Multipath-Closure Calibration of Stereo Camera and 3D LiDAR Combined with Multiple Constraints

Stereo cameras can capture the rich image textures of a scene, while LiDAR can obtain accurate 3D coordinates of point clouds of a scene. They complement each other and can achieve comprehensive and accurate environment perception through data fusion. The primary step in data fusion is to establish the relative positional relationship between the stereo cameras and the 3D LiDAR, known as extrinsic calibration. Existing methods establish the camera-LiDAR relationship by constraints of the correspondence between different planes in the images and point clouds. However, these methods depend on the planes and ignore the multipath-closure constraint among the camera-LiDAR-camera sensors, resulting in poor robustness and accuracy of the extrinsic calibration. This paper proposes a trihedron as the calibration object to effectively establish various coplanar and collinear constraints between stereo cameras and 3D LiDAR. With the various constraints, the multipath-closure constraint between the three sensors is further formulated for the extrinsic calibration. Firstly, the coplanar and collinear constraints between the camera-LiDAR-camera are built using the trihedron calibration object. Then, robust and accurate coplanar constraint information is extracted through iterative maximum a posteriori (MAP) estimation. Finally, a multipath-closure extrinsic calibration method for multi-sensor systems is developed with structurally mutual validation between the cameras and the LiDAR. Extensive experiments are conducted on simulation data with different noise levels and a large amount of real data to validate the accuracy and robustness of the proposed calibration algorithm.