In the context of large-scaale works, it is possible to use several data sources accessible via the Internet. This is notably the case of the precise ephemerides of the international GPS Service for Geodynamics (IGS).
These data are generally available with a delay of ten days, and allow real deats to be achieved both in the determination of orbits and in that of survey points.
They are obtained thanks to the measurements carried out continuously by hundreds of receiving stations and are generaly provided in the ITRF (International Terrestrial Reference Frame) system. France actively participates in this service thanks to the Permanent Geodesic Network (RGP), which is being densified.
The second GPS -related sevice is the US Coast Guard Navigation Center This service provides multiple information on the constellation: satellite status, recent failures , description of orbit files,etc …
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