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 height system especially in areas with spatially-vast land mass is rather a complicated choice. Orthometric heights are naturally and fully referenced to the actual earth gravity field but laborious to compute considering the required approximations of gravity variation along the plumb-line from the surface to the geoid. Normal heights on the other hand are less laborious to compute and do not require actual gravity observations. Unfortunately, natural height systems are the only systems that can efficiently predict fluid flows. This paper has therefore examined the theory and practical possibility of replacing the use of Helmert Orthometric Heights with Normal Orthometric heights within Lagos State. A maximum height discrepancy of 1 mm was obtained in the comparison of both systems and thus their replaceability found suitable to within 3rd order geodetic accuracy.

Keywords

• Helmert Orthometric Height
• Normal height
• 3D Point Positioning
• Geoid
• Gravity observation