  Cooperative Unmanned Aerial Systems (UASs) in GPS-denied environments demand
an accurate pose-localization system to ensure efficient operation. In this
paper we present a novel visual relative localization system capable of
monitoring a 360$^o$ Field-of-View (FoV) in the immediate surroundings of the
UAS using a spherical camera. Collaborating UASs carry a set of fiducial
markers which are detected by the camera-system. The spherical image is
partitioned and rectified into a set of square images. An algorithm is proposed
to select the number of images that balances the computational load while
maintaining a minimum tracking-accuracy level. The developed system tracks UASs
in the vicinity of the spherical camera and experimental studies using two UASs
are offered to validate the performance of the relative visual localization
against that of a motion capture system.
