An auto-landing strategy based on pan-tilt based visual servoing for unmanned aerial vehicle in GNSS-denied environments

This paper proposes an unmanned aerial vehicle (UAV) rapid autonomous landing strategy in GNSS-denied environments using pan-tilt based visual servoing (PTBVS) system. First, we propose a PTBVS system for navigating the UAV landing on a square platform. Through the status of the airborne camera and image information, the relative position information between the UAV and landing point can be obtained for navigation. Second, we made the UAV move horizontally and vertically at the same time when returning, which greatly shortens the flight distance and reduces the landing time. Moreover, in different landing stages, we adopt different positioning information acquisition methods. When the UAV is approaching the landing point, it uses the PTBVS system for navigation. Instead, it uses the pixel coordinate offset of the landing point to further improve the landing accuracy when landing vertically. Finally, we put forward the PTZ and UAV control algorithm. The PTZ control which keeps the landing point in the center range of the image consists of the time delay and PID control. And the UAV control guides the UAV to return and land. We test the proposed landing algorithm in the simulation platform and the actual environment. It is proved that the proposed method can bring the UAV earlier visual foresight, less landing time, and higher landing accuracy.