A. Passive System
The pocket size drones (Figure 2b) were used indoors to
test the passive method. In first experiments, a target drone
was flown manually inside an empty room, with dimensions
(6 × 3.5 × 3) meters, where a perceiving drone was resting on
the ground in the center of the room with engines off. A motion
tracking system was used for measuring the true robot positions
and to compute the actual 3D relative bearings between