A binocular calibration method based on a coded 1D target for large-field measurement

Abstract

To address the practical difficulty of deploying large planar targets in large-field binocular calibration and the insufficient accuracy and robustness of existing calibration methods based on one-dimensional (1D) targets, a binocular calibration method based on a coded 1D target is proposed. First, an effective matched observation set is constructed through coded point centre extraction, cross-view matching, and epipolar distance screening, and is then divided into an accuracy evaluation observation set and a candidate calibration observation set. Then, during each single calibration process, a calibration subset is randomly sampled from the candidate calibration observation set, and the initial binocular parameters are obtained through fundamental matrix estimation and refinement, initialisation based on the physical parameters of the cameras, essential matrix decomposition, and rod length constraints. The optimisation variables are further released stage by stage during optimisation, enabling the optimisation of intrinsic, extrinsic, and distortion parameters while suppressing interference from parameter coupling. Finally, multiple single calibration results are evaluated in a unified manner on the fixed accuracy evaluation observation set, and the final calibration parameters are selected according to the minimum error criterion. Experimental results show that the mean reprojection error and mean absolute error of the proposed method are 0.0277 px and 0.0422 mm, respectively, both of which are lower than those of the comparative methods. The proposed method also maintains stable calibration performance under different object depths and different binocular baseline lengths. When a standard sphere device is reconstructed, the maximum error of the sphere centre distance is 0.117 mm. The proposed method avoids dependence on a large planar target while ensuring calibration accuracy and robustness, thereby providing a technical solution for the calibration of visual measurement and three-dimensional reconstruction systems.