Use of Similarity Transformations to Improve GPS Heighting

M.N. J.P. Vella
Centre for Geodetic and Geodynamic Studies (CGGS)
Faculty of Geoinformation Science and Engineering
University of Technology Malaysia
Johor, Malaysia


Abstract
Corrector surfaces have been used to model the differences between the geoid and the mean sea level derived orthometric heights, which are not coincident due to varying factors. In this case corrector surfaces are derived for 25 points co-located with GPS ellipsoidal heights, orthometric heights and geoid derived gravimetric heights, which lie throughout Johor, the southern State of Peninsular Malaysia. In order to model and minimise the differences a similarity transformation is utilised for fitting the gravimetric co-geoid undulations with GPS/Levelling data. Before the transformation the comparison between GPS and levelling is a standard deviation of ± 0.151 m and a mean of 0.699 m. When tested the internal relative accuracy suggests a standard deviation of ± 0.072 m and a mean of 0.003 m, which indicates the bias between the two datum’s has been eliminated. With the valid transformation it is now possible for the GIS field user to apply accurate corrected geoid heights to GPS derived ellipsoidal heights in a rapid feature driven field mode.