Depends on how you want to do it. The big boys use sensor blending and kinematic gps to get cm level accuracy. However that requires good GPS coverage (ie no

Depends on how you want to do it. The big boys use sensor blending and kinematic gps to get cm level accuracy. However that requires good GPS coverage (ie no roof) Second to that its fiducial tracking. Either attacking markers to each drone and using multiple cameras to work out 6 degrees of freedom, or giving the drones enough horsepower to do it onboard.