A Point Cloud Slice-based UAV SLAM Method for 3D Reconstruction of Large Container Port Areas
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摘要: 在大型集装箱港区堆场环境中,大量重复性语义特征以及部分退化场景导致无人机在大面积场景下难以实现高效可靠的三维重建。为此,该文提出一种基于无人机点云切片同步定位与建图(SLAM)的大型集装箱港区三维重建方法,基于地面约束与点云密度梯度变化自适应提取多层切片点云,高效精准获取堆场语义信息,并基于同层切片点云匹配有效改善了里程计以及回环检测的精度。首先提出一种面向快速特征提取的点云切片方法,通过快速提取主方向并将点云划分为多层切片,高效获取多层语义点云。其次基于集装箱堆场场景特点进一步优化切片提取方法,基于重力方向简化场景主平面提取过程,并通过点云梯度变化自适应获取各层集装箱所在高程区间,构建多层切片点云。然后构建基于切片点云的递进式自适应激光里程计,利用高程切片自适应判别退化场景,同时在层间利用增量式迭代策略实现切片融合匹配,从而提升激光里程计精度、效率与稳定性。此外,设计融合激光点云切片信息的因子图优化方法,通过对多层切片点云匹配结果进行融合投票,筛除错误结果并减少大量重复结构对回环检测的影响,并利用切片因子来构建因子图边,从而提升全局优化水平,实现高效稳定的三维重建。最后,通过Carla仿真场景以及武汉某大型集装箱港区的实际场景测试,证实了该方法的可行性和有效性。Abstract:
Objective With the continuous development of port intelligence, the demand for digital management in container port areas has increased. In large container yards, Three-Dimensional (3D) reconstruction of the yard environment can be achieved using Unmanned Aerial Vehicle (UAV)-based Simultaneous Localization And Mapping (SLAM). However, container port areas contain many repetitive semantic structures. Traditional semantic matching methods therefore show low efficiency and limited accuracy. In addition, lanes between container yards form large feature-sparse regions during UAV-based 3D reconstruction, which can cause odometry degradation. Repetitive scene features also interfere with loop closure detection. To address these problems, this paper proposes a rapid feature extraction method based on point cloud slicing and further optimizes it according to the structural characteristics of container yards. A UAV point cloud slice-based SLAM method, termed Slice-SLAM, is proposed for high-precision 3D reconstruction of large container port areas. Methods To improve point cloud semantic extraction, a rapid point cloud slicing method is proposed. The principal direction is extracted rapidly, and the point cloud is divided into multiple layers to obtain multi-layer semantic point clouds efficiently. The slicing strategy is further optimized for container yard scenarios. Principal plane extraction is simplified using the gravity direction, and the elevation range of each container layer is obtained adaptively from point cloud density gradient changes. Multi-layer slice point clouds are then constructed. A progressive adaptive Light Detection And Ranging (LiDAR) odometry method based on slice point clouds is developed. Elevation slices are used to identify degenerate scenarios adaptively, and a layer-wise incremental slice matching and fusion strategy is used. This improves the accuracy, efficiency, and stability of LiDAR odometry. In addition, a factor graph optimization method that integrates slice point cloud information is designed. Fusion voting is performed on the matching results of multi-layer slice point clouds to remove erroneous matches and reduce the effect of repetitive structures on loop closure detection. Slice factors are then used to construct factor graph edges, which improves global optimization and supports efficient and stable 3D reconstruction. Results and Discussions The feasibility and effectiveness of the proposed method are verified in CARLA simulation scenarios and real-world tests at a large container port in Wuhan. First, comparisons with three semantic extraction algorithms, namely RANSAC, Region Growth, and 3DG_SEG, demonstrate the efficiency and accuracy of the proposed semantic extraction method. Second, estimated trajectories are compared with those obtained by two open-source LiDAR algorithms, FAST-LIO2 and Faster-LIO, confirming the advantages of the proposed odometry method. Finally, speed and confidence score are compared with those of six algorithms: ICP, NDT, GICP, Fast-GICP, Scan Context+ICP, and Quatro. The loop closure detection module of LIO-SAM is also integrated into FAST-LIO2, and the Scan Context module is integrated into Faster-LIO. The resulting estimated trajectories are compared with those of the proposed method, verifying the effectiveness of the proposed loop closure detection algorithm. The proposed method achieves high 3D reconstruction accuracy and is suitable for practical port operations. Conclusions The proposed method uses an efficient point cloud slicing technique and a multi-layer slice matching mechanism. Points within the same elevation range are defined as a slice point cloud, and the segmentation process is defined as point cloud slicing. This design enables efficient and robust 3D reconstruction in large-scale scenes with repetitive features. First, the LiDAR point cloud is aligned with the positive Z-axis using the gravity direction derived from the Inertial Measurement Unit (IMU). A sliding window records density gradient changes to determine the elevation range of each layer adaptively. This simplifies point cloud slicing and reduces the effects of non-standard containers and ground height variations on semantic extraction. Multi-layer slice information is then integrated into the odometry module to detect degenerate scenarios. Under normal conditions, progressive slice matching is used to initialize pose estimation. In degenerate scenarios, iterative Kalman filtering with increased IMU weighting is used. Finally, the fusion voting mechanism removes outliers from multi-layer slice matching results. The optimal match is used to initialize loop closure for global registration of container-region point clouds, enabling dual-stage loop closure detection and slice factor construction. By integrating slice point cloud information into factor graph optimization, the proposed method unifies point clouds in a common coordinate system and achieves efficient and robust 3D reconstruction. -
表 1 实验参数表
参数 $ {\lambda } $ $ \alpha $ $ \beta $ $ {\delta }_{t} $ $ {\delta }_{\theta } $ 飞行高度 $ \tau $ 数值 0.85 0.6 0.4 0.02 0.017 100 m 0.04 表 3 轨迹精度对比(m)
场景 指标 方法 FAST-LIO2 Faster-LIO Slice-SLAM (无回环) FAST-LIO-SAM Faster-LIO-SC Slice-SLAM (有回环) 仿真场景 MAXE 29.043 15.884 13.025 6.487 3.502 3.173 MAE 2.625 1.999 1.672 1.846 1.472 1.401 RSME 3.842 1.445 1.131 0.730 0.656 0.632 HME 1.181 0.646 0.530 0.264 0.143 0.129 真实场景 MAXE 35.694 26.014 17.234 28.008 23.501 10.812 MAE 13.598 8.808 6.268 10.261 8.137 5.215 RSME 7.185 6.581 3.753 5.010 5.855 2.443 HME 0.972 0.708 0.469 0.763 0.639 0.294 表 2 语义提取运行效率(FPS)
方法 单帧帧率 3帧帧率 5帧帧率 RANSAC 14.388 11.990 10.010 Region Growth 5.376 1.001 0.529 3D_SEG 4.274 1.458 0.740 本文 211 112.104 62.893 表 4 语义提取运行效率(FPS)
方法 单帧帧率 5帧帧率 10帧帧率 RANSAC 9.215 8.456 7.450 Region Growth 1.993 0.722 0.345 3D_SEG 3.425 1.276 0.309 本文 206.267 95.950 32.660 表 5 回环检测结果对比
指标 方法 ICP NDT GICP Fast_GICP Quatro Scan_Context + ICP 本文 0~2 m 运行时间(s) 0.817271 0.735771 0.364556 0.336739 0.166818 0.422534 0.245286 置信分数 0.113421 0.513051 0.107523 0.115033 2.470698 0.111862 0.108105 4~6 m 运行时间(s) 0.760850 0.961706 0.379740 0.374925 0.169581 0.453751 0.250143 置信分数 0.129462 0.452106 0.117008 0.112414 2.587779 0.116497 0.110242 8~10 m 运行时间(s) 0.783931 0.863472 0.448796 0.333281 0.174932 0.465473 0.264625 置信分数 0.128523 0.581624 0.114952 0.114824 2.909427 0.114505 0.113278 -
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