الفهرس 
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Abstract
Positioning is one of the main goals of geodesy.In order to define the position of any point on the earth on the earth surface, it is necessary to determine its three coordinates or two coordinates referred to a 3Dor 2D coordinate system.
The geodetic network of positioning in egypt have been established at the first decades of the last century. observations for astronomic coordinates, base lines, azimuths, horizontal and vertical angles are traditionally taken.Helmert 1906 ellipsoid was adopted and linked to the geoid in egypt at the initial point O1, so the old egyptian datum was defined.
The observationns were not gravimmetricaaly reduced to the normal gravity field at that time because the geoid was not defined.Network 1 is not adjusted in one block, but in dividual sections.so, network i was not in good harmony ant not very accurate.Network 2, established later, was not reduced amd not adjusted at all. so, network 2 suffers from consistency and accurancy problems.Accordingly, the egyptian datum has some problems and it is not well defined.
Nowadays GPS plays an important role in establishing the global and national positionong networks.GPS is also used in strengthening the old traditional national networks.GPS is very precise technique with respect to the traditional techniques.Foe example, network 1 in egypt has an accurancy around 1:100.000 while the GPS network HARN, made by ESA, has an accurancy of 1:10.000.000 which is 100 times more accurate than the former one.
The traditional network of egypt is defined on Helmert 1906 which is local datum, its center dose not coincide with the center of gravity of the earth.
GPS networks are defined on the geocentric datum WGS-84.For its easiness fast, high accuracy, GPS is used very offtenly.In the same time it is very difficult to replace the old exisiting map system working about 100 years in egypt.The work is done using GPS which produces WGS-84 cooedinates and the local coordinates on ald egyptian datum OLD are required.Therefore, the transformation of coordinates between the two systems is essential purpose.