It is important to recognise the significant contribution of the “super-network” of reference stations of the IGS to geodesy, and to the GNSS community in general.
Several hundred globally distributed GPS receivers (many increasingly with GLONASS tracking capability)
operate on a continuous basis, many for over ten years,
contributing data to the IGS analysis centres and other users (Figure 1).
The satellite (CPH and PR) tracking data they have collected have been used in progressive realisations
of the ITRF– the most recent being ITRF2008