Quadrotor circumnavigation of an unknown moving target using camera vision‐based measurements

This study proposes a vision‐based motion estimation and target tracking algorithm for a quadrotor unmanned aerial vehicle circumnavigation around a moving mobile target whose velocity is unknown and time varying. In this study, the authors assume that the quadrotor is equipped with onboard downward‐looking camera, as a means to determine position of the quadrotor relative to the target. The proposed circumnavigation control algorithm relies essentially on two distinct phases, namely the virtual target tracking and the circumnavigation phase. To prepare for these phases, a predefined sphere, with a desired radius having the moving target position as its centre, is constructed along with a virtual target point that can move on its surface. During the whole tracking procedure, the quadrotor is first commanded to reach the virtual target point located at the projection of the ground vehicle's position onto the surface area of the sphere. When the quadrotor's position and velocity approaches the virtual target point with a given accuracy, the second phase is initiated to provide the quadrotor with more precise guidance to start orbiting at a specific height from level ground around the moving target. In this manner, the virtual target point is given the ability to manoeuvre itself in a circular motion above the moving target. The developed orbit manoeuvre uses an estimate of the moving target's velocity, obtained from a predictor scheme able to achieve velocity estimation as fast as possible.