Abstract In recent years, the use of unmanned aerial vehicles (UAVs) for surveying applications, especially for photogrammetric product generation, has gained considerable interest. In addition to conventional methods, such as real-time kinematic (RTK) or post-processing kinematic (PPK) methods, the Precise Point Positioning (PPP) and its ambiguity resolution (PPP-AR) methods have been a serious alternative for the direct georeferencing of UAVs due to the ability to provide a high positioning accuracy with only a standalone GNSS receiver on a global scale. Taking the fact that no specialized software has yet been developed for the use of PPP/PPP-AR methods in UAV applications into account, this study presents an open-source software, namely PPPH-UAV, that can process the kinematic GNSS data from UAVs using PPP/PPP-AR methods. The software supports GPS, GLONASS, Galileo, and BeiDou observations to compute image projection center coordinates. The output file generated by the PPPH-UAV software can be input into the process of photogrammetric product generation. These distinctive features differentiate the software from existing ones by providing a user-friendly, easy-to-use way to process raw GNSS data from UAVs. This study also presents an experimental test which is performed to validate the PPPH-UAV software results with the CSRS-PPP online service, utilizing the PPK results as reference. The results demonstrate that positioning accuracies of 35.0 and 33.6 cm are acquired for the CSRS-PPP and PPPH-UAV results, respectively, which indicates that both solutions are comparable. The study concludes that the direct georeferencing in UAV applications can be conducted with PPP/PPP-AR solutions via the PPPH-UAV software.

Heights provided by GNSS are affected by the quality of the geoid or quasigeoid model used for the transformation of the ellipsoidal heights to the orthometric or normal heights, as well as by the data processing techniques, including Real-Time Kinematic (RTK), Real-Time Network (RTN), static relative baseline, and absolute Precise Point Positioning (PPP) solutions. We employ two geoid models for the Tatra Mountains with constant and variable density of the lithosphere. We compare heights for 113 mountain peaks and passes directly measured using GNSS, applying two geoid models and two quasigeoid models – one dedicated to the Tatra Mountains and the second that is used as a national standard for GNSS applications in Poland. We also compare the results of height determination based on static GNSS measurements and post-processing to those based on RTK, RTN, and PPP. We found that the maximum differences from using different geoid and quasigeoid models reach up to 7.5 and 11.6 cm, respectively, whereas the standard deviations from height differences based on different GNSS processing techniques are just 0.8 cm with a maximum difference of 2.4 cm. Wrong tropospheric delay handling may result in an error of 17 cm. Hence, the geoid and quasigeoid models are crucial in GNSS height determination of the mountain peaks, whereas the GNSS data processing technique plays a minor role. Therefore, quick real-time RTN solutions are fully applicable for the GNSS measurements of mountain peaks and passes, even if the height difference between the reference station and the rover exceeds 1800 m, provided that the tropospheric delay is properly corrected by extrapolation or estimation.