Regional Quasi-geoid Refinement In Measurement

The main purpose to determine the high-precision regional quasi-geoid is to utilize GPSto instead of trigonometric leveling and direct leveling, it can take full advantage of GPSmeasurement and reduce the surveying workload. Accordingly, the cost of production can alsobe reduced. At present, the great quantity of gravity data, high-precision GPS/leveling dataand digital terrain model is used in the high-precision regional quasi-geoid. Within theindustry, the data processing and computing is too complex to afford for the institution withordinary technical and economical strength, moreover many areas lack of ground gravity dataas well as high-precision and high-resolution digital terrain model. Therefore, the applicationof this method is limited by a certain extent. Meanwhile, the choice of fitting points is still aproblem in the domestic quasi-geoid refinement study.Aiming the problem mentioned above, the EGM2008earth’s gravity field model isintroduced in the thesis, and the accuracy of the model is analyzed in detail, especially theaccuracy in Mainland China. The calculation program using the remove-restore method torefined regional quasi-geoid is developed by C#language on VS2010platform. The measureddata of3massive survey areas and2banding survey areas is utilized to refined regionalquasi-geoid by comparison. The choice of fitting points is studied. And a easy-implementedmethod for the domestic quasi-geoid refinement is been summarized. The conclusion can bemade below:(1)For the massive survey areas, use EGM2008model, combined with about10GPS/leveling points, using remove-restore method, fitting quadratic surface fitting can becalculated high precision height anomaly of the survey area. The survey area is relatively flatterrain, the number of fitting points can be reduced to8, such as the survey area is complexterrain, may be appropriate to increase the number of fitting points. The specificcircumstances is depended on the measured area and terrain complexity. Choice of the fittingpoint is very important, you should try to choose the surrounding terrain without severechanges of GPS/leveling points as fitting points, fitting points should be evenly distributed inthe survey area in general.(2)For massive survey areas, the utilization of remove-restore method to refined regional quasi-geoid based on EGM2008and GPS/leveling points ispracticable, which can full fill the elevation requirements of root control points and detailpoints in1﹕2000and lower scale topographic maps mapping.(3)For banding survey areas,this method is applied to refine regional quasi-geoid with flat terrain. The calculated accuracyof height anomaly can full fill the elevation requirements of root control points and detailpoints in1﹕2000and lower scale topographic maps mapping. The complex terrain surveyareas need further discussion and analysis.