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For a long time,the standard measurement to solve the Height Survey is leveling.Though it is precise,it has some shortcomings,such as high labor-intensity,high cost and low efficiency,especially for the traffic engineering which locate in a large measurement area with long range and complicated terrain,In recent years,the GPS,by virtue of such advantages as all-weather service,global observation,high-precision,high-efficiency, low-cost,timely navigation and positioning services,has been widely used in various areas.However,it is regrettable that the positioning accuracy of GPS in elevation is not satisfactory.For example,as the geoid is not a regular surface,the GPS can not find a precise model to simulate it.We could only get the high-precise altitude,which is not essential for our project.It is practical and meaningful subject for us to turn the geodetic height,which we obtain from the GPS,into normal height,make the latter directly serve the mapping and get three-dimensional coordinates through the GPS observation.At present,in the plane measurement area,it is common to use the GPS conversion elevation fitting method to turn GPS height information into a suitable one to the project,for its technology is relatively mature.But when we face the large traffic engineering which goes a few dozen kilometers or even hundreds of kilometers across the mountains,it is a very concerned issue that how tO get the normal height by using quantitative GPS height information.This essay mainly introduces the concepts,mutual relationships of geodetic height、normal height and orthometrie height elevation systems,narrates related theories of the GPS height fitting and the principles of GPS standard(GPS elevation fitting).In addition,GPS elevation model,which has been divided into the function model,the statistical model,the combination model and gravity model,elaborates the fitting methods of various models, deeply analyzes the feasibility of GPS elevation fitting model,applicability of various models presenting the evaluation method and indicators of accuracy of GPS standard fitting. With the Hangzhou Bay Bridge Project and different fitting methods of GPS standard using Matlab programming language,the results have been comprehensively compared,analyzed, researched.The evaluation methods of accuracy of various fitting models have also been presented.Besides,this essay particularly describes the GPS height fitting method,in which the Earth’s gravity have always been taken into consideration.The best way to get GPS land height from the conversion of the normal height is to utilize GPS measurements and Earth’s gravity field model comprehensively in theory.But for the ordinary project department,it does not have access to Earth’s gravity field model.The author illustrates the data of one highway engineering and makes the elevation conversation with the "remove-restore" method in the essay.What’s more,he compares and analyzes those in direct fitting results and different fitting models comprehensively.At last,the accuracy of evaluation of different fitting models have been given and specific conclusions and recommendations have been made.
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