HFT-LIC: Hierarchical Fast Targetless Lidar and Inertial Measurement Unit Online Calibration based on Global Navigation Satellite System

Autonomous navigation capability serves as the fundamental guarantee for unmanned platforms to accomplish various tasks. Variations in sensor extrinsic parameters can significantly impact their performance. To address this challenge, this paper proposes a hierarchical, fast, and targetless Lidar and inertial measurement unit(IMU) online calibration algorithm based on the Global Navigation Satellite System (GNSS) to achieve real-time calibration. First, the integrated navigation system are constructed using GNSS and IMU measurements. And Lidar odometry is built. Subsequently, the Lidar-IMU extrinsic parameter is coarsely estimated based on integrated navigation. Then, a graph optimization framework is employed to refine the Lidar- IMU extrinsic parameter. Next, the Lidar angular velocity is estimated under a constant-velocity model, and the time offset between the Lidar and IMU is calculated. Experiments are conducted in both structured and unstructured environments. The results show that, compared to open-source Lidar-IMU calibration algorithms, the proposed method exhibits superior environmental robustness, faster calibration speed, and a more user-friendly operational workflow.