GPS精密單點定位在地籍測量之應用

Application of GPS Precise Point Positioning to Cadastral Surveying

利用IGS提供或自行計算的GPS衛星的精密星曆和時鐘差，使用者利用單一台的GPS雙頻接收機的觀測數據（含非差分的虛擬距離與載波相位觀測量），在全球任意位置都可以實現即時的或後級處理的高精度定位，此一定位方法稱為精密單點定位（precise point positioning，PPP）。在精密單點定位中，一般採用雙頻無電離層組合（L）虛擬距離與載波相位觀測方程式，由於GPS衛星的精密星曆和時鐘差已知，因此，每一測站待估計的參數只剩：測站坐標（X, Y, Z）、接收機時鐘差、L載波相位的週波未定值以及天頂方向的對流層延遲等。根據國內外研究結果顯示，PPP所求的點位精度似乎可與相對定位的點位精度相比擬，然而，為了未來能將此定位方式有效應用於地籍測量，那麼與PPP點位精度有關的課題，如精密星曆的種類、GPS資料蒐集時間長短等仍需進一步研究。因此，本文將以台灣地區5個衛星追蹤站約80天的GPS資料以及台灣西部地區2個GPS測站1天的資料，探討以PPP在地籍測量應用的有關課題。 Precise point positioning (PPP), based on un-differenced dual frequency GPS carrier phase observations, is a relatively new data processing technique for high accuracy static/ kinematic GPS applications. PPP is a method that performs precise position determination using a single GPS receiver. This position technique arose from the advent of widely available precise GPS orbit and clock data products with centimeter accuracy. Combining precise satellite positions and clocks with a dual frequency GPS receiver (to remove the first order effect of the ionosphere), PPP is able to provide position solutions at centimeter to decimeter level, which is appealing to many applications such as cadastral surveying. In this paper, issues relating to the application of PPP to cadastral surveying on different cadastral regions are studied, such as the initialization time for kinematic PPP, the achieved accuracies using the varied IGS precise orbit and clock products, etc. In order to evaluate the accuracies of applying PPP to cadastral surveying, a suite of approximately 180 days data of 5 satellite tracking stations of Taiwan region, are treated as test data. The PPP algorithm and the detailed test results will be presented in this paper.