The Contribution of UAV Photogrammetry for 3D Documentation. Accuracy evaluation using the Euro SDR Benchmark and Villa Ghia test sites

The use of low-cost UAVs (Uncrewed Aerial Vehicles) for documenting and creating 3D models of archaeological and architectural sites as well as geographical areas is becoming increasingly popular. As this technology has become more widespread, the need to test the precision of the acquired data, the accuracy of the models, and the level of detail of the final products has also become vital. The first chapters of this thesis briefly report the history, application areas, and fundamental principles of photogrammetry and UAV photogrammetry. The following sections focus on the selected case studies, drones and camera models, and post-processing methods in software. The methodological framework of this work was defined based on the data made available from the EuroSDR RPAS Benchmark. The benchmark is divided into three separate phases and the case study is represented by the Wards Hill Quarry in Northumberland, U.K. As will be better detailed, the three subsequent phases of data release are organized as raw data only, processing with GNSS (Global Navigation Satellite System) base station data, processing with GNSS base station data and GCPs (Ground Control Points). The distributed data were processed following a photogrammetric approach in two different software; accuracy was then evaluated for all the different steps and finally, 3D models, DEM (Digital Elevation Model), and orthoprojections were created. The accuracy and precision of these three models were tested with Agisoft Metashape. Afterward, the methodological approach set up with the benchmark data was used in a new survey carried out in Villa Ghia, Veneria Reale Italy. Data were recorded with the same sensors used in the Benchmark (DJI Zenmuse P1, DJI Zenmuse L1, and DJI Phantom 4 RTK camera), and different metric products (sparse cloud, dense cloud, mesh with texture, DEM, and Orthoprojections) were created using again two different software (Agisoft Metashape and Reality Capture). Finally, the accuracy of the processing and errors of the different datasets were analyzed and compared. Afterward, the open-source software CloudCompare was used to evaluate the accuracy of the generated 3D models based on Cloud-to-Cloud (C2C) distance and density analyses. This operation allowed us to assess the accuracy and level of details of the 3D models from a metrical and geometrical point of view. The final part of this work is then dedicated to a discussion of the different tested approaches, along with the achieved results to evaluate the results of UAVs photogrammetry in different operative scenarios related to the documentation of architectural built heritage, considering the pros and cons of this technique.