Abstract: What GPS measurement gets are WGS-84 geocentric spatial rectangular coordinates while what is used in engineering construction is generally local independent coordinates. The two coordinates can be mutually transformed by Ye Xue'an principle of two elliptic balls and by plane or spatial transformation models. However, it was found in the data processing using GPS software in a control net engineering measurement that the transverse had a poor accuracy. Therefore, the results of the error compensation of 2D base line of two kinds of coordinates in GPS net were compared and analyzed. It was concluded that in setting up independent control net by using GPS, the coordinates in the data processing should be made in conformity with that densified by conventional means.

Key words: GPS, Coordinate transformation, Data processing, Traverse accuracy