An accurate two-step calibration method for circle-structured light system in pipeline inner surface profilometry

Circle-structured light systems offer an effective solution for the high-precision profilometry of pipeline inner surfaces. However, their measurement accuracy is significantly affected by errors in multi-camera extrinsic calibration and structured light plane parameters. To address this, the paper proposes a two-step calibration method. First, global camera calibration under limited overlapping fields of view is performed using a multiposition hollow cylindrical target. Second, based on the calibrated camera parameters, the structured light plane parameters are optimized by incorporating a ray-cylinder intersection constraint. This strategy reduces the complexity of parameter optimization and enhances calibration stability and accuracy through stepwise constraints. Experimental results demonstrate that the proposed method effectively improves the measurement consistency and accuracy of the system, providing a reliable and practical solution for pipeline inner surface profilometry.