  Sensor calibration is the fundamental block for a multi-sensor fusion system.
This paper presents an accurate and repeatable LiDAR-IMU calibration method
(termed LI-Calib), to calibrate the 6-DOF extrinsic transformation between the
3D LiDAR and the Inertial Measurement Unit (IMU). % Regarding the high data
capture rate for LiDAR and IMU sensors, LI-Calib adopts a continuous-time
trajectory formulation based on B-Spline, which is more suitable for fusing
high-rate or asynchronous measurements than discrete-time based approaches. %
Additionally, LI-Calib decomposes the space into cells and identifies the
planar segments for data association, which renders the calibration problem
well-constrained in usual scenarios without any artificial targets. We validate
the proposed calibration approach on both simulated and real-world experiments.
The results demonstrate the high accuracy and good repeatability of the
proposed method in common human-made scenarios. To benefit the research
community, we open-source our code at
\url{https://github.com/APRIL-ZJU/lidar_IMU_calib}
