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The moving $$k$$k nearest neighbor (MkNN) query has been studied extensively. Most of the studies assume no obstacle in the space. However, obstacles like rivers, buildings and private properties commonly exist in the space, and one may need to go around the obstacles to reach his/her nearest neighbors. In this paper, we study the moving kNN query in obstructed space with no predefined query object trajectory. We take a safe region based approach to solve this problem. In particular, we propose a method to compute a safe region w.r.t. a data object. In this safe region, the query object can move freely, while the data object is kept in the query object's kNN set. By combining the safe regions of the data objects near the query object, we formulate an overall safe region where the query object's kNN set keeps stable. We propose an algorithm based on the safe regions to process the moving kNN query in obstructed space. Extensive experiments show that the proposed algorithm significantly reduces the communication and the computation costs for query processing. Our algorithm outperforms a baseline algorithm by up to two orders of magnitude under various settings.

A safe region based approach to moving KNN queries in obstructed space