SLIM: Scalable and Lightweight LiDAR Mapping in Urban Environments

Light detection and ranging (LiDAR) point cloud maps are extensively utilized on roads for robot navigation due to their high consistency. However, dense point clouds face challenges of high memory consumption and reduced maintainability for long-term operations. In this study, we introduce scalable and lightweight LiDAR mapping (SLIM), a scalable and lightweight mapping system for long-term LiDAR mapping in urban environments. The system begins by parameterizing structural point clouds into lines and planes. These lightweight and structural representations meet the requirements of map merging, pose graph optimization, and bundle adjustment, ensuring incremental management and local consistency. For long-term operations, a map-centric nonlinear factor recovery method is designed to sparsify poses while preserving mapping accuracy. We validate the SLIM system with multisession real-world LiDAR data from classical LiDAR mapping datasets, including KITTI, NCLT, HeLiPR, and M2DGR. The experiments demonstrate its capabilities in mapping accuracy, lightweightness, and scalability. Map reuse is also verified through map-based robot localization. Finally, with multisession LiDAR data, the SLIM system provides a globally consistent map with low memory consumption ($\sim$ 130 KB/km on KITTI).