Wall inspection control of a VTOL unmanned aerial vehicle based on a stereo optical flow

An autonomous wall inspection control based on a stereo optical flow, suitable for unmanned aerial vehicles endowed with a stereo vision system, is proposed in this paper. The inspection task consists of simultaneously controlling the inspection velocity along the surface, the relative yaw angle between the vehicle and the observed plane, as well as the orthogonal distance. A virtual spherical camera is considered at the center of gravity of the vehicle. Then, a stereo optical flow, as if it had been acquired by the virtual camera, is generated from the visual data provided by the stereo vision system. The 3D visual measurements are also employed to estimate the relative position and orientation of the observed plane. Hence, the absolute vehicle velocity is estimated by using a robust translational average optical flow by integrating the total stereo flow. Finally, an inspection control and a hovering control are proposed. The effectiveness of the described approach has been demonstrated with a dynamic simulation in an environment composed of two adjacent walls.