# Algorithms for Nearest Neighbor Search on Moving Object Trajectories

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## Abstract

Nearest Neighbor (NN) search has been in the core of spatial and spatiotemporal database research during the last decade. The literature on NN query processing algorithms so far deals with either stationary or moving query points over static datasets or future (predicted) locations over a set of continuously moving points. With the increasing number of Mobile Location Services (MLS), the need for effective *k*-NN query processing over historical trajectory data has become the vehicle for data analysis, thus improving existing or even proposing new services. In this paper, we investigate mechanisms to perform NN search on R-tree-like structures storing historical information about moving object trajectories. The proposed (depth-first and best-first) algorithms vary with respect to the type of the query object (stationary or moving point) as well as the type of the query result (historical continuous or not), thus resulting in four types of NN queries. We also propose novel metrics to support our search ordering and pruning strategies. Using the implementation of the proposed algorithms on two members of the R-tree family for trajectory data (namely, the TB-tree and the 3D-R-tree), we demonstrate their scalability and efficiency through an extensive experimental study using large synthetic and real datasets.

## Keywords

nearest neighbor moving objects NN query processing on R-tree-like structures storing historical trajectories## Notes

### Acknowledgements

Research partially supported by the GeoPKDD (“Geographic Privacy-aware Knowledge Discovery and Delivery”) project funded by the European Community under FP6-014915 contract. Research grants by the Archimedes and Pythagoras EPEAEK II Programmes jointly funded by the European Community and the Greek Ministry of National Education and Religious Affairs are also acknowledged. We also thank the anonymous reviewers for providing valuable comments which improved the quality of the paper.

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