Determination of Parameters for Datum Transformation between WGS 84 and ADINDAN-Ethiopia
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Date
2019-12
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Addis Ababa University
Abstract
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.
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Keywords
Transformation Models, Parameters, Orthometric height, WGS-84, ADINDAN Ethiopia