A Stepwise Minimum Spanning Tree Matching Method for Registering Vehicle-Borne and Backpack LiDAR Point Clouds

Vehicle-borne laser scanning (VLS) and backpack laser scanning (BLS) are two emerging mobile mapping technologies for capturing detailed spatial information near ground in urban built environments. BLS has flexible mobility and usually provides point clouds in a local coordinate system. Therefore, a mismatch between VLS and BLS point cloud data is quite common. Fusing VLS and BLS data in different coordinate systems could provide a comprehensive survey of urban built environments. Because of the complexity of urban road environments and the difference in data acquisition methods, traditional registration approaches based on point-level correspondences are likely to fail and sometimes involve substantial manual efforts. In this article, we propose a novel registration approach that finds the optimal transformation between the respective point clouds based on a unique tree distribution pattern defined by tree trunk centers. The proposed method consists of three key steps, i.e., trunk center extraction, stepwise minimum spanning tree (MST) matching, and transformation estimation. Stepwise MST matching is an essential step in finding the one-To-one correspondences using a topological similarity between the two light detection and ranging (LiDAR) datasets. We evaluated our method with five real-world datasets collected in Shanghai, China. The results showed that the proposed method performed well in all five experiment sites with an average rotation error of less than 0.06_ and an average translation error of less than 0.05 m. Moreover, the reported mean position deviation in the five sites is 0.112, 0.144, 0.176, 0.148, and 0.184 m. Our proposed method has a great potential for registering multiplatform LiDAR data that could provide comprehensive and essential 3-D information for numerous urban applications.