This paper introduces SHIELD, a Spherical-Projection Hybrid-Frontier Integration for Efficient LiDAR-based Drone exploration method. Although laser LiDAR offers the advantage of a wide field of view, its application in UAV exploration still faces several challenges. The observation quality of LiDAR point clouds is generally inferior to that of depth cameras. Traditional frontier methods based on known and unknown regions impose a heavy computational burden, especially when handling the wide field of view of LiDAR. In addition, regions without point cloud are also difficult to classify as free space through raycasting. To address these problems, the SHIELD is proposed. It maintains an observation-quality occupancy map and performs ray-casting on this map to address the issue of inconsistent point-cloud quality during exploration. A hybrid frontier method is used to tackle both the computational burden and the limitations of point-cloud quality exploration. In addition, an outward spherical-projection ray-casting strategy is proposed to jointly ensure flight safety and exploration efficiency in open areas. Simulations and flight experiments prove the effectiveness of SHIELD. This work will be open-sourced to contribute to the research community.

翻译：本文提出SHIELD，一种基于球面投影混合前沿集成的激光雷达无人机高效探索方法。尽管激光雷达具备宽视场的优势，但其在无人机探索中的应用仍面临若干挑战。激光雷达点云的观测质量通常低于深度相机。基于已知与未知区域划分的传统前沿方法计算负担沉重，尤其在处理激光雷达宽视场数据时更为明显。此外，缺乏点云的区域也难以通过光线投射归类为自由空间。为解决这些问题，本文提出SHIELD方法。该方法维护观测质量占据地图，并在此地图上执行光线投射，以解决探索过程中点云质量不一致的问题。采用混合前沿方法以应对计算负担与点云质量探索局限性的双重挑战。此外，提出一种外向球面投影光线投射策略，共同保障开放区域中的飞行安全与探索效率。仿真与飞行实验证明了SHIELD的有效性。本工作将开源以促进研究社区发展。