GPS Elevation Fitting And Its Application In Highway Survey

GPS(Global Positioning System), an advanced navigation and poisoning technology was rised with the development of the modern science. As the technology with all-weather, high-precision measurement and automatic features, it has played as an increasingly important role in a wide range of high-precision measurents and comtrol network, control network of the cities, control network of the projects and control nerwork of mappings. Especially in the projects with a long range and variable terrain, because of the reduction of the labor and the improvement of the efficiency and accuracy, GPS was proved to be better than conventional measurements. Presently the accuracy in the location of the plane is high enough to meet the requirments of many control planes with the utilizing of GPS. As the difference of the elevation system between the GPS and the practice, the study of the GPS fitting system is significant to make the GPS be used widely.Because of the inconsistency of GPS and leveling elevation system, GPS elevation need to be conveted to the elevation system that can be applied in engineering. This paper mainly focuses on several widely used GPS elevation fitting models. The basic principle of GPS measurement is introduced firstly, the factors which affect the accuracy of the convertion of GPS elevation are analysed later and then the common approaches and methods of GPS covertion are presented in detail as well as the robust eatimation method is introduced in the pre-processing of the GPS data, consequently the reliability of the elevation is improved dramatically. Finally in the case of the highway between Liuyang and Liling, the fitting models metioned above are compared and analysed and the result showes that in a specific narrow and long zonal area the orthogonal function model is the best model. Meanwile in the case of the highway between the Rucheng and Yanling , the high precision GPS elevations which were used in the refinement of the quasi-geoid of eastern and central China are ultilized. A good result is generated and further demonstrates the efficiency and accuracy of the elevation fitting in a narrow and long zonal area with the orthogonal function model. Other several projects with different topography are texted, concluded that the orthogonal function model are the best model for elevation fitting in narrow and long zonal areas.In order to satisfying the needs of the practices, a GPS elevation system combining the key techniques of the several elevation fitting models mentioned above ,with the functions of data input, compiling, analysis and data output is produced and the well performance in the above two case studies with it demonstrates the reliability and feasibility of the syetem.