The GPS height conversion method based on moving-surface fitting

How to transfer GPS heights into normal heights has become a hotspot in survey engineering. There are many GIS fitting methods adopted in GPS heights conversion. A solution is sought the points where collocated by GPS (getting h) and geometry leveling (getting H) in certain area, and we could get the values of Quasi-geoid of these points. We call these points GPS/leveling points, namely the known points. In this method, we consider the Quasi-geoid in a certain area of interpolation to be a polynomial surface or other mathematical model, then we can construct the mathematical model by the plan coordinates X, Y and N of these known points, N=f(X,Y), using this model we could calculate the N of other GPS points, namely, the points of interpolation by their plan coordinates X and Y. Then, we could get the H by the formula H=h-N. Among the many fitting function models, the moving-surface model is a comprehensive model fitting. It has an overall weighted-type fitting model of discrete features, you can use in a larger area; polynomial fitting model also has the advantage of continuity, high precision interpolation function. The basic idea is to interpolate each point as the center, using a number of interpolation points around a given point corresponding to interpolation polynomial fitting of the point values, which is a special kind of local approximation method. It can easily change the local polynomial interpolation using the number of parameters to adapt to fit flat or mountainous areas, without undermining the basic structure of the model. The paper focused on a well-applied model used in GPS height conversion, the moving-surface model has the characteristics of both the continuous model and the discrete model, the general form is presented in this paper. The example shows that the model is effective and something useful is concluded.