Abstract
DERIVATION OF ORTHOMETRIC HEIGHT FROM GNSS ELLIPSOIDAL HEIGHT USING POLYNOMIAL SURFACE FITTING
*Prof. Ismat Elhassan and Eng. Ziyad Alnajm
ABSTRACT
The importance of geoid formation arises from the fact that it is the best way to transform ellipsoidal heights derived from Global Positioning System (GPS) measurements based on the ellipsoidal surface to orthometric heights that are normally used in surveying and civil engineering applications. There are various techniques used to form geoid models. All these are based on either gravimetric or geometric modeling. In this paper, a geometric approach where a simple polynomial model using Least squares method was developed from the combination of orthometric heights of few control points determined by automatic level observations, with ellipsoidal heights of the same points, from Differential Global Positioning System (DGPS) for a limited area within King Saud University (KSU) campus, in Riyadh, Kingdom of Saudi Arabia (KSA). Statistical test and analyses of results were carried out. It has been demonstrated that orthometric heights of ±22cm accuracy can be obtained after transforming ellipsoidal heights to orthometric heights via the formed geoid model using limited control points. The results of the obtained model compare favorably with some of the existing methods tested by other authors over larger areas using greater number of control points.
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