This article presents the development of an image-based sun position sensor and the algorithm for how to aim at the Sun precisely by using image processing. Four-quadrant light sensors and bar-shadow photo sensors were used to detect the Sun's position in the past years. Nevertheless, neither of them can maintain high accuracy under low irradiation conditions. Using the image-based Sun position sensor with image processing can address this drawback. To verify the performance of the Sun-tracking system including an image-based Sun position sensor and a tracking controller with embedded image processing algorithm, we established a Sun image tracking platform and did the performance testing in the laboratory; the results show that the proposed Sun tracking system had the capability to overcome the problem of unstable tracking in cloudy weather and achieve a tracking accuracy of 0.04°.

Neo4j database based on graph model is different from other database on implementation.Firstly, this paper explores the architecture of the system and its internal mechanism.Secondly, Neo4j offers three ways to query, and evaluate its query performance from several dimensions: data size, query complexity, query number, etc. The results show that there are obvious difference in performance under different scenarios. This paper analyzes the experimental results and selection suggestions of query ways are recommended later. It provides a reference of query performance optimization for specific business applications.

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