An alternative technique for fitting the gravimetric geoid for Egypt

Abstract In this paper, a proposed geoid fitting technique for Egypt's physically determined geoid and GPS/leveling-derived geoid is introduced. First, any errors in the available GPS benchmarks are ruled out. The method relies on the absolute geoid difference, which is the physical geoid minus the geoid obtained through comparing GPS and levelling. The suggested geoid fitting technique uses an optimization algorithm scheme to choose the minimum number of the best-suited GPS benchmarks to be used for fitting the physical geoid. The least-squares prediction method is used to determine each GPS point's impact on the remaining GPS points. The subset of GPS points are used for external validations including the GPS point with the least impact on the other points, till an acceptable limit of the influence of the GPS points on the remaining ones. This step is repeatedly iterated, where the number of available GPS points is reduced by one each time. Also, the results of the first iteration are introduced. The proposed geoid fitting technique is compared with that using polynomial regression of different degrees. The results proved that, the proposed technique gives extremely better results.