基准约束对GPS网平差结果的影响

Influence of Datum Constraints on the GPS Network Adjustment

大尺度、高精度GPS定位中，如何引入基准信息，以及不同的基准信息对参数估计结果的影响是值得探讨的问题。本文利用GAMIT／GLOBK软件，分别采用强约束法和相似变换法对“中国大陆构造环境监测网络”基准站的GNSS观测数据进行处理，按照三种方案进行平差计算获得基准站在ITRF2008框架下的坐标。三种方案分别是：一、强约束IGS核心站水平方向0．1cm，垂直方向0．2cm；二、强约束IGS核心站水平方向1cm，垂直方向2cm；三、松约束IGS核心站水平方向和垂直方向都为10m，用GLOBK软件中的glorg模块进行平差计算。通过比较三种方案的结果得出：使用强约束法时对起算数据的约束不同会造成定位结果的差异，不恰当的约束容易引起网的形变和扭曲。而相似变换法可以避免不恰当的约束引起的网的变形和扭曲，且可靠性更高。

The problem how to select the datum constraints and evaluate their different influences on parameter estimation results in the large- scale and high- precision GPS positioning is worth discussing. In this paper, strong constraint method and similarity transformation method are used in processing the GNSS data of base stations of the Chinese Continental Tectonic Envi- ronment Monitoring Network with the GAMIT/GLOBK software. Coordinates of base stations in the ITRF2008 are obtained through adjustment calculation adopting three schemes. Scheme A： the horizontal and vertical directions are constrainted with 0. lcm and 0.2cm. Scheme B ： the horizontal and vertical direction are constrained with lcm and 2cm. Scheme C ： the horizontal and vertical directions are loosely constrained both with 10meters, and making glorg. The comparision result of the three schemes shows that, different constraints on the original data will result in different positioning precision and inappropriate constraint may lead to network deformation and distortion. In contrast, the similarity transformation method is more reliable and can avoid above - mentioned problems.