ETRS89 to and from ITRS

The transformations between ETRS89 (European TRS 1989, the Europe-fixed version of WGS84) and the various versions of the ITRS (International Terrestrial Reference System) are published by IERS (International Earth Rotation Service) via their Internet site. The easiest way to carry out these transformations is using the ETRS89/ITRS transformation tool on the EUREF Permanent Network (EPN) website – http://www.epncb.oma.be/_productsservices/coord_trans/.

The usual application of these transformations is in dealing with GNSS coordinates determined in a ‘fiducial network’ using IGS permanent stations as fixed control points and using IGS products such as satellite ephemerides, satellite clock solutions and Earth orientation parameters. In this application, the coordinates adopted for the fixed IGS stations should be ITRS coordinates in the same realisation of ITRS as used to determine the IGS precise ephemerides and other products. The ITRF coordinates of the IGS reference stations at the epoch of observation are obtained by multiplying the ITRF station velocity by the time difference between the ITRF reference epoch and epoch of observation and adding this position update to the ITRF reference epoch station positions.

The resulting coordinates of the unknown stations are in ITRS at the epoch of observation. The EPN transformation tool referenced above can then be used to obtain coordinates in a frame of the ETRS89.