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 establish a well-defined geodetic datum for geodetic measurements and positioning computations. 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. Based on this modern concept, in 1992, the Egypt Survey Authority (ESA) established two networks. The first net is called High Accuracy Reference Network (HARN) and consisted of 30 stations, 200 km spacing. 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. To transfer the International Terrestrial Reference Frame to the HARN, the HARN was connected with four IGS stations. The processing results were 1:10,000,000 (Order A) for HARN and 1:1,000,000 (Order B) for NACN relative network accuracy standard between stations defined in ITRF1994 Epoch 1996.
To evaluate the HARN & NACN, a co-joint team from NRIAG and Mansura University observed the available HARN & NACN stations in the Nile Delta. The Processing of the tested part was done by CSRS-PPP Service based on utilizing Precise Point Positioning “PPP” and Trimble Business Center “TBC”. The study shows the feasibility of Precise Point Positioning in updating the absolute positioning of the HARN network and its role in updating the reference frame (ITRF). The study also confirmed the necessity of the absent role of datum maintenance of Egypt networks. |
