“…This task is of demand in navigating small unmanned aerial vehicles (UAVs) [1,2,3] and micro air vehicles (MAVs) [4,5,6], visual geolocalization [7,8], ship detection [9,10] and outdoor robot/vehicle localization [11,12,13]. The horizon line can be detected by (i) modeling sky and non-sky regions using machine learning [1,2,4,5,6,9,22] and (ii) employing edge detection [14,15].…”