In Egypt, like in many countries, there is uncertainty problem in transforming the results
of GPS into local coordinates. Escaping from that, some GPS users utilize the local
coordinates of the base station directly to produce the local coordinates of the rover
stations. In this research, this concept is applied using real observations at different
locations in Egypt. The observations are processed rigorously and the WGS84
coordinates are rigorously transformed into local coordinates. GPS observations are
processed once more using local coordinates at the base stations and the local
coordinates of the rover stations are directly obtained. The outputs from the two cases
are compared. The results are tabulated and graphically represented. A linear trend
model is established to estimate the shift in latitude, longitude and height depending on
the length and azimuth of the base line. The after all word is to which limit from the
base station, this concept could be used taking the precision of the results into
consideration.