Published in: Civil Engineering Research Magazine (CERM), Al-Azhar College of Engineering, Cairo, Egypt, V. 29, No. 2, April 2007 ____________________________________________________________________________ ASSESSMENT OF A COST-EFFECTIVE GPS DATA PROCESSING ALTERNATIVE IN EGYPT UTILIZING INTERNATIONAL ON-LINE PROCESSING SERVICES Hoda F. Mohamed (1) , Sherine S. Ismail (2) , and Gomaa M. Dawod (1) (1) Survey Research Institute, National Water Research Center, E-mail: dawod_gomaa@yahoo.com (2) Nile Research Institute, National Water Research Center Building, El Qanater, Egypt, P.O. 13621, Email: sherine_shawky@yahoo.com Abstract River Nile is one of the natural rivers that are subjected to erosion and sedimentation and accordingly to the change of its bed levels and contours. These changes in bed levels may affect different river usages and characteristics such as navigation, bank stability and morphology. Nile research Institute (NRI) is performing a continuous river hydrographic and topographic survey starting from 1979 up till recent survey of the river (on going now). The recent maps are now produced by NRI in cooperation with the Egyptian Survey Authority using the most advanced techniques of Global Positioning Systems (GPS). Over the last few years, a number of free of charge on-line GPS processing services have been established and being available over the Internet. In order to judge two of these processing services; namely the PPP and AUSPOS services, static GPS observations that have been collected over 10 national GPS stations have been uploaded to both websites. The attained results show that the PPP service produces 3D standard deviations that have a mean of 0.090 m, and an accuracy average, when compared to the published coordinates, equals 0.209 m. Similarly, the accomplished outcomes of the AUSPOS service yield standard deviations with a mean of 0.026 m, and an accuracy average equals 0.240 m in the 3D space. Concerning the differences to the ESA stations’ coordinates, the comparison reveals that the PPP results are better than the AUSPOS results by approximately 13%. Investigating the on-line GPS processing services demonstrates several merits: (1) they are free of charge, (2) there is no need to purchase a processing software package, (3) those services are very useful for beginners GPS users who do not have a great experience in GPS processing strategies; and (4) using IGS stations to tie local GPS networks implies that receivers over base stations are not needed to be deployed in the field campaigns, and hence the time needed to collect data is considerably reduced. These advantages yield a substantial cost-saving in GPS surveying and mapping projects, and thus, on-line GPS processing services are recommended to be employed particularly for GPS campaigns in national development projects in Egypt. 1