Indexing Objects Moving on Fixed Networks

Indexing Objects Moving on Fixed Networks - Indexing...

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Unformatted text preview: Indexing Objects Moving on Fixed Networks Elias Frentzos Department of Rural and Surveying Engineering, National Technical University of Athens, Zographou, GR-15773, Athens, Hellas efrentzo@central.ntua.gr Abstract. The development of a spatiotemporal access method suitable for ob- jects moving on fixed networks is a very attractive challenge due to the great number of real-world spatiotemporal database applications and fleet manage- ment systems dealing with this type of objects. In this work, a new indexing technique, named Fixed Network R-Tree (FNR-Tree), is proposed for objects constrained to move on fixed networks in 2-dimensional space. The general idea that describes the FNR-Tree is a forest of 1-dimensional (1D) R-Trees on top of a 2-dimensional (2D) R-Tree. The 2D R-Tree is used to index the spatial data of the network (e.g. roads consisting of line segments), while the 1D R- Trees are used to index the time interval of each objects movement inside a given link of the network. The performance study, comparing this novel access method with the traditional R-Tree under various datasets and queries, shows that the FNR-Tree outperforms the R-Tree in most cases. 1 Introduction Most recently developed spatiotemporal access methods (3D R-Tree [16], HR-Tree [6, 7], TB-Tree, STR-Tree [10], TPR-Tree [13], Mv3R-Tree [14], PPR-Tree [3]) are designed to index objects performing any kind of movement in a two-dimensional space. These methods are general and do not take into consideration the special re- quirements of the application in which they are used. However, in real-world applica- tions several conditions having to do with the demanded level of generalization and the way of perception of data, can improve the performance of the spatiotemporal in- dexes. For example, in a research for the emigrational habits of some animal popula- tion (dolphins, whales e.t.c.), more likely is that the precise position of each separate animal is not of interest, but the region in which is contained the population. This can lead to dramatic reduction of the number of moving objects that should be indexed by an indexing technique, and to the consequently increase of its performance. Another condition that can be used to improve the performance of spatiotemporal indexes is the existence of restrictions in the space in which moving objects realize their movement. Although the vast majority of spatiotemporal access methods index objects moving in the whole of the two dimensional space, in most real-world applications the objects are moving in a constrained space: planes fly in air-paths, cars and pedestrians move on road networks, while trains have fixed trajectories on railway networks. These kind of special conditions (moving restrictions) have recently been subject of the researching interest [5, 8, 9, 11]. As it is obvious, the development of a spatiotemporal access method suitable for objects moving on fixed networks is a very attractive challenge because a great num-...
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Indexing Objects Moving on Fixed Networks - Indexing...

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