Vision-based Pan-tilt unit error measurement

As a ground-based visual guidance system for autonomous UAV landing. In this paper, the cameras mounted on PTUs are used to dynamically measure the movement parameters of the UAV during the approaching phase. Owning to the limitation of manufacturing precision, there will be kinematic errors of PTU. In order to ensure the accuracy of UAV´s attitude obtained, the exact error of PTU should be obtained and compensated. In this paper, we only adopt the camera of system to measure the error of PTU with no other sensors. Prior to the measurement, the camera should be calibrated. Then the calibrated camera mounted on PTU captures the chessboard of fixed position to obtain the extrinsic matrix of the PTU. By comparison between the real changes of PTU´s attitude and ideal changes, we could obtain the exact error of PTU. According to the distribution of the error, we adopt the spline curve modeling and compensate the errors. The results shows, the errors are reduced significantly.