GPS测定坐标转换至地方坐标

GPS测量得到的是WGS-84中的地心空间直角坐标，而工程施工中通常使用地方独立坐标系，要求得到地方平面坐标。平面转换模型原理简单，数值稳定可靠，但只能适用于小范围的GPS测量。空间转换模型可用于大范围GPS测量，分为七参数转换和三参数转换两种。鉴于北京54坐标的大地高通常不能精确已知，对这两种参数转换方法得到的平面坐标的精度进行了比较，得出大地高精度主要表现为对高程的影响，对平面坐标影响较小的结论，同时，还讨论了七参数与三参数对转换结果的影响。

Transformation from GPS determined coordinate to local system

Results of GPS positioning are usually represented in WGS-84 frame. In the applica-. tions in construction, local grid frame is usually adopted. This paper introduces two algorithms for transferring the GPS result to local grid frame,plane transfer model and the space transfer model. The plane transfer model is understandability and reliable, but it is not suitable for large area GPS network. The space transfer model can be used in large area GPS network. Space transfer model can be divided into seven-parameter and there-parameter model. Because ellipsoidal heights on Beijing-54 ellipsoid are usually not known precisely,its inference to plane coordinate precision is analyzed and we found that the precision of the plane coordinate influenced by the ellipsoidal height is very small. The difference between seven-parameter and there-parameter model also discussed.