Determination of Parameters for Datum Transformation between WGS 84 and ADINDAN-Ethiopia

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Addis Ababa University


Global Positioning System (GPS) becomes preferable technology in Ethiopia as a result of its numerous advantages over classical methods of surveying. However, it provides geocentric coordinates of a point defined based on a global datum (WGS84) which differs significantly compared to those coordinates realized with respect to a local datum. Ethiopia uses ADINDAN as the recognized local datum and the Geospatial Information Institute (GII) is the only responsible institution to determine the transformation parameters between the national (modified Clarke1880) and global (WGS84) datums. However, the current official transformation parameters in use by the GII are slightly different from the parameters determined by previous researches and adopted in widely used geospatial software packages. In addition to this, the rotation and scale changes are totally ignored from the transformation parameters; while they are inclusive for the region of Sudan. The main objective of this study is to determine datum transformation parameters between WGS84 and modified Clarke1880 reference ellipsoid for the region of Ethiopia using the conventional and conformal transformation models. Orthometric height to ellipsoidal height conversion approaches are also while computing the transformation parameters. Nine co-located Ground Control Points (GCPs) that are defined with reference to the two reference elliposids were obatined from the GII and this study contributed to the realization of one new co-located GCP. Results of the study revealed that, the parameters estimated with orthometric height method and iterative solutions gives better results for all models and the later approach were great. The Molodensky-Badekas seven parameters model with iteration solution is the most stable and suitable transformation model for Ethiopia. The transformation parameters from WGS84 to Clarke1880 with inherent uncertainties are 169.674 m± 0.132 m, 14.801 m ± 0.132 m, -204.841 m ± 0.132 m translation, -0.216 ± 0.114, 0.046 ± 0.127, 2.815 ± 0.173 rotations in the x-, y-, and z- components respectively and 0.288 ± 0.503 scale change. The centroid points used are 4990956.0195 m, 3807764.401 m and 1105492.297 m in x, y, and z axes respectively.



Transformation Models, Parameters, Orthometric height, WGS-84, ADINDAN Ethiopia