GPS Control Network Surveying And Height Fitting Studing Of Chujiang And Xiejiang Basin In Dayi County

Floods offen happen in the basin of C hu Jiang and Xie Jiang in Dayi county, Chengdu city, Sichuan province, which cause a huge loss to local residengts. So Dayi county water authority decide to strengthen the governance of the channel and build water conservancy project. This measuring of E-class GPS control network is a infrastructure project, which providing datum for large scale surveying and the constructing of water conservancy facilities.In the project, taking the 5 D-class control points in measurement zone as the plane datum points of constraint adjustment, calculating the coordinates of E-class control points. Then taking 2 national 2-class leveling points in measurement zone as the datum points of height, using 4-class leveling measuring a part of control points, and then bring the result of leveling in HGO data processing software.of Hi-Target, calculating the elevation of residual control points through the method of quadric surface fitting. Because the control points of leveling measuring take a large propotion in entire network, the heights of calculating in HGO software have a high precision, can be a standard datas to compare when analyzing the precision of height fitting model.This article mainly analyzes the precision of gravity simulating doing height fitting of control points. By writing programs to calculate the height anomaly of all control points in measurement area in EGM2008 earth gravity field model, and then by using quadric surface fitting out the real relation between EGM2008 height anomaly and the real height anomaly. After completion of quadric surface fitting, getting the fitting heights of control points in entire network, then acquires the residual error by comparing with standard datas, and calculates the inside and outside precision of the model.In order to enhance the precision of height fitting further ly, needing the terrain correction on the basis of EGM2008 earth gravity field model. The main method is through the SRTM dem data to calculate the RTM height anormaly of all control points in measurement zone, and then carries on the quadric surface fitting. Through the comparison and analysis, finding that the accuracy of height fitting which is compared with previous methods has a certain degree of increase after terrain correction, it completely can achieve the height's precision requirement of lower level's control points in mountainous place, and this method can be applied in the similar engineering project.