Ship trajectory compression method based on time ratio-speed-heading
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摘要: 考虑船舶航迹中包含的时间、位置、航速与航向等信息,提出一种全面考虑时空运动特性的船舶轨迹压缩方法;针对船舶自动识别系统(AIS)数据中的对地航速和对地航向分别提出航速及航向压缩算法以提取轨迹运动数据;为保留时间信息和空间数据,引入时间比率算法;通过综合这3种算法,提出时间比率-航速-航向(TSH)压缩算法,并根据压缩率和长度损失率实现了TSH算法参数的自适应确定;为验证方法的有效性,以威海、老铁山和长江水域的AIS数据作为研究对象,与道格拉斯-普克(DP)算法、改进DP算法进行对比。试验结果表明:TSH算法能够更精细地提取船舶轨迹的特征点,从而保留时空和运动行为,其中,单条轨迹压缩结果显示,经TSH算法压缩后的轨迹与原始轨迹之间的豪斯多夫距离比DP算法和改进DP算法分别降低1.6和1.1倍,多属性对称分割路径距离(MSSPD)较改进DP算法降低1.9倍,更好地保留了船舶轨迹的原始特征;整体轨迹压缩结果显示,对于威海、老铁山和长江水域,TSH算法在豪斯多夫距离上较DP算法分别降低2.1、2.2和1.7倍,较改进DP算法分别降低1.4、1.5和1.1倍,在MSSPD指标上分别低于改进DP算法1.3、1.1和1.2倍,进一步证明TSH压缩算法对船舶航行行为保留的有效性。经验证,所提出的TSH算法在较高压缩率下展现出更好的轨迹重构能力。Abstract: By considering that the ship trajectory contains information such as time, position, speed, and heading, a ship trajectory compression method considering the spatiotemporal motion characteristics was proposed. For the ground speed and ground heading in the automatic identification system (AIS) data of ships, the speed-based (SP) and the heading-based (HD) compression algorithms were proposed to extract the trajectory motion data. To retain the time information and spatial data, the time-ratio (TR) algorithm was introduced. By integrating these three types of algorithms, the time ratio-speed-heading (TSH) compression algorithm was proposed, and the parameters of the TSH algorithm were adaptively determined according to the compression rate and length loss rate. To verify the effectiveness of proposed method, the AIS data of Weihai, Laotieshan, and Yangtze River waters were used as research objects and compared with the Douglas-Peucker (DP) algorithm and the improved DP algorithm. Experimental results show that the characteristic points of the ship trajectory can be more finely extracted by the TSH algorithm, thereby retaining the spatiotemporal and motion behavior. Among them, the single trajectory compression results show that the Hausdorff distance between the trajectories compressed by the TSH algorithm and the original trajectory is 1.6 and 1.1 times lower than those of the DP algorithm and the improved DP algorithm, respectively, and the multi-attribute symmetric segmentation path distance (MSSPD) is 1.9 times lower than that of the improved DP algorithm, which better retains the original characteristics of the ship trajectory. The overall trajectory compression results show that for Weihai, Laotieshan, and Yangtze River waters, the TSH algorithm is 2.1, 2.2, and 1.7 times lower than the DP algorithm in the Hausdorff distance and 1.4, 1.5, and 1.1 times lower than the improved DP algorithm, respectively. In the MSSPD index, it is 1.3, 1.1, and 1.2 times lower than the improved DP algorithm, respectively, which further proves the effectiveness of the TSH compression algorithm in retaining the ship navigation behavior. It is verified that the proposed TSH algorithm shows better trajectory reconstruction ability at a higher compression rate.
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表 1 原始AIS数据
Table 1. Original AIS data
轨迹点 纬度/(°) 经度/(°) 对地航速/kn 对地航向/(°) 1 36.572 8 122.827 9 13.4 11.3 2 36.574 3 122.828 3 13.4 11.5 3 36.575 8 122.828 6 13.4 11.8 32 37.099 2 122.864 8 13.8 3.1 33 37.100 7 122.864 7 13.7 359.4 34 37.102 2 122.864 9 13.8 3.3 35 37.103 8 122.864 8 13.7 3.0 40 37.114 4 122.865 2 13.6 359.4 41 37.115 9 122.865 1 13.6 3.2 表 2 压缩算法对比
Table 2. Comparison of compression algorithms
压缩算法 时间复杂度 空间复杂度 考虑时间 考虑形状 考虑航速 考虑航向 TSH O(n2) O(n) 是 是 是 是 DP O(n2) O(n) 否 是 否 否 改进DP O[n2+nlog2(n)] O[n+log2(n)] 否 是 是 是 SSTC O[n2+nlog2(n)] >O(n) 是 是 是 是 表 3 不同阈值下SP算法的压缩率
Table 3. Compression rates of SP algorithm under different thresholds
阈值/kn 0.05 0.10 0.15 0.20 压缩率/% 92.61 97.83 99.13 99.13 表 4 不同阈值系数下HD算法的豪斯多夫距离
Table 4. Hausdorff distances of HD algorithm under different threshold coefficients
阈值系数 1 2 3 4 5 6 7 8 豪斯多夫距离/106 m 1.404 1.404 1.404 1.404 1.404 2.107 2.107 2.107 表 5 不同压缩算法压缩结果对比
Table 5. Comparison of compression results of different compression algorithms
压缩算法 压缩率/% 豪斯多夫距离/m MSSPD/m TSH 83.48 7.022 4×105 1.016 3×107 DP 94.78 1.115 7×106 改进DP 82.17 7.854 3×105 1.929 0×107 表 6 预处理后船舶轨迹数据
Table 6. Ship trajectory data after pretreatment
水域 数据量 过滤后AIS数据 修复后AIS数据 威海 船舶数/条 47 47 轨迹点数/个 30 900 31 150 老铁山 船舶数/条 86 86 轨迹点数/个 67 482 67 981 长江 船舶数/条 272 272 轨迹点数/个 89 610 91 040 表 7 不同水域轨迹压缩结果
Table 7. Trajectory compression results in different waters
水域 压缩结果 TSH算法 DP算法 改进DP算法 威海 平均压缩率/% 85.49 96.10 84.77 总豪斯多夫距离/107 m 2.523 1 5.377 9 3.555 9 总MSSPD/108 m 2.982 2 3.865 2 老铁山 平均压缩率/% 92.19 98.60 91.68 总豪斯多夫距离/107 m 4.010 0 8.905 2 5.863 1 总MSSPD/108 m 4.486 1 4.972 0 长江 平均压缩率/% 86.67 96.81 80.39 总豪斯多夫距离/107 m 5.337 1 8.852 2 5.660 1 总MSSPD/109 m 2.345 3 2.859 3 -
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