A Comparative Analysis of Camera Rig Parameters in Photogrammetric Software for Small-Format Oblique Camera System on Unmanned Aerial Vehicle

Utilizing small-format oblique camera systems to capture simultaneous nadir and oblique photographs from unmanned aerial vehicles (UAVs) is a common practice in modern photogrammetry. Oblique photographs provide enhanced geometric insights into building side views, terrain morphology, and vegetation, thereby enriching interpretation and classification. However, the design of camera rig parameters and their precise mathematical modeling for small-format oblique camera systems in multi-view processing is essential to ensure accurate representation of the physical camera geometry and results. This study investigates the camera rig parameters of the '3DM-V3' small-format oblique camera system, focusing specifically on the relative relationship between nadir and oblique cameras, within two prominent photogrammetric software: PIX4Dmapper and Agisoft Metashape. The research concludes that optimal parameterization involves fully constrained relative translation parameters (TX, TY, TZ)rel for the four oblique cameras, while setting approximate initial estimates as free constrained for relative rotation parameters (RX, RY, RZ)rel. This approach aligns with the physical geometry of the camera system and yields a precise camera model, as confirmed through bundle block adjustment (BBA) computations. PIX4Dmapper yields horizontal and vertical root mean square errors (RMSE) of 0.023 m and 0.019 m, respectively, while Agisoft Metashape results in RMSE of 0.018 m and 0.046 m. These RMSE values, considering the ground sample distance and ground control point accuracy, reflect the robustness of the approach. The insights from this research offer valuable guidance for industries, facilitating informed decisions regarding the selection of appropriate software and parameters for small-format oblique camera systems mounted on UAVs, thus ensuring consistency between theoretical models and real-world applications.