  We present a novel tightly-coupled LiDAR-inertial odometry and mapping scheme
for both solid-state and mechanical LiDARs. As frontend, a feature-based
lightweight LiDAR odometry provides fast motion estimates for adaptive keyframe
selection. As backend, a hierarchical keyframe-based sliding window
optimization is performed through marginalization for directly fusing IMU and
LiDAR measurements. For the Livox Horizon, a newly released solid-state LiDAR,
a novel feature extraction method is proposed to handle its irregular scan
pattern during preprocessing. LiLi-OM (Livox LiDAR-inertial odometry and
mapping) is real-time capable and achieves superior accuracy over
state-of-the-art systems for both LiDAR types on public data sets of mechanical
LiDARs and in experiments using the Livox Horizon. Source code and recorded
experimental data sets are available at https://github.com/KIT-ISAS/lili-om.
