Location Update Strategies for Network-Constrained Moving Objects
Location update strategy is one of the most important factors that affect the performance of moving objects databases. In this paper, a new location update mechanism, Location Update Mechanism for Network-Constrained Moving Objects (Net-LUM), is proposed.
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Abstract. Location update strategy is one of the most important factors that affect the performance of moving objects databases. In this paper, a new location update mechanism, Location Update Mechanism for NetworkConstrained Moving Objects (Net-LUM), is proposed. Through active-motionvector-based network-matching and special treatment with junctions, Net-LUM can achieve better performances in terms of communication costs and location tracking accuracy, which is confirmed by the experimental results. Keywords: Database, Spatiotemporal, Moving Object, Location Update.
1 Introduction Moving Objects Database (MOD) is the database that can track and manage the locations of moving objects such as cars, ships, flights, and pedestrians. One of the key problems with MOD is to continuously track the locations of moving objects with minimum communication and computation costs. To answer location related queries, the server has to know the current and the historical location information of all registered moving objects, which means that the location information at the server has to be refreshed through location update messages sent by the moving objects. There exist a large number of location-tracking mechanisms in the literature, and there are also several practical (and simpler) solutions adopted by real-world applications [4, 5, 6, 1]. In general, these methods can be divided into three categories: Fixed-Time Location Update Mechanisms (FTLU), Fixed-Distance Location Update Mechanisms (FDLU), and Motion-Vector-Based Location Update Mechanisms (MVBLU). Currently, FTLU and FDLU are widely used in real-world systems because of their simplicity. However, in terms of efficiency and accuracy, FTLU and FDLU are not the best choices, and as a result, MVBLU has become increasingly influential in the MOD area [4, 6]. In [5, 6], Wolfson et. al. have proposed a location update mechanism which can utilize the geometry of routes and the topology of the traffic network. In their method, however, only distance/deviation triggered location updates are defined so that when the moving object transfers from one route to another the change can not be reported J.R. Haritsa, R. Kotagiri, and V. Pudi (Eds.): DASFAA 2008, LNCS 4947, pp. 644–652, 2008. © Springer-Verlag Berlin Heidelberg 2008
Location Update Strategies for Network-Constrained Moving Objects
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to the server promptly, which can affect the accuracy of location tracking. In [1], Civilis and Jensen et al. have proposed a road-network-based location tracking mechanism for moving objects. However, their method heavily depends on GPS logs in linking segments into routes and in generating accelerating profiles, which limits its usability in real-world applications. In [2], Ding and Güting have proposed an MODTN model and provided some rough location update principles for network constrained moving objects. However, the method is based on mile-meters and a lot of key problems, such as network-matching, junction treatment, detailed algorithms, and performance evaluation, remain unsolve
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