TWO: A Simple Method of Directly Closing the Loop for LiDAR Odometry

In this paper, we propose a simple method, termed TWO, of directly closing the loop for LiDAR odometry. TWO suggests assigning high weights to the LIDAR observations corresponding to the old parts of the map; since these parts are built with the low-drift poses from the early odometry and can help drag the drifted odometry back to the correct global position when the LiDAR scans the points of these parts again. Also, we present the method of checking the consistency of the plane normal to address the two-side problem that may cause damage when using TWO. Moreover, we show that the proposed method is lightweight and needs little extra computation and storage space compared to the original odometry. The proposed TWO is integrated into the state-of-the-art LiDAR odometry A-LOAM and LiDAR-inertial odometry FAST-LIO2, and it is tested thoroughly on five public datasets and our private handheld dataset. The experiments show that the TWO can effectively help these two methods directly close most loops and produce localization results with apparently lower drifts.