Cloud-to-cloud assessment of UAV and TLS 3D reconstructions of cultural heritage monuments: the case of Torre Zozzoli

In the field of Cultural Heritage preservation and enhancement, detecting objects quickly and inexpensively, with the possibility of repeating measurements several times for monitoring any deterioration, has become an increasingly significant requirement. The existence of a conspicuous historical heritage across the Italian territory often forces local authorities to orient their survey strategies towards the research of the most economic, but still efficient, solutions. Due to these reasons, also in consideration of possible emergency situations, it is necessary to find the optimal solution to allow a timely and comprehensive detection of exhaustive 3D digital object reconstructions. An important task is therefore to test the potential accuracies of recent measurement technologies and procedures in order to produce high quality results. This study analyzes the generation of three-dimensional reconstructions of Torre Zozzoli, an historic fortified tower located 25 km from Taranto (Apulia region, Italy), through two close-range detection techniques, by comparing Terrestrial Laser Scanner (TLS) and Unmanned Aerial Vehicles (UAVs) photogrammetric imagery. To arrange and improve the methodologies of ground control point measurements, two survey techniques were implemented by means of a Total Station (TS) and a GNSS receiver in nRTK mode. Lastly, using the cloud-to-cloud (C2C) comparison tools and implementing three distributions of GCPs, UAVs and TLS points clouds were compared. Considering their accessibility in terms of costs and use, photogrammetric products from UAVs, represent a valid alternative to TLS-based 3D data in multi-temporal analysis.