A code-level tour of IGNIS-8's LiDAR-inertial odometry: a FAST-LIO-style error-state Kalman filter fusing the L1 PM's 250 Hz IMU with its 20 Hz point cloud into a 6-DOF pose, plus a keyframe-based loop closer that detects revisits, confirms them by scan match and rebuilds the three-level voxel map without drift.