Abstract
Abstract. The task of documentation and conservation of Cultural Heritage defines the challenges that geomatics techniques have to overtake in order to provide different solutions that combine the automation of processes with accurate results. The employment of integrated technologies allows improving the documentation of Cultural Heritage from a quantitative and qualitative point of view. The use of range and image-based techniques ensures the possibility to completely record articulated structures such as building with underground environments. The latter present often problematic survey conditions that imposed well planned and appropriate solutions. In this context, the paper presents the results of a 3D survey of the underground “Sybil hypogeum” and the related overhead church located in the Archaeological Park of Lilibeo (Marsala, Southern Italy). An integrated survey was planned in order to combine laser scanning technology with terrestrial-based and Unmanned Aerial Vehicle (UAV)-based photogrammetry to acquire the three-dimensional data of the whole complex (underground environments and overhead church). The aims of the work are related to test a topographic approach by a traverse method for scans registration and to archive a complete and detailed 3D model of the whole area. This model could be used to prevent the risk of information’s loss and to improve the knowledge of the site.
Highlights
Accurate and complete documentation of archaeological underground environments, especially if they are decorated, is a challenging task in order to promote the enjoyment of tourists, to favour the conservation of the sites and to prevent the risk of information’s loss
3D data can be used for the virtualization of archaeological underground environments, to produce virtual visits and apply virtual restoration techniques (Beraldin et al, 2002). 3D data can be captured by a terrestrial laser scanner or closerange photogrammetry
The integration of terrestrial laser scanner and close-range photogrammetry can assist in the generation of spatial and visual records of heritage sites (Davis et al, 2017)
Summary
Accurate and complete documentation of archaeological underground environments, especially if they are decorated, is a challenging task in order to promote the enjoyment of tourists (often these sites are inaccessible), to favour the conservation of the sites and to prevent the risk of information’s loss. Some problematic conditions as the high level of humidity, the low temperature and the insufficient environment lighting should be considered for the survey (Gallay et al, 2015) Another important issue in underground surveying is related to the orientation and registration of underground surveys to the surface ones; this aspect requires a careful planning phase and the use of suitable devices and appropriate working approaches. The laser scanner survey was suitable to test a topographic approach by a traverse method for scans registration This approach is very useful for the study of underground environments where the structure complexity could make cloud-to-cloud registration very difficult. The need to acquire the entire external surface of the church required the integrated use of terrestrial laser scanners and UAVs (Unmanned Aerial Vehicles) to complete the 3D documentation. Terrestrial laser scanner survey of the hypogeum and of the outer wall of the church were used to evaluate the terrestrial-based and UAV-based photogrammetry acquisitions of the same structures
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