ETRS89 - European Terrestrial Reference System 1989 Working Committee of the Surveying Authorities of the States of the Federal Republic of Germany http://www.adv-online.de/produkte/etrs89.htm |
The ETRS89 is derived from the IERS Terrestrial Reference Frame (ITRF) global Reference System. IERS stands for ‘International Earth Rotation Service’.
The ITRF origin is at the Earth center of gravity; the Z-axis is Earth median rotation axis intersecting with the Earth crust at the "IERS Reference Pole". The IERS Reference Pole position is within the accepted tolerance (0.03”) from the "Conventional International Origin (CIO)". The Y-axis is at the zero-meridian (Greenwich-Meridian), verified by longitude measurements from a number of Reference Stations.
At the beginning of every year (e.g. 1989) about 180 worldwide Reference Stations receive coordinate sets with shift vectors for the ITRF geodetic Reference System.
The core of the European Reference System ETRS89 are the ITRF coordinates derived from European Reference Stations at the beginning of the year 1989. These coordinates are the definition of the ETRS89 and are not subjected to changes in the coordinates from European ITRF stations, caused, for example, by changes in continental drift rates.
In Europe the ETRS89 and the World Geodetic System 1984 (WGS84) provide matching results within one meter difference. As a result of the continental drift the difference grows per year about 2 or 3 cm. In the year 2020 e.g. the amount will be around 70 cm. The difference is recalculated dynamicaly by GeoDLL with all transformations using WGS84 coordinates. GeoDLL supports ITRS-Epochs by using WGS84 coordinates from GPS measurements. Therefore is in the list of the supported Coordinate Reference System a group classification "GPS Measurements - ITRS epochs" is available.
In ETSR89 geographic coordinates and (ellipsoidal) heights are calculated using the Geodetic Reference System 1980 (GRS80) ellipsoid.
A series of VLB (Very Long Baseline Interferometry) measurements across Europe did provide additional reference points which were included in ETRS89.
To make this established for Europe wide meshed grid suitable for practical use it was further condensed by measurement projects like EUREF-GPS on the European level and the DREF-GPS on the national level. It was even more condensed and hierarchically organized by the so-called C-Net-GPS measurement project executed on the German Federal Republic States level.
|