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SHIELD: Spherical-Projection Hybrid-Frontier Integration for Efficient LiDAR-based Drone Exploration

Liangtao Feng, Zhenchang Liu, Feng Zhang, Xuefeng Ren

TL;DR

SHIELD addresses LiDAR-based drone exploration in large unknown 3D spaces with a quality-aware observation map and a hybrid frontier strategy, balancing exploration efficiency with reliable sensing. It augments traditional raycasting with an outward spherical-projection raycast and a one-time self-calibration to identify free space where returns are sparse. Global planning leverages an Hgrid-based ATSP framework and a CP subproblem to determine efficient visitation orders and viewpoints, while local planning uses B-spline trajectories in free voxels to ensure safe flight. Simulations and real-world experiments demonstrate improved path efficiency, robustness in open and constrained environments, and a public open-source release that facilitates further research.

Abstract

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.

SHIELD: Spherical-Projection Hybrid-Frontier Integration for Efficient LiDAR-based Drone Exploration

TL;DR

SHIELD addresses LiDAR-based drone exploration in large unknown 3D spaces with a quality-aware observation map and a hybrid frontier strategy, balancing exploration efficiency with reliable sensing. It augments traditional raycasting with an outward spherical-projection raycast and a one-time self-calibration to identify free space where returns are sparse. Global planning leverages an Hgrid-based ATSP framework and a CP subproblem to determine efficient visitation orders and viewpoints, while local planning uses B-spline trajectories in free voxels to ensure safe flight. Simulations and real-world experiments demonstrate improved path efficiency, robustness in open and constrained environments, and a public open-source release that facilitates further research.

Abstract

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.
Paper Structure (20 sections, 9 equations, 11 figures, 2 tables, 2 algorithms)

This paper contains 20 sections, 9 equations, 11 figures, 2 tables, 2 algorithms.

Table of Contents

  1. INTRODUCTION
  2. Problem Definition and System Overview
  3. Quality-Based Oberservation Map and Raycast
  4. Quality-Based Oberservation Map Construction
  5. Raycast based on Quality
  6. Hybrid-Frontier Strategy
  7. Frontier Detection and Clustering
  8. Viewpoint Generation
  9. Outward Spherical-Projection Raycast
  10. Outward Spherical-Projection Raycast
  11. Self‑Calibration of Spherical Projection
  12. Path Planning
  13. Hgrid State
  14. Hgrid Path Planning
  15. Coverage Path Planning
  16. ...and 5 more sections

Figures (11)

  • Figure 1: Outdoor open area exploration of SHIELD (a) UAV (b) First-person view (c) Point cloud map and trajectory (d) Hgrid and frontier distribution (e) Voxel map and spherical projection
  • Figure 2: Structure of SHIELD
  • Figure 3: Wrong raycast under big FOV
  • Figure 4: Observation of point cloud quality
  • Figure 5: Definition of the Hybrid Frontier
  • ...and 6 more figures