Online calibration of infrared binocular vision measurement system with large field of view

High-precision calibration of a binocular vision measurement system is the foundation of the precise measurement in a large field of view (FOV). Given the complexity of light variation in a variety of workplaces, an optical reference target, which has five strong reflective feature points, is designed in this paper. Aiming at the self-designed target, this paper puts forward an online calibration method of the binocular vision measurement system. Because of the strong reflective properties, the feature points produce a sharper image in infrared light. In the different locations of the intersection area of the binocular vision being measured, the target has been placed five times. According to the image co-ordinates of feature points and distance constraints between feature points, the intrinsic parameters of cameras and structure parameters of the binocular vision measurement system are simultaneously estimated by the proposed method. This method is simple and applicable for all kinds of workplaces. Even without pre-calibration, the vision measurement system produces fairly high accuracy using this method. With the maximum error of 0.079 mm in the measurement range of 4500 mm (length)×4300 mm (wide)×3000 mm (distance), the experimental results have proved the effectiveness of the proposed calibration method for online calibration.