To transfer the Inter-national Terrestrial Reference Frame to the HARN, the HARN was connected with four IGS stations. The second network was established to cover the cultivated areas (Nile Valley and Delta) so it is called the National Agricultural Cadastral Network (NACN) with spacing 30 to 40 km. The first net is called High Accu-racy Reference Network (HARN) and consisted of 30 stations, 200 km spacing. Based on this modern concept, in 1992, the Egypt Survey Authority (ESA) established two networks. Recently, a set of the coordinates established by using GPS and referred to an international terrestrial reference frame could be used as a three-dimensional geocentric reference system for a country. One of the fundamental goals of geodesy is to precisely define positions of points on the surface of the Earth, so it is necessary to estab-lish a well-defined geodetic datum for geodetic measurements and positioning computations.
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