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In order to analyze the behavior of moving objects, a measure for determining the similarity of trajectories needs to be defined. Although research has been conducted that retrieved similar trajectories of moving objects in Euclidean space, very little research has been conducted on moving objects in the space defined by road networks. In terms of real applications, most moving objects are located in road network space rather than in Euclidean space. In this paper, we investigate the properties of similar trajectories in road network space. And we propose a method to retrieve similar trajectories based on this observation and similarity measure between trajectories on road network space. Experimental results show that this method provides not only a practical method for searching for similar trajectories but also a clustering method for trajectories.

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Abstract. In order to search similar moving object trajectories, the previously used methods focused on Euclidean distance and considered only spatial similarity. Euclidean distance is not appropriate for road network space, where the distance is limited to the space adjacent to the roads. In this paper, we consider the properties of moving objects in road network space and define temporal similarity as well as spatio-temporal similarity between trajectories based on POI (Points of Interest) and TOI (Times of Interest) on road networks. Based on these definitions, we propose methods for searching for similar trajectories in road network space. Experimental results show the accuracy of our methods and the average search time in query processing.

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Metasurface-based optical cavity structures consist of a metallic metasurface realized on top of a dielectric slab backed with a metal plane. Such structures have been employed in the design of optical devices such as flat lenses, wave plates, and holograms at frequencies from microwave to mid-infrared. Recently, such structures with dynamically reconfigurable optical characteristics have been explored for electrically tunable optical absorption and reflection phase modulation. To date, absorption modulation and phase modulation have been realized with large insertion loss. In this work, we employ an analytical approach based on transmission line theory where the metasurface is represented by a surface admittance. We extend the above approach for the design and analysis of under-and overcoupled resonance regimes in the metasurface cavity structure. This enables a mutual design of cavity thickness and individual metasurface for large amplitude or phase modulation. A dynamic-metasurface-based optical cavity is experimentally demonstrated at terahertz frequencies where the dynamic metasurface consists of metallic resonators embedded with thin-film vanadium dioxide patches. By driving an insulator to metal transition in vanadium dioxide, the terahertz optical response of the metasurface-based cavity structure is modulated. The fabricated device exhibits perfect absorption modulation and reflection phase modulation up to 180°. The reported results demonstrate the potential of such structures for realizing novel devices such as tunable holograms, high-efficiency modulators, and frequency-tunable filters at terahertz. The analytical approach presented here can be applied to the analysis and design of metasurface cavity structures based on other material systems at frequencies ranging from terahertz to mid-infrared.

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