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UDC: 528.21/528.232
DOI: 10.14438/gn.2014.18
submitted: 2014-10-07, accepted: 2014-10-20, published: 2014-10-31

Estimating the influence of point heights in computing datum transformation parameters

Dejan Vasić1*

1University of Belgrade, Faculty of Civil Engineering, Serbia

Abstract. Physical heights in geodesy are expressed through the theory of potential, and their definition is based on the concept of geoid and equipotential surfaces. When defining the conceptually simpler ellipsoidal heights, only the geometric aspects of the Earth’s body are considered. In recent years it becomes relatively easy to determine the ellipsoidal heights by using modern technologies of global positioning. However, these heights are measured from the geocentric ellipsoid, while, for the determination of the ellipsoidal height related to the reference ellipsoid, it is necessary to know the geoid undulation relative to the considered ellipsoid. The results of the global navigation satellite system measurements must be transformed into the state coordinate system. This procedure is called the datum transformation. To carry out the transformation it is necessary to know the ellipsoidal heights in both systems. As these heights are often not known in the state coordinate system, they are replaced by known values of the physical heights. The datum transformation based on the indicated approximation certainly changes the values of the determined transformation parameters, as well as the values of the transformed coordinates. The intensity of these changes depends on several factors, but the change of the transformation results itself affects geodetic computations in different ways.

Keywords. ellipsoid, undulation, physical heights, ellipsoidal heights, coordinates, geodetic datum

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