精密單點定位(Precise Point Positioning, PPP)為一種利用精密衛星星曆和衛星時錶誤差等誤差改正產品進行單點定位的定位方法，PPP無需仰賴基站的設置，使用者只需一台接收儀便可以作業。由於PPP能提供ITRF坐標框架內公分級精度的定位成果，因此被廣泛應用於科學研究以及工程應用等領域。國際上已有數個線上PPP服務，然而各服務所提供之服務項目略有不同，例如支援的衛星星系以及坐標框架等等。本研究嘗試建立一個針對台灣地區需求所設計的線上PPP服務，稱作台灣線上精密單點定位服務TOPS (Taiwan Online Precise Point Positioning Service)，其特色在於它可透過台灣區域變形模型將PPP計算成果由ITRF坐標框架轉換至TWD97[2010]坐標框架，使其除了能支援ITRF坐標框架的定位成果外，還能支援TWD97[2010]坐標框架的定位成果。為了解TOPS定位成果的可靠性，本研究分別對TOPS在ITRF坐標框架以及TWD97[2010]坐標框架下的定位成果進行精度分析。根據分析成果，TOPS在ITRF坐標框架下，其靜態模式下的每日解定位誤差的RMS值於E、N、U方向為1公分左右，而動態模式下的68%平面與高程定位誤差皆可在1小時內收斂至4公分左右。另外，TOPS在TWD97[2010]坐標框架下，其靜態模式下的每日解定位誤差的RMS值於E、N方向分別為2.2公分以及2.4公分，U方向為9.2公分。

Precise Point Positioning (PPP) is an optimal approach which provides position solutions by using error correction product. PPP does not require simultaneous observations from base stations, users can conduct field work with a single GNSS receiver. Since PPP can provide positioning results at centimeter-level precision, it is widely used in scientific research and engineering applications. Several online PPP services have been developed by different organizations (e.g., GAPS, APPS, CSRS-PPP and magicGNSS) and the performance of these online services are proved to be stable and reliable. In this research, we implement an online PPP service which is designed for the needs of Taiwan, which we call Taiwan Online Precise Point Positioning Service (TOPS). TOPS support GPS PPP and GPS/GLONASS PPP in static and kinematic mode. Moreover, with the help of Taiwan deformation model, TOPS can provide output result not only in ITRF but also in TWD97[2010]. An accuracy evaluation was also conducted to test if TOPS output results is reliable. According to the evaluation results: in static mode, daily solution can provide around 1 cm positioning accuracy (RMSE) in E, N and U directions; in kinematic mode, TOPS positioning accuracy (68% positioning error) can converge to about 4 cm in both horizontal and vertical directions within 1 hour. As for TOPS solutions in TWD97[2010], the RMSE of TOPS daily solution in static mode is 2.2 cm, 2.4 cm and 9.2 cm in E, N and U directions.

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