Journal of Geo-information Science >
A Fast Method of FCD Trajectory Data Clustering Based on the Directed Density
Received date: 2015-04-20
Request revised date: 2015-05-18
Online published: 2015-10-10
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Floating car data (FCD), which is the trajectories of vehicles, are automatically collected by huge quantities of commercial vehicles which are equipped with GPS devices. Exploring and exploiting such data is essential to understand the dynamic aggregation patterns of trajectory data. However, the existing methods of spatial density clustering mainly focus on undirected data, and it is difficult to effectively find the characteristics of trajectory data. We contribute to the literatures on FCD trajectory data mining by presenting a novel method called directed density clustering method (D-OPTICS), which is formulated based on the spatial density clustering algorithm (OPTICS). In our method, the directed density is computed by a fan-shaped neighborhood region, and the density connectivity is restrained by its direction information. Then, the base clusters are generated using the curve analysis of reachable distance. Finally, the D-OPTICS cluster method is formed by the optimization method of spatial grid and cluster polymerization. This method can be naturally applied to FCD trajectory data mining, and it is also appropriate for handling other directed spatial data. It can be employed to discover the spatio-temporal distribution characteristic of traffic trajectory, and then be adopted to extract the structure information of complex road network. The experiments, with massive floating car data of Fuzhou city, show that the D-OPTICS can cluster directed spatial data effectively, and is useful to uncover the inherent distribution characteristic of the massive trajectory data. Based on its clustering result, the topology information of road network can be extracted. In this work, we extracted the topology graph for the complex road network of Fuzhou city. The experiment results also show that the algorithm can automatically determine the number of clusters, and it is found that the algorithm is not limited to globular cluster data and is capable to deal with clusters of arbitrary shapes. The key contribution of this method is that it takes the direction information into account and it can also be effective in reducing the problems caused by traditional clustering algorithms which may incorrectly merge or decompose thus naturally produce large clusters and noise data. Meanwhile, the result of performance experiments shows that, compared with DBSCAN and OPTICS, the proposed method is more suitable for large-scale data processing.
LIAO Lvchao , JIANG Xinhua , ZOU Fumin , LI Luming , LAI Hongtu . A Fast Method of FCD Trajectory Data Clustering Based on the Directed Density[J]. Journal of Geo-information Science, 2015 , 17(10) : 1152 -1161 . DOI: 10.3724/SP.J.1047.2015.01152
Fig. 1 Directed directly density-reachable图1 直接有向密度可达 |
Fig. 2 The diagram of directed connected-density图2 有向密度相连示意图 |
Tab. 1 FCD trajectory data based on directed density by D-OPTICS algorithm表1 基于有向密度的浮动车轨迹数据聚类D-OPTICS算法 |
输入: 浮动车轨迹数据集 输出: 不同道路、不同车道的浮动车轨迹数据簇 |
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步骤1: 按精度要求建立空间网格,并将数据按网格划分为数据子集; repeat { 步骤2: 结合轨迹数据方向区间信息,并将数据集gi划分为数据子集; repeat { 步骤3: 选取一个数据子集,计算其核心距离和可达距离次序图rdi; } until 完成所有方向区间的计算,方向值从大到小拼合成整个数据集的可达距离图 步骤4: 根据可达距离的峰值变化生成基本簇; 步骤5: 根据道路方向变化的渐变性原则,基于凝聚层次聚类的思想,合并方向变化较小且存在共同边界粘合点的基本簇,进而得到最终的簇划分; } until 完成所有网格数据子集的计算 |
Fig. 3 The diagram of FCD trajectory data based on directed density图3 浮动车轨迹数据有向密度图 |
Fig. 4 The diagram of reachable distance sequence图4 可达距离序列示意图 |
Fig. 5 The statistical chart of direction data图5 方向数据统计图 |
Fig. 6 The image of spatial information grid图6 空间信息网格图 |
Fig. 7 The image of polymeric road network (for Fuzhou city)图7 交通路网聚合图(福州市) |
Fig. 8 The diagram of directly reachable distance (single grid)图8 有向可达距离图(单网格) |
Fig. 9 The diagram of clustering based on D-OPTICS algorithm图9 D-OPTICS聚类效果图 |
Fig. 10 Comparison of the resultant clustering effects between D-OPTICS, DBSCAN and OPTICS algorithms图10 D-OPITCS与DBSCAN、OPTICS算法聚类效果对比图 |
Fig. 11 The diagrams of clustering based on D-OPTICS algorithm图11 D-OPITCS算法聚类效果图 |
Fig. 12 The diagrams of new road detection experiment图12 新增道路检测实验图 |
Fig. 13 The road network topology of Fuzhou urban area图13 福州市区路网拓扑结构图 |
Tab. 2 The comparison of algorithms’ performance表2 算法性能测试对比表 |
序号 | 样本量(个) | 邻域半径(m) | MinPts | DBSCAN | OPTICS | D-OPTICS |
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1 | 5000 | 100 | 10 | 2.14 | 5.73 | 4.31 |
2 | 10 000 | 50 | 20 | 4.66 | 13.81 | 9.63 |
3 | 50 000 | 10 | 20 | 34.86 | 93.56 | 63.29 |
4 | 100 000 | 10 | 20 | 214.51 | 221.31 | 136.79 |
5 | 500 000 | 10 | 20 | 2216.42 | 1286.36 | 739.18 |
The authors have declared that no competing interests exist.
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