Determination Of Parameters For Datum Transformation Between Wgs 84 And Adindan-ethiopia

Global Positioning System (GPS) becomes preferable technology in Ethiopia as a result of itsrnnumerous advantages over classical methods of surveying. However, it provides geocentricrncoordinates of a point defined based on a global datum (WGS84) which differs significantlyrncompared to those coordinates realized with respect to a local datum. Ethiopia uses ADINDAN asrnthe recognized local datum and the Geospatial Information Institute (GII) is the only responsiblerninstitution to determine the transformation parameters between the national (modified Clarke1880)rnand global (WGS84) datums. However, the current official transformation parameters in use byrnthe GII are slightly different from the parameters determined by previous researches and adoptedrnin widely used geospatial software packages. In addition to this, the rotation and scale changesrnare totally ignored from the transformation parameters; while they are inclusive for the region ofrnSudan. The main objective of this study is to determine datum transformation parameters betweenrnWGS84 and modified Clarke1880 reference ellipsoid for the region of Ethiopia using thernconventional and conformal transformation models. Orthometric height to ellipsoidal heightrnconversion approaches are also while computing the transformation parameters. Nine co-locatedrnGround Control Points (GCPs) that are defined with reference to the two reference elliposids werernobatined from the GII and this study contributed to the realization of one new co-located GCP.rnResults of the study revealed that, the parameters estimated with orthometric height method andrniterative solutions gives better results for all models and the later approach were great. ThernMolodensky-Badekas seven parameters model with iteration solution is the most stable andrnsuitable transformation model for Ethiopia. The transformation parameters from WGS84 tornClarke1880 with inherent uncertainties are 169.674 m± 0.132 m, 14.801 m ± 0.132 m, -204.841rnm ± 0.132 m translation, -0.216 ± 0.114, 0.046 ± 0.127, 2.815 ± 0.173 rotations in the x-, y-, andrnz- components respectively and 0.288 ± 0.503 scale change. The centroid points used arern4990956.0195 m, 3807764.401 m and 1105492.297 m in x, y, and z axes respectively.

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