“…There are several applications of detected horizon including smooth navigation of unmanned aerial vehicles (UAVs) [17], [14], [23] and micro air vehicles (MAVs) [12], [13], [15], augmented reality [20], visual geo-localization and annotation of mountain/desert imagery [22], port security [16], and outdoor vehicle localization. Previous horizon line detection methods can be grouped into two major categories; (i) methods modeling sky and nonsky regions using machine learning [17], [12], [13], [16], [14], [15], [21] and (ii) methods relying on edge detection [19], [5]. Some attempts [1], [2], [20] have been made to combine these two approaches by eliminating non-horizon edges using classification; however, these attempts also fall under the second category as horizon detection is effectively based on edges.…”