Spatial identification of the urban-rural fringes is very significant for deeply understanding the development processes and regulations of urban space and guiding urban spatial development in the future. Traditionally, urban-rural fringe areas are identified using statistical analysis methods that consider indexes from single or multiple factors, such as population densities, the ratio of building land, the proportion of the non-agricultural population, and economic levels. However, these methods have limitations, for example, the statistical data are not continuous, the statistical standards are not uniform, the data is seldom available in real time, and it is difficult to avoid issues on the statistical effects from edges of administrative regions or express the internal differences of these areas. This paper proposes a convenient approach to identify the urban-rural fringe using nighttime light data of DMSP/OLS images. First, a light characteristics-combined value model was built in ArcGIS 10.3, and the combined characteristics of light intensity and the degree of light intensity fluctuation are analyzed in the urban, urban-rural fringe, and rural areas. Then, the Python programming language was used to extract the breakpoints of the characteristic combination values of the nighttime light data in 360 directions taking Tian An Men as the center. Finally, the range of the urban-rural fringe area is identified. The results show that the urban-rural fringe of Beijing is mainly located in the annular band around Tian An Men. The average inner radius is 19 km, and the outer radius is 26 km. The urban-rural fringe includes the outer portions of the four city center districts, which are the Chaoyang District, Haidian District, Fengtai District, and Shijingshan District and the part area border with Daxing District, Tongzhou District, Changping District, Mentougou District, Shunyi District, and Fangshan District. The area of the urban-rural fringe is approximately 765 km 2 . This paper provides a convenient, feasible, and real-time approach for the identification of the urban-rural fringe areas. It is very significant to extract the urban-rural fringes.
The majority of GPS applications will be in real time positioning. This paper presents the accuracies 0/ rela/ire kinematic positioning using Trimble 4000S receivers. A test network o/thlrteen stations/orming part o/the South Australian Geodetic SUfl'e.V was used/or the experiment carried out in August 1988. IntroductionThe Global Positioning System (GPS) is an all-weather. space-borne navigational system. It is being developed in stages by the U.S. Department of Defense (DoD). Wells (1986) indicated that the accuracy of real time or kinematic positioning using the GPS Precise or P code is of the order of 15 to 20 m () sigma). The corresponding accuracy with the Coarse Acquisition of CIA code is between 20 to 30 m (I sigma). For civil users who need better real time pmitioning accuracies. the technique of relative kinematic positioning. or differential positioning as it is commonly termed, is a viable option.The concept of differential G PS has been described by Oeser et aI, (1981) and Black well II 985). The basic idea consists of a fixed reference station which acts as a calibrator for the positioning system. The validity of differential GPS is based on the assumption that biases at the reference and user positions are common for a specific distance between them and time. Its accuracy is limited by the receiver noise. inter·channel biases and reference station uncertainty.There are two obvious methods of improving the user position with corrections provided by the reference station. The direct method would be to apply the co-ordinate differences between the known and computed position values at the reference station to the user's observed position.Simultaneous observations to the same set of satellites at both the fixed and roving stations are neces!>ary. Alternatively, the differences between the observed and computed pseudo-ranges at the reference station are applied to the observed pseudo ranges at the user station to derive an improved position.
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