A scheme for parameter calibration in super-size two-dimensional scale events sensing and positioning system using binocular stereo vision

摘要

Camera and system parameters calibration is an essential process for a distance measuring system using binocular stereo vision. In usual ways of calibration, brightly colored objects are put at the center of the area of surveillance to avoid big errors in measurement as targets are far away from the center. When calibration objects are not allowed to be put in the sensing area of interest, they should be placed somewhere else outside. A scheme of calibration is proposed for system parameters correction in super-size two dimensional scale events sensing and positioning system using binocular stereo vision. The location of a reference point is specified at the center of the surveillance area of about 200,000 meters square, and the coordinate of the center is known in the physical world. Coordinates of cameras and calibration objects outside the surveillance area are measured in physical world coordinates system. It is convenient to compute the angle between the side connecting camera with the calibration object and the one connecting the same camera with the reference point using the longitude and altitude values measured. When calibration is performed, orientation of the camera is obtained and position of the object on the imaging plane is read out in pixels. Rotating the camera with the angle computed above, the reference point would be on the optical axis of the camera in the ideal case. The accuracy of the device for measuring the angle contributes to the error in aligning the optical axis passing through the reference point. In the experiment, when putting a calibration object at the reference point, the position of the object on an imaging plane could be read out in pixels. Comparing the difference of pixels between the two orientations of the camera, errors caused by rotating the camera can be determined. When another camera is configured to form a binocular stereo vision system, parameters are calibrated in the same way. Theoretical analysis shows that the error caused by adjusting two cameras is limited by a shape that approximates a quadrilateral. The area of the quadrilateral is determined by both the accuracy of the angle measuring device and the distances between the cameras and the reference point. Comparison of theoretical with experimental results is made, indicating the effectiveness of this scheme.