Introduction of the Iranian geodetic datum
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Published November, 2019

Introduction of the Iranian geodetic datum

One of the most important duties of the National Cartographic Center (NCC) of Iran as a policy-maker for preparing maps and spatial information is to provide the National Coordinate Reference Framework with a view to coordinating mapping activities and maintaining their integrity throughout the country. Therefore, after establishing the classic geodetic networks, by purchasing the first GPS receivers in 1987, NCC began to design a 1st order satellite geodetic network over Iran, and in 1991 the station coordinates of this network were released to users in the original (or Doppler) version of theWGS84 coordinate system .

Then, with the preparation of dual-frequency positioning receivers, 10 stations of the 1st order satellite geodetic network as zero-order satellite geodetic stations were re-measured in 1994 and the coordinates of these points were computed in the International Terrestrial Reference Frame 1992 (ITRF92). After that, the coordinates of 1st order satellite geodetic network as a national coordinate reference framework were presented to the relevant users in the original WGS84 coordinate system by applying the unified adjustment and transformation parameters.

After the painful Bam earthquake in 2003, the need for Iranian Permanent Geodynamic Network (IPGN) was proposed by NCC for the first time in the country to monitor the movements of the earth's crust, and the first phase of the network included 106 stations was completed in early December 2006. A report on how data was processed along with the coordinates of the points in the International Terrestrial Reference Frame 2000 (ITRF2000) was presented. Subsequently, by expanding the permanent geodynamic and GNSS network in Iran, in 2010, the coordinates of 121 IPGN stations were calculated in the ITRF2005 reference fame and were transformed in the original WGS84 coordinate system by applying the transformation parameters, which it is known as the Iranian Geodetic Datum (IRGD2010).

In recent years, by collecting continuous data and increasing the number of ground control stations, updated versions of the ITRF (related to the scientific processing software) and subsequent updates of the WGS84 coordinate system (related to the GPS measurements) are being prepared and, the WGS84 has more adaptation With the ITRF, so far, the difference between the latest version of ITRF (ITRF2014) and the recent version of the WGS84 (G1762) is currently around 1cm. However, changes in station coordinates over the past years, due to tectonic movements of the crust, earthquakes, subsidence phenomenon and other factors, continuous monitoring of these movements is one of the main requirements of maintaining and controlling the fundamental networks of the country. In this regard, based on new calculation in 2017, the report on the results of the data processing of 127 stations in ITRF2014 reference frame was presented and the new Iranian geodetic datum called IRGD2017 was introduced, which is more consistent with the coordinates of the points in the recent version of the ITRF and WGS84 (G1762) coordinate system at the reference epoch of January 1, 2017. Of course, according to the needs of the users and the preparation of existing coverage maps of the country based on the old geodetic datum, it was reviewed as IRGD2010_R1 and the station coordinates contained in the identification form were also updated.