Determination of the coordinates of image centers in UAV photogrammetry based on PPP

Nowadays, UAV photogrammetry has been applied in wide range of applications, due to its ability in high quality data acquisition in short time and achieving high accuracy in 3D modelling. In recent years, Global Navigation Satellite Systems (GNSS) has been considered in UAV photogrammetry for the purpose of perspective center determination. They can generate the production of photogrammetry with higher quality and also reduce number of ground control points. Although, relative positioning methods have been successfully applied in UAV photogrammetry, requiring the base station is the main challenge of them. In this study, the efficiency of Precise Point Positioning (PPP) has been evaluated in perspective center determination. It can eliminate the base station and be as accurate as relative methods by formulating errors. For this purpose, UAV dataset with kinematic GNSS receiver observation from Qatour city in West Azarbaijan is used. In the proposed method, perspective centers are determined based on online processing service NRCan and aerial triangulation performed by determined positions. In order to compare the obtained results with standard method, the process is also performed based on post-processed kinematics (PPK) and REDtoolbox software. The obtained results show that UAV photogrammetry based on PPP achieves high accuracy if UAV receiver observation, image acquisition time, the distance between perspective center and phase center of antenna and global coordinate systems transformation parameters are available. Comparison of PPK and PPP shows mean difference of 2 and 7 centimeters which proves the ability of PPP method. Moreover, the coordinates of control and check points are computed based on PPP and PPK. The accuracy of PPP is 10.6 and 12.3 and PPK is 10.5 and 11.6 centimeter. Consequently, numerical analysis proves that PPP can be appropriate alternative for PPK and RTK in UAV photogrammetry with preserving accuracy and quality and removing base reference.