Practical Options for the Re-definition of the Nigerian Vertical Reference System: A Case Study of Lagos State

Abstract

Adopting a height system especially in areas with spatially-vast land mass is rather a complicated choice. The choice of either a physically or a mere geometrically meaningful height system is often a difficult decision considering the level of computational and observational rigor involved in either case. For Nigeria, there is no clear legislation as to the height system that should be used by practitioners. This uncertainty about the adopted Height system for the country has resulted in a rather dangerous situation where multiple height systems are used across the country. Three options have been presented in this study for redefining and harmonizing height-related observations in Nigeria using the low lands of Lagos state as case study. The options are to convert spirit leveled elevation differences to HelmertOrthometric Heights (HOH), convert spirit leveled elevation differences to Normal Orthometric Heights (NOH) and convert ellipsoidal heights from GNSS to HOH respectively. Statistical analysis of the suggested options indicate there is no significant difference in the results obtained by all the three options within the study area at a confidence level of 95%. However, considering the observational convenience and computational simplicity, option 3 is recommended for a redefinition of the Nigerian Vertical reference System. The study further recommends that a national height system should be specified for use by all practitioners in the production of topographic plans