyone doing it yet, but it seems to me that the IR position sensing technology being developed for CastAR would work very well as an onboard position sensor, so that the drone could work out its position and orientation relative to fixed beacons in the environment. Since the complex part of the beacon detection and geometry analysis is being done in hardware, there would be almost no overhead for this.