------------------------------------------------------------------------- ITRS and WGS84 Last update : 2013-12-11 ------------------------------------------------------------------------- In general the ITRS (and its realizations ITRFyy) are identical to WGS84 at one meter level. Meanwhile there are two types of WGS84 realizations: - New realizations of WGS84 based on GPS data, such as WGS84(G730, G873, G1150 and G1674). These new WGS84 realizations are coincident with ITRF at about 10-centimeter level. For these realizations there are no official transformation parameters. This means that one can consider that ITRF coordinates are also expressed in WGS84 at 10 cm level. However, the most recent G1674 realization adopted ITRF2008 coordinates for more than half of the reference stations and velocities of nearby sites for the others. Thus, ITRF2008 and WGS84(G1674) are likely to agree at the centimeter level, yielding conventional 0-transformation parameters. For more information about WGS84 realizations, see: . U.S. National Imagery and Mapping Agency, "Department of Defense World Geodetic System 1984 -- Its Definition and Relationships with Local Geodetic Systems." NIMA Technical Report 8350.2 3rd release, St. Louis, MO, 23 June 2004. http://earth-info.nga.mil/GandG/publications/tr8350.2/tr8350_2.html . Wong R., C. M. Rollins and C. F. Minter (2012) Recent Updates to the WGS 84 Reference Frame, Proceedings of the 25th International Technical Meeting of the Satellite Divison of the Institution of Navigation (ION GNSS 2012), p1164-1172. - old realization based on U.S. Navy Navigation Satellite System, commonly known as DOPPLER Transit, and provided station coordinates with accuracies of about one meter. With respect to this realization we published, some years ago, transformation parameters between ITRF90 and this Doppler realized system: Parameters from ITRF90 to WGS84-Doppler realized system T1 T2 T3 D R1 R2 R3 UNITS -----> (m) (m) (m) (ppm) (") (") (") ----------------------------------------------------------------------- 0.060 -0.517 -0.223 -0.011 0.0183 -0.0003 0.0070