Entering the 21st century, the application of Global Positioning System (GPS) in various aspects will be strengthened and developed. This article focuses on the latest development of GPS towards the 21st century, especially the product content, applications, and services of the current international GPS service (1GS). 1、 The development of GPS continuous operation station network and integrated service system is based on the global ground-based GPS continuous operation stations (about 200), forming the IGS (International GPS Service), which is an example of GPS continuous operation station network and integrated service system. It provides various GPS information to global users free of charge, such as GPS precise ephemeris, fast ephemeris, predicted ephemeris, IGS station coordinates and their motion rates, phase and pseudorange data of GPS signals received by IGS stations, and Earth rotation rate. This information supports numerous scientific projects in geodesy and geodynamics, including ionosphere, meteorology, reference frames, precise time transfer, high-resolution estimation of Earth's rotation rate and its changes, and crustal movement.

　　(1) IGS currently provides three types of orbits: first, the final (precision) orbit, which needs to be obtained after 10-12 days and is commonly used for precision positioning; The second is to report the orbit quickly, which should be obtained after 1 day. It is commonly used for calculating atmospheric water vapor content, ionosphere, etc; Another type is the predicted orbit. Currently, only two IGS analysis centers provide estimates of GPS clock bias. IGS currently uses nearly 70 external frequency standards among its nearly 200 permanently continuous global tracking stations, of which approximately 30 use hydrogen clocks, approximately 20 use cesium atomic clocks, approximately 20 use rubidium atomic clocks, and the rest use crystal oscillators inside GPS.

　　(2) IGS also provides information on pole shift and world time. The final daily polar coordinates (x, y) published by IGS have an accuracy of ± 0.1mas, while the corresponding accuracy of the quick report is ± 0.2mas. As a space geodetic technology, GPS itself does not have the function of measuring Universal Time (UT). However, due to the correlation between GPS satellite orbit parameters and UT, as well as the determination of Earth's rotation rate, which is the time derivative of UT, IGS can still provide daily length of day (LOD) values. IGS can now further determine the nutation term and high-resolution pole shift (up to once every 2 hours, instead of once a day). The latter is mainly due to the improvement of observation quality at IGS observation stations, rapid and timely data transmission, and improvements in data processing methods, without any fundamental changes. However, the former is a technological leap forward.

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