Application of GNSS-levelling for updating the base vertical network

Abstract This study explores the potential of GNSS-levelling to complement geometric levelling in the state levelling network, particularly outside the main lines. The Polish state levelling network plans to reduce the number of points from 40,000 to 16,000 during upcoming updates. GNSS-levelling is considered a cost-effective solution for filling gaps in the network, especially in rural areas. The experiment, commissioned by the Polish Head Office of Geodesy and Cartography, applied Polish geometric levelling accuracy criteria and tested them against GNSS-levelling. The goal was to develop a technique that an average surveying company could apply. The results showed that the initial hypothesis of GNSS-levelling’s suitability was not fully supported, primarily due to inconsistent vector repeatability. Accuracy could be improved by increasing the number of observation sessions or using specialized GNSS software while still maintaining cost-effectiveness. The experiment was conducted in an area where the state quasi-geoid model fits the levelling network with an accuracy of ±1 cm. Furthermore, the single vector solution (SVS) outperformed the each-to-each vector strategy (NET) in aligning with this network. Although challenges remain, GNSS-levelling demonstrates the potential and after refinement of techniques requirements, it is possible to obtain the main goal.