Evaluation of the various orthometric height systems and the Nigerian scenario – A case study of Lagos State.

Abstract

Though considered the easiest in 3-Dimensional Point Positioning, the choice of a heightsystem especially in areas with spatially-vast land mass is rather a complicated choice. Orthometricheights are naturally and fully referenced to the actual earth gravity field but laborious to computeconsidering the required approximations of gravity variation along the plumb-line from the surfaceto the geoid. Normal heights on the other hand are less laborious to compute and do notrequire actual gravity observations. Unfortunately, natural height systems are the only systems thatcan efficiently predict fluid flows. This paper has therefore examined the theory and practicalpossibility of replacing the use of Helmert Orthometric Heights with Normal Orthometric heightswithin Lagos State. A maximum height discrepancy of 1 mm was obtained in the comparison of bothsystems and thus their replaceability found suitable to within 3rd order geodetic accuracy