Abstract. In this paper, we describe a novel camera calibration method to estimate the extrinsic parameters and the focal length of a camera by using only one single image of two coplanar circles with arbitrary radius.We consider that a method of simple operation to estimate the extrinsic parameters and the focal length of a camera is very important because in many vision based applications, the position, the pose and the zooming factor of a camera is adjusted frequently.An easy to use and convenient camera calibration method should have two characteristics: 1) the calibration object can be produced or prepared easily, and 2) the operation of a calibration job is simple and easy. Our new method satisfies this requirement, while most existing camera calibration methods do not because they need a specially designed calibration object, and require multi-view images. Because drawing beautiful circles with arbitrary radius is so easy that one can even draw it on the ground with only a rope and a stick, the calibration object used by our method can be prepared very easily. On the other hand, our method need only one image, and it allows that the centers of the circle and/or part of the circles to be occluded.Another useful feature of our method is that it can estimate the focal length as well as the extrinsic parameters of a camera simultaneously. This is because zoom lenses are used so widely, and the zooming factor is adjusted as frequently as the camera setting, the estimation of the focal length is almost a must whenever the camera setting is changed. The extensive experiments over simulated images and real images demonstrate the robustness and the effectiveness of our method.

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In the paper recent design and tuning methods of PID controllers are summarized briefly. Several decades have seen the widely application of PID controllers and the design and tuning methods have been of considerable development. Process model identification, PID controller structure design, PID parameters tuning methods and the use and expansions of PID are described in turn. PID parameter tuning methods are highlighted.

The range measurement is the premise for location, and the precise range measurement is the assurance of accurate location. Hence, it is essential to know the accurate internode distance. It is noted that the path loss model plays an important role in improving the quality and reliability of ranging accuracy. Therefore, it is necessary to investigate the path loss model in actual propagation environment. Through the analysis of experiments performed at the wheat field, we find that the best fitted parametric exponential decay model (OFPEDM) can achieve a higher distance estimation accuracy and adaptability to environment variations in comparison to the traditional path loss models. Based on the proposed OFPEDM, we perform the RSSI-based location experiments in wheat field. Through simulating the location characteristics in MATLAB, we find that for all the unknown nodes, the location errors range from 0.0004 m to 5.1739 m. The location error in this RSSI-based location algorithm is acceptable in the wide areas such as wheat field. The findings in this research may provide reference for location estimation in large-scale farmland.