Relating the Nigerian reference frame and AFREF
Onyeka, Eugene Chukwunwike
A reference frame serves to define the position of an object in space. It is characterised by a reference ellipsoid and a set of datum parameters. Using a handful of reference ellipsoids, several reference frames can be obtained by seeking a best fit between the surfaces of the local geoid and the adopted ellipsoid. This fact, together with each countryys colonial history and quest for national security and defence, has resulted in the emergence of several reference systems in Africa. This makes planning of regional and continental geospatial projects exceptionally difficult. It also presents difficulties in the utilization of regional and global geodetic information. As a result of these, there have been calls for the adoption of a uniform African coordinate system to promote cross-border cooperation and connectivity as a precondition for the success of the creation of regional and continental infrastructures. The World Geodetic System 1984 (WGS 84) is the most widely used global reference system because it is the system in which the very widely used GPS satellite coordinates are expressed in the Navigation Message. It can therefore be adopted as a uniform coordinate system for Africa. Its centre and origin are coincident with the earthhs centre of mass. In Nigeria the reference ellipsoid currently in use is Clark 1880. The centre and origin of the reference system are not coincident with the earthhs centre of mass. Rather the origin is one of the triangulation stations located roughly at the centre of the associated triangulation network. Furthermore, the geoid, the reference surface for orthometric heights, has not been determined. There are, therefore, a number of difficulties to be surmounted before WGS 84 can be adopted by Nigeria and before existing geodetic information can be correctly tansformed to the WGS 84. These difficulties are highlighted in this paper and solutions to them proffered.
Event: 5th FIG Regional Conference for Africa : Promoting Land Administration and Good Governance
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