Real-time 3D mapping of large-scale Global Navigation Satellite System (GNSS)-denied environments plays an important role in forest inventory management, disaster emergency response, and underground facility maintenance. Compact helmet laser scanning (HLS) systems keep the same direction as the user’s line of sight and have the advantage of “what you see is what you get”, providing a promising and efficient solution for 3D geospatial information acquisition. However, the violent motion of the helmet, the limited field of view of the laser scanner, and the repeated symmetrical geometric structures in GNSS-denied environments pose enormous challenges for the existing simultaneous localization and mapping (SLAM) algorithms. To promote the development of HLS and explore its application in large-scale GNSS-denied environments, the first large-scale HLS dataset covering multiple difficult GNSS-denied areas (e.g., forests, mountains, underground spaces) was built in this study. Besides using an additional very high accuracy fiber-optic inertial measurement unit (IMU), a novel post-processing multi-source fusion method—progressive trajectory correction (PTC)—is proposed to generate a reliable ground-truth trajectory for the benchmark, which overcomes the problems of scan matching degradation and non-rigid distortion. The accuracies of the ground truth are controlled and checked by manually surveyed feature points along the trajectory. Finally, the existing state-of-the-art SLAM methods were evaluated on the WHU-Helmet dataset, summarizing the future HLS SLAM research trends. The full dataset is available for download at: https: //github.com/kafeiyin00/WHU-HelmetDataset.

Rigorous boresight calibration between light detection and ranging (LiDAR) and the camera is crucial for geometry and optical information fusion in earth observation and robotic applications. Although boresight parameters can be obtained through pre-calibration with artificial targets, unforeseen movement of sensors during data collection can lead to significant errors in the boresight parameters. To address this issue, we propose SE-Calib, an automatic and target-free online boresight calibration method for LiDAR-Camera systems. SE-Calib firstly extracts semantic edge features from both point clouds and images simultaneously using the 3D semantic segmentation (3D-SS) and 2D semantic edge detection (2D-SED) methods. The boresight parameters are then optimized with an adaptive solver and maximizing the Soft Semantic Response Consistency Metric (SSRCM) scores iteratively. The SSRCM is designed to evaluate the coherence of cross-modular semantic edge features, and a confidence function is proposed to filter out unreliable optimization results. Experiments conducted on challenging urban datasets show an average boresight error of 0.206 degrees (2.47 pixels in reprojection error), demonstrating the effectiveness and robustness of the proposed method.