Investigation into Various Factors Influencing the Achievable Accuracy of Kinematic GNSS Height Observations for Road Surveys


Engineering Surveying; LIDAR

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Muhammed Shaakir Deal, Chief Directorate: National Geo-spatial Information, South africa,
Dr Mahmoud Abd El-Gelil, University of Cape Town, South Africa,


In South Africa, road maintenance and construction are the responsibility of the South African National Roads Agency Limited (SANRAL), which only accepts tenders for topographical road surveys carried out by conventional methods, in accordance with the Technical Methods for highways (TMH 11) guidelines. The aim of this paper is to investigate the height accuracies achievable under various conditions for GNSS observations and whether these can be used for topographical road surveys. To investigate the achievable accuracy of GNSS height observations, a 1km test bed consisting of 500 precisely leveled points was established along a road, which served the basis for all fieldwork.

Each point was occupied for more than 10 epochs, observing GPS+GLONASS satellites at a 0° elevation cut-off angle in Real Time and Post Processing Kinematic mode. The above mentioned observations allowed for the analysis of the effect of GPS-only and GPS+GLONASS observations on height accuracy. It further made provision to investigate the effect of the number of epochs per point observation. Both GPS-only and GPS+GLONASS results illustrate an achieved RMS of 14mm with more than 90% of its observations within 25mm accuracy among all observation sessions for GPS and GPS+GLONASS.

To acquire the best possible results using GNSS, the base station should be set up close to the test site, within 1 km of the road been surveyed unless provision is made for geoid modeling. GNSS height observations can provide an accuracy level that is similar to heights established by conventional methods such as total station, which are in accordance with TMH 11 specifications.

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