**Abdul Majeed and Sungchang Lee \***

School of Information and Electronics Engineering, Korea Aerospace University, Deogyang-gu, Goyang-si, Gyeonggi-do 412-791, Korea; abdulmajid09398@kau.kr

**\*** Correspondence: sclee@kau.ac.kr; Tel.: +82-10-3232-5237; Fax: +82-2-3159-9969

Received: 11 March 2019; Accepted: 4 April 2019; Published: 8 April 2019

**Abstract:** This paper presents a new coverage flight path planning algorithm that finds collision-free, minimum length and flyable paths for unmanned aerial vehicle (UAV) navigation in three-dimensional (3D) urban environments with fixed obstacles for coverage missions. The proposed algorithm significantly reduces computational time, number of turns, and path overlapping while finding a path that passes over all reachable points of an area or volume of interest by using sensor footprints' sweeps fitting and a sparse waypoint graph in the pathfinding process. We devise a novel footprints' sweep fitting method considering UAV sensor footprint as coverage unit in the free spaces to achieve maximal coverage with fewer and longer footprints' sweeps. After footprints' sweeps fitting, the proposed algorithm determines the visiting sequence of footprints' sweeps by formulating it as travelling salesman problem (TSP), and ant colony optimization (ACO) algorithm is employed to solve the TSP. Furthermore, we generate a sparse waypoint graph by connecting footprints' sweeps' endpoints to obtain a complete coverage flight path. The simulation results obtained from various scenarios fortify the effectiveness of the proposed algorithm and verify the aforementioned claims.

**Keywords:** coverage flight path planning; footprints sweep; waypoint graph; navigation; urban environments; unmanned aerial vehicles
