Researchers interested in spatial query processing in wireless sensor networks (WSNs) and query processing in spatial and geographical databases should include this paper in their reference lists.

Instead of providing a superficial, general survey, the authors insightfully capture the key characteristics of the details in this field. For example, in the beginning, the authors point out the two major differences between spatial and traditional queries.

One of the most important challenges in WSN processing lies in the messaging protocol used by the nodes within the network, where the goal is to save as much energy as possible because of the energy and resource constraints in WSNs. Based on this knowledge, the authors divide the entire query processing procedure into six stages: preprocessing, forwarding, dissemination, sensing, aggregation, and return.

A brief introduction to each stage is given first to illustrate the big picture of the entire field of spatial query processing in WSNs. For each stage, the authors conduct an in-depth investigation of the algorithms used and their most important properties. For example, in the forwarding stage, the algorithms covered include flooding, the greedy protocol, greedy perimeter stateless routing (GPSP), and spatial query routing (SQR).

This work also covers the processing mechanisms for two different spatial queries, the window query and the k nearest neighbors (KNN) query. Finally, the utilization of information fusion in this topic and future research opportunities are elaborated.

This paper is rich with details of spatial query processing in WSNs and will be beneficial to those in many related fields.