KEYWORDS: 3D modeling, Laser scanners, Data modeling, Cultural heritage, Data acquisition, Clouds, Unmanned aerial vehicles, Gold, 3D imaging standards, Atomic force microscopy
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.
Timely and accurate maps of land cover changes are crucial for understanding the evolution of Earth's features and, consequently, the relationships between individual and collective needs. Therefore, this information is extremely important to develop future planning strategies and tackle environmental issues. This paper aims to exploit the use of Google Earth Engine (GEE) platform to examine land cover changes over a period of about fiftheen years in the pilot site of Siponto, an historical municipality in Puglia, Southern Italy. Six atmospherically corrected Landsat data, two for each selected mission (5, 7 and 8), were collected: the former was acquired in fall and the latter in spring. Land cover information was automatically extracted from each image through the implementation of an innovative Landsat Images Classifications algorithm (LICA) based on spectral indices analysis. Six classes (water, built-up, mining areas, bare soil, dense and sparse vegetation) were detected from each image, with an average overall accuracy higher than 85%. Land cover changes were assessed comparing classification maps of the same season, showing bare soil areas as the most altered ones, having been converted into arable lands in consideration of the adavantageous geomorphological features of the investigated site. This is also confirmed by the historical events experienced by the area.
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.
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