Combination of nadiral and oblique UAV photogrammetry and HBIM for the virtual reconstruction of cultural heritage. Case study of Cortijo del Fraile in Nijar, Almeria (Spain)

Historic Building Information Modelling (HBIM) is the most effective method of rebuilding virtual 3D models of heritage buildings, and constitutes a new information management system in the field of cultural heritage interventions. In this study, photogrammetry based on Unmanned Aerial Vehicles (UAV photogrammetry) was applied as an alternative to Terrestrial Laser Scanning (TLS) for the development of HBIM for historical buildings in a ruinous state, analysing as a case study the Cortijo del Fraile, in Nijar, Almeria (Spain). Based on the analysis of the historical information of the building, a photogrammetric survey was carried out with UAV by means of a combination of nadiral and oblique photographs. In this way, a precise characterization of the object was obtained, avoiding the grey areas that are characteristic of TLS. The generated 3D point cloud served as the basis for the virtual reconstruction of an HBIM model focused on both the exterior and interior. In order to ensure reasonable agreement between the parametric model and the ground truth, a validation procedure has been established that restricts the deviations between the two. Finally, a texturizing process is applied to the HBIM model to achieve a photorealistic finish for purposes of visualization, archiving, and recording.