GEOMATICS FOR THE 3D SURVEYING AND MAPPING OF CONFINED SPACES: A CASE STUDY IN BOLOGNA (ITALY)

This paper describes the experience of the 3D mapping of the Ravone torrent, which flows in the city of Bologna (Italy) for about 10 km, alternating above ground and underground segments. The work was commissioned by the Agency for the Territorial Safety and the Civil Protection of Emilia-Romagna Region, and the activities were performed by Forlì Ambiente Cooperative Company in collaboration with the DICAM Geomatics group of the University of Bologna and the UAS national training Centre of the Italian Red Cross in Bologna. The aim of the work was the complete and reliable documentation and mapping of the torrent course, fundamental for the planning and execution of maintenance operations and basis for the project of the urban redevelopment in the areas surrounding the above ground segments. The case study presents peculiar morphological characteristics that make its survey a challenging task: an elongated and repetitive geometry, a small transversal section and long underground portions. The geometric documentation required the use of different geomatic techniques performed in integration, with the aim to obtain the accurate 3D model of the whole torrent course: Terrestrial Laser Scanning, GNSS, photogrammetry by drones, classic topography by Total Station, high precision differential trigonometric levelling. In the paper all the surveying and processing phases will be accurately described, underlying all the solutions developed to face the problems related to the peculiarities of this object, and presenting the obtained final products.