Integration of terrestrial laser scanning and UAV-SFM technique to generate a detailed 3D textured model of a heritage building

The digital twin is among the Top 10 of the strategic technological trends for the period 2007-2019, and it represents a powerful tool for the conservation and enhancement of cultural heritage. It reproduces with "precision" a physical asset, thus allowing to investigate its structure and to analyze the deformations that occur over the years. Various techniques have been introduced to obtain high-resolution 3D models. Among these, the Terrestrial Laser Scanner (TLS) is widely recognized as the gold standard to generate accurate 3D metric reconstructions. TLS allows acquiring a lot of data (point cloud) in a fast way, being not in physical contact with the objects of investigation. By integrating the point cloud coming from the TLS with the one coming from the photogrammetric processes based on the Structure from Motion (SfM) and Multi View Stereo (MVS) techniques, it is possible to obtain a complete model of the object under investigation. The Unmanned Aerial Vehicles (UAV) photogrammetric technique allows to investigate possible elements not detectable by TLS. Both techniques, if well performed, can show comparable accuracies. Data fusion approach, based on multi-sensor and multi-scale integration, was proposed in the present work as the optimal solution to exploit the potential of the various techniques. A high-quality virtual twin from the All Saints' Monastery of Cuti (Puglia) was produced. The resulting detailed 3D textured model was generated by integrating digital photogrammetry with laser scanning data. A discussion on data acquisition procedures, modeling approaches and accuracy of results is provided.