A cross-target-based accurate calibration method of binocular stereo systems with large-scale field-of-view

This paper presents an accurate calibration method of binocular 3D measurement systems for industrial on-site inspection, which uses a cross target with ring coded points. The cross target can be used to calibrate large-scale field-of-view stereo measurement systems and obtain higher measurement precision conveniently. The world coordinates of these ring coded points are not required. All we need is the distance of two ring coded points as a scale. A new calibration model with 10 distortion parameters for each camera is proposed. The calibration initial values are computed using the relative orientation method and the Direct Linear Transform (DLT) method of photogrammetry. The bundle adjustment algorithm is used to optimize the calibration parameters as well as the 3D coordinates of the ring coded points. Experiment results show that the RMS error of the reprojection in our method is less than 0.05 pixels and the measurement error is 0.011 mm compared with the Coordinate Measuring Machine (CMM).