3D cave mapping with handheld and terrestrial laser scanning
Author: Tommaso Santagata
In northern Italy, in the pre-Apennine area of Reggio Emilia is the "Tana della Mussina," a cave famous for archaeological artefacts found in excavations made in 1872 by Gaetano Chierici. As part of a research project with a local caving group - the GSPGC - the virtual Geographic agency Vigea recently 3D scanned the entrance part of this cave system using the Leica BLK2GO, a handheld imaging laser scanner.
Mobile scanning allowed a team led by Tommaso Santagata from Vigea to map more of the cave than in previous surveys, thanks to the equipment’s smaller size, lighter weight and fast scanning speeds. This technique has the potential to allow cave researchers to capture 3D detail in challenging sites.
3D mapping the Tana della Mussina
The project was organised by the GSPGC caving group and the FSRER caving association. Since 1967 the GSPGC has carried out exploration, research and study of the underground world in Italy and internationally. The group has discovered and explored numerous caves, often of considerable development and depth. They take part in many exploratory and research collaborations with most Italian speleological (cave study) groups, both regionally and nationally.
The Tana della Mussina is part of the Cà Speranza-Mussina cave system, which itself is part of the Messinian gypsum (dated between 5.6 and 6 million years old). The gypsum developed with a series of discontinuous chalky outcrops characterised by the presence of several sinkholes, in many cases occluded by landslides of clay and marl, which drain the surface waters feeding karst systems. Karst is an area of land formed of soluble rocks such as limestone, dolomite, and gypsum. Gaetano Chierici’s excavation of the cave in 1872 found human remains from the Aeneolithic period (third millennium BC) and ceramic, flint and copper artefacts.
Terrestrial Laser Scanning vs mobile mapping in cave systems
Terrestrial Laser Scanning (TLS) instruments are increasingly used to 3D map natural and artificial caves for study, providing a high level of accurate detail. However, it’s not always possible to create a complete map. Underground environments are challenging by nature, can be difficult to access through narrow and low passages, may contain high water levels and its cold temperatures make studies difficult.
“There are sometimes limitations in the use of laser scanners which require tripods, or to be held in difficult positions to work safely, compromising the possibility of 3D scanning some complete cave environments. Handheld imaging laser scanners are newer instruments able to provide a 3D point cloud of the environment while walking. This kind of technology can be used for the almost complete capture of cave systems thanks to the possibility of moving much more comfortably and detecting in faster times,” Santagata explains.
Testing the BLK2GO handheld imaging scanner in Tana della Mussina
As part of the GSPGC and FSRER project, Tana della Mussina was the object of 3D scanned surveys in 2019 and 2020. In the first survey, the cave was 3D scanned using a Leica ScanStation P40 survey-grade, high-definition 3D laser scanning solution and the BLK2GO, a handheld, wireless, and lightweight imaging laser scanner. The data acquired was processed to create topographic maps. In June 2020, the BLK2GO scanner was tested with the objective to 3D scan the same part of the cave already mapped in the previous campaign.
Santagata explains the mapping process, “Integrated with an Inertial Measurement Unit (IMU), the BLK2GO allowed us to 3D map and acquire RGB data information to obtain coloured 3D point clouds. The BLK2GO recreates spaces in 3D as you move. Paired with an iPhone and using Leica Geosystems’ dedicated application, it allowed us to view a preview of the results in real time and control the instrument, with the possibility of acquiring photographs and adding GeoTags to be viewed in the exported point clouds.”
Future of cave scanning – combining instruments for freedom and high definition
Santagata reflects on the success of the project and the potential for mobile mapping in cave scenarios, “New innovations in 3D laser scanning technology can bring progress in speleology, especially through the use of portable mapping systems. Handheld mobile mapping tools such as the BLK2GO are able to get different details from traditional laser scanner systems (which can guarantee much more precision and higher definition) allowing us to detect in 3D in underground environments with more freedom.”
And crucially, through the integration of different systems, it is possible to obtain greater detail in the areas of interest using a terrestrial laser scanner and get a rapid global mapping of the environment in a short time with handheld systems - an ideal result.”
Key people involved in the project: Tommaso Santagata (Vigea - Virtual Geographic Agency), Valerio Brunelli (Leica Geosystems Italy) and Stefano Bergianti (Gruppo Speleologico Paletnologico Gaetano Chierici di Reggio Emilia).
DE WAELE, J., FABBRI, S., SANTAGATA, T., CHIARINI, V., COLUMBU, A., PISANI, L.(2018) Geomorphological and speleogenetical observations using terrestrial laser scanning and 3D photogrammetry in a gypsum cave (Emilia Romagna, N. Italy). Geomorphology, 319, 47-61.