Abstract
The conversion of theoretical, as well as geometric heights to practical heights requires the application of geoidal undulations from a geoid model. The various global geopotential models that are readily available for application in any part of the world do not best-fit regions, as well as countries. As a result, there is a need to determine the local geoid models of local areas, regions and countries. This study determines the local geoid model of Kampala in Uganda for orthometric heights computation by comparing three plane geometric geoid surfaces. A total of 19 points were used in the study. The least squares adjustment technique was applied to compute the models’ parameters. Microsoft Excel programs were developed for the application of the models in the study area. The Root Mean Square Index was applied to compute the accuracy of the models. The three geometric geoid models were compared using their accuracy to determine which of them is most suitable for application in the study area. The comparison results show that the three models can be applied in the study area with more reliability, with greater confidence in model 2.
Highlights
Research and Development of a system of Global Navigation Satellite System (GNSS) positioning have made a method of surveying faster, easier and more accurate than before in the application of both scientific and applied geodesy and especially for geoid modelling when gravity data is unavailable
The points were observed using Trimble R7 receivers to obtain their coordinates and ellipsoidal heights. 4 of 19 of the existing/known orthometric heights of the points were obtained from the Ministry of Land, Housing and Urban
They were computed using the ellipsoidal heights from GNSS observation carried out with Leica 1200 GPS receivers and accessories and the geoid heights obtained from a global geoid model (EIGEN6C4) adopted for geodetic computation in Uganda
Summary
Research and Development of a system of Global Navigation Satellite System (GNSS) positioning have made a method of surveying faster, easier and more accurate than before in the application of both scientific and applied geodesy and especially for geoid modelling when gravity data is unavailable. The geoid according to Heiskanen and Moritz (1967) is the “mathematical figure of the earth”. It is the surface which coincides with the mean sea level assuming that the sea was free to flow under the land in small frictionless channels. The actual measurements made on the surface of the earth with certain instruments are referred to the geoid (Oduyebo et al, 2019). The geoid may be obtained by modelling from among others to serve as a vertical reference, as well as a datum for height determination. A global geoid is designed as global bestfit for the whole world with each country adopting her own local or regional version to fit her own mapping needs and purposes, as well as serve as a datum in engineering specifications
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