Binocular stereovision system is regularly only calibrated once, that is each camera is calibrated using a picture of the calibration pattern laid in the cross field. This methods calibration accuracy is expected to be improved. A twice calibrating method is proposed here. Each cameras extrinsic and intrinsic parameters are calibrated in different fields. The extrinsic parameters are firstly calibrated in the cross field, then the intrinsic parameters are calibrated in the close-range field. By applying the method to one binocular stereovision system built in our lab, it is demonstrated that the proposed method can improve the calibration accuracy more than 3.4dB than the once calibrating method. Its accuracy makes this novel method more suitable for high accurate target tracking application.
