Distributed In-memory Trajectory Similarity Search and Join on Road Network

With the Widespread use of Internet of Thing (IoT) technology and the extensive application of wireless communication technologies, innovational changes have been made in all walks of life. In the field of navigation, Automatic Identification System (AIS) is widely equipped in vessels, which can obtain continuous position data from vessels and assemble them to vessel trajectories. While the massive vessel trajectory data obtained through AIS make great difficulty in maritime data analysis, however, they also make the vessel trajectory similarity measure become a hot topic in spatial database research. In recent years, there have been many studies about trajectory similarity measure of maritime, but these methods only consider the calculation of relative position between trajectory points, and these methods are inefficient with a low accuracy of trajectory similarity measure. In this study, we propose a novel approach called Convolutional Autoencoder (CAE), for measuring vessel trajectory similarity based on Convolutional Neural Network (CNN) and Autoencoder (AE). In this model, the vessel trajectory was gridded, and the grid-based Convolutional Autoencoder was proposed to extract the trajectory data as feature vectors to represent the original trajectories. Then the low-dimensional feature vectors were used for estimating the original trajectory similaiity. In addition, an experiment was conducted to prove the effectiveness of our model. Compared with the Frechet distance and Dynamic Time Warping (DTW)distance with the CAE, the results prove that CAE is capable of more efficient trajectory similarity computation and search.

Urban Foundation Models (UFMs) are emerging as a transformative paradigm for understanding and managing complex urban systems, offering new capabilities to improve and transform urban environments. Trajectory data (e.g., vehicle movements) contains rich spatio-temporal patterns of human mobility and urban dynamics that are crucial for understanding city-wide movement behaviors, traffic patterns, and transportation system operations. Effectively modeling such trajectory data is crucial for UFMs, yet this poses significant challenges due to the high-dimensional nature of raw trajectories and their complex spatio-temporal dynamics. Trajectory representation learning addresses these challenges by transforming raw trajectory data into compact, meaningful representations that capture essential mobility patterns and facilitates the application to various urban tasks, such as trajectory similarity computation, travel time estimation, or destination prediction. This is achieved by learning low-dimensional representations from high-dimensional and raw trajectory data. However, existing methods for trajectory representation learning either rely on grid-based or road-based representations, which are inherently different and thus, could lose information contained in the other modality. Moreover, these methods overlook the dynamic nature of urban traffic, relying on static road network features rather than time-varying traffic patterns. In this paper, we propose TIGR , a novel model designed to integrate grid and road network modalities while incorporating spatio-temporal dynamics to learn rich, general-purpose representations of trajectories. We evaluate TIGR on three real-world datasets and demonstrate the effectiveness of combining both modalities by substantially outperforming state-of-the-art methods, i.e., up to 59.34% for trajectory similarity, up to 16.65% for travel time estimation, and up to 14.81% for destination prediction.

Dynamic trajectory partition optimization method based on historical trajectory data

The market for on-demand mobility services is growing worldwide. These services include, for example, ride-hailing, ride-sharing, and car-sharing. Large-scale fleets of such services collect GPS trajectory (probe vehicle) data constantly everywhere in the network. At a certain penetration rate, this data becomes representative of the entire road network. It can give valuable insights into traffic dynamics and the evolution of congestion. In this paper, we use such GPS trajectory data from Chengdu, China, to investigate the stability and recurrence of macroscopic traffic patterns. Using the two-fluid theory, we find that the two-fluid coefficients are robust on between-day variation, not only supporting the theory itself but also emphasizing that the general evolution of traffic is a robust pattern. We investigate the deviations from the model using time series analysis of the residuals of the two-fluid model. Here, we find evidence for daily and weekly seasonality in the residuals, indicating that congestion patterns are convincingly recurring. These patterns can be used for network-wide traffic state prediction. We conclude that GPS trajectory data from large on-demand mobility fleets is a promising data source for observing traffic patterns in urban road networks once the data becomes representative.

In this paper, we propose a new spatio-temporal similarity measure to compute spatio-temporal relevance between two trajectories of moving objects on road networks, which is known as spatio-temporal distance (STDist). In addition, we provide a similar trajectory search algorithm to retrieve similar trajectories based on the proposed measure i.e., a combination of both spatial and temporal properties with respect to the motion of a given query trajectory. The performance evaluation shows that our approach outperforms the existing work in terms of searching similar trajectories of moving objects on road networks.

The analysis of large-scale trajectory data has tremendous benefits for applications ranging from transportation planning to traffic management. A fundamental building block for the analysis of such data is the computation of similarity between trajectories. Existing work for similarity computation focuses mainly on the spatial aspects of trajectories, but more rarely takes into account time in conjunction with space. A key challenge when considering time is how to handle trajectories that are sampled asynchronously or at variable rates, which can lead to uncertainty. To tackle this problem, we quantify trajectory similarity as an interval, rather than a single value, to capture the uncertainty that can result from different sampling rates and asynchronous sampling. Based on this perspective, we develop a new trajectory similarity measure, Trajectory Interval Distance Estimation, which models similarity computation as a convex optimisation problem. Using two real datasets, we demonstrate that our proposed measure is extremely effective for assessing similarity in comparison to existing state of the art measures.

Mobility data of a moving object, called trajectory data, are continuously generated by vessel navigation systems, wearable devices, and drones, to name a few. Trajectory data consist of samples that include temporal, spatial, and other descriptive features of object movements. One of the main challenges in trajectory data analysis is to divide trajectory data into meaningful segments based on certain criteria. Most of the available segmentation algorithms are limited to processing data offline, i.e., they cannot segment a stream of trajectory samples. In this work, we propose an approach called Reactive Buffering Window - Trajectory Segmentation (RBW-TS), which partitions trajectory data into segments while receiving a stream of trajectory samples. Another novelty compared to existing work is that the proposed algorithm is based on multidimensional features of trajectories, and it can incorporate as many relevant features of the underlying trajectory as needed. This makes RBW-TS general and applicable to numerous domains by simply selecting trajectory features relevant for segmentation purposes. The proposed online algorithm incurs lower computational and memory requirements. Furthermore, it is robust to noisy samples and outliers. We validate RBW-TS on three use cases: (a) segmenting human-movement trajectories in different modes of transportation, (b) segmenting trajectories generated by vessels in the maritime domain, and (c) segmenting human-movement trajectories in a commercial shopping center. The numerical results detailed in the paper demonstrate that (i) RBW-TS is capable of detecting the true breakpoints of segments in all three usecases while processing a stream of trajectory points; (ii) despite low memory and computational requirements, the performance in terms of the harmonic mean of purity and coverage is comparable to that of state-of-the-art batch and online algorithms; (iii) RBW-TS achieves different levels of accuracy depending on the various internal parameter estimation methods used; and (iv) RBW-TS can tackle real-world trajectory data for segmentation purposes.

Nowadays, most vehicles are equipped with positioning devices such as GPS which can generate a tremendous amount of trajectory data and upload them to the server in real time. The trajectory data can reveal the shape and evolution of the road network and therefore has an important value for road planning, vehicle navigation, traffic analysis, and so on. In this paper, a road network generation method is proposed based on the incremental learning of vehicle trajectories. Firstly, the input vehicle trajectory data are cleaned by a preprocess module. Then, the original scattered positions are clustered and mapped to the representation points which stand for the feature points of the real roads. After that, the corresponding representation points are connected based on the original connection information of the trajectories. Finally, all representation points are connected by a Delaunay triangulation network and the real road segments are found by a shortest path searching approach between the connected representation point pairs. Experiments show that this method can build the road network from scratch and refine it with the input data continuously. Both the accuracy and timeliness of the extracted road network can continuously be improved with the growth of real-time trajectory data.

The transport of hazardous materials can have a negative impact on human health and the environment quality; therefore it represents a relevant concern for each national economy of Europe. In Italy, the Apulia Region funded a research project to face this problem. In this framework, the authors proposed a flexible intelligent transport system (ITS) designed to work in many complex situations on the road network. This ITS uses artificial intelligence methods to implement route planning. Essentially, the system specifies a route for each vehicle by optimising a multi-objective function. The objectives, which are optimised, depend on the specific application and in this work they are related to the hazardous material transport impact reduction. This goal is achieved by implementing a negotiation process among intelligent agents. The system monitors the route followed by each vehicle and verifies if it coincides with the specified route. A key element of the ITS is a flexible on-board unit mounted on vehicles. It has a modular structure that allows for a variety of sensors to be connected, depending on the application. In this case, a variety of parameters, such as the vehicle speed, position, load balance and accelerations are analysed. Using that data the system identifies some characteristics, for example, the driver behaviour and hazardous vehicle operating conditions. In order to represent this information, the authors propose a multi-level metaphor-based graphic user interface (GUI). The first level of the interface provides a quickly understood view of the situation being monitored and it is oriented towards on-site first response and route monitoring operators. The second level provides more detailed information for incident managers and other operators. This interface has been evaluated using a human panel. Each volunteer has compiled a questionnaire after that he/she has used the interface for a 30-min session. The focus of this work is to present the approaches adopted for route planning and the user interface.

With the rapid development of digital technologies, location-aware technologies have helped increase trajectory data availability that results from tracking moving objects. Through the collection and analysis of trajectory data, the extracted knowledge can be beneficial in many applications. Trajectories are widely known as a series of points that represent geographic locations. The researchers devoted their efforts to many trajectory data mining fields, where the benefit of these data can be gained and employed in many applications. This paper focuses on providing a comprehensive review of trajectory data mining applications such as path detection, urban services, environment services, objects behavior analysis, and so on.

Up to now, a large amount of trajectory data have been collected by trusted servers because of the wide use of location-based services. One can extract useful information via an analysis of trajectory data. However, the privacy of trajectory bodies risks being inadvertently divulged to others. Therefore, the trajectory data should be properly processed for privacy protection before being released to unknown analysts. This paper proposes a privacy protection scheme for publishing the trajectories with personalized privacy requirements based on the translocation of trajectory points. The algorithm not only enables the published trajectory points to meet the personalized privacy requirements regarding desensitization and anonymity but also preserves the positions of all trajectory points. Our algorithm trades the loss in mobility patterns for the advantage in the similarity of trajectory distance. Related experiments on trajectory data sets with personalized privacy requirements have verified the effectiveness and the efficiency of our algorithm.

Spatial-temporal trajectory data is a position sequence recording the time and space of moving objects. It is the most important data source for the study of moving objects. The analysis and mining of spatial-temporal trajectory data is a research hotspot of spatial data mining. In the process of analysis and mining, the similarity measurement between trajectories is a key problem. This paper studies the spatial-temporal trajectory similarity measurement algorithms, selects the trajectory similarity measurement algorithms based on Hausdorff distance and One Way distance as the research object, and sets three comparative experiments on the execution time, robustness and trajectory similarity discrimination effect of different location relations of the algorithm. Through the experimental results, the advantages, disadvantages and application occasions of the two algorithms are analyzed, It provides a reference for spatial-temporal trajectory analysis and mining.

The prevalence of GPS applications and other mobile devices has led to the accumulation of a large amount of trajectory data that contains valuable information for intelligent transportation, route planning, city computing etc. However, massive data not only brings new challenges to data storage and retrieval but also leads to serious privacy risks because of the abundant spatiotemporal information. In this paper, we propose a storage scheme that strikes a balance between the compression ratio and precision. We then introduce a road segment generalization method to address privacy issues stemming from sensitive places. Next, we design a two-layer index mechanism to provide an effective retrieval. Furthermore, a privacy preserving storage system PP-TrajStore is implemented. It provides efficient storage based on a road segment compression scheme, preserves privacy by employing sensitive segment generalization technologies, and achieves rapid retrieval by a two-layer index strategy. Finally, a realworld dataset is utilized to demonstrate the performance of PP-TrajStore

In a cloud environment, resources should be acquired quickly and automatically released at runtime. Traditional trajectory data partitions, indexing and query processing techniques are extended, so that they can take advantage of the cloud of large clusters of highly parallel processing capabilities. There are ways with trajectory data in the cloud database query processing. The advanced sensing techniques available today caused the existence of many types of trajectory datasets whose study can form a strong basis for decision making regarding a data context. Trajectory data generally includes trajectory classification, trajectory clustering, and trajectory associations and so on. All these tools need trajectory similarity measures to get comparisons in trajectory data. Some of the popular existing methods of trajectory similarity include Euclidean distance, semantic distance and there near variants. Each variant of these techniques exhibits notable differences in measurement of similarity and computational difficulty. This paper targeted to deal with this situation with the goal of lower computational efforts in trajectory similarity computations. A two‐phase trajectory similarity measure is defined. The first phase does point level analysis of trajectory points representing all trajectories and the following phase use the analysis to find the similarities. Using a hybrid similarity framework, new means for trajectory clustering and trajectory query processing are developed. From trajectory analysis followed by trajectory clustering, evaluation of cluster quality and processing of trajectory query are undertaken in this paper in different ways from the existing methods. All the proposed developments are tested with trajectory datasets with multiple attributes and the results are more favour to proposed framework than the existing ones.

Efficient Path Routing Over Road Networks in the Presence of Ad-Hoc Obstacles