As typical illustrations of the potential use of such data, we can mention:

• calibration of mobile systems, for instance SLR or GPS antennas, using simultaneous measurements of instruments referring to the same technique
• repeated measurements on a marker with mobile systems (for instance mobile SLR or VLBI), using non simultaneous measurements of instruments referring to the same technique
• changes in antenna location for GPS or DORIS
• co-locations between instruments referring to different techniques, which implies eccentricities, except in the case of successive occupancies of a given marker by various mobile systems

Usually, co-located points should belong to a single IERS site.

Extensions of the IERS network

Recently, due to the requirements of various user communities, the initial IERS network has been expanded to include new types of systems which are of potential interest. Consequently, the present types of points allowed in IERS and for which a DOMES number can be assigned are (IERS uses a one letter code for each type):

• satellite laser ranging (SLR) (L)
• lunar laser ranging (LLR) (M)
• VLBI (R)
• GPS (P)
• DORIS (D) also Doppler NNSS in the past
• optical astrometry (A) -formerly used by BIH-
• PRARE (X)
• tide gauge (T)
• meteorological sensor (W)

For instance, the cataloguing of tide gauges co-located with IERS instruments, in particular GPS or DORIS is used for the GLOSS program under the auspices of UNESCO.