Known worldwide and welcoming about 3.5 million visitors each year, the Mont Saint-Michel abbey is a major centre of attraction. As it is exposed to bad weather, it benefits from frequent restoration work. The French Centre for National Monuments (CMN) is currently focusing its efforts on the Merveille building, located just to the north of the abbey’s church, and containing the cloister, refectory, work room and chaplaincy. Together, these structures make up two sets of three-storey buildings, resting on the slope of the rock and extending approximately 90 m in length, 40 m in width and up to 50 m high.
“To prepare for this restoration the CMN asked us to produce a detailed digital rendering of the site so they would have access to a very precise survey, which was not available from the existing plans they had access to,” explained Lazare Grenier, Topography and Survey Engineer at Art Graphique & Patrimoine (AGP). The company, with long experience in using FARO equipment, decided to use scanners for this application. The topography of the site is complex and they needed to work outside of visiting hours. Simply put, a maximum of efficiency was required in a minimum of time. In these conditions, AGP was able to get the most out of the methodology they use in this type of application. This consists in defining all the locations where scanners will be placed in advance of placement to limit the amount of overlapping, and above all to avoid forgetting a hidden area. “This task led us to select almost 700 locations for placing the scanners.”
For the Mont Saint-Michel site, AGP used the FARO Focus 3D X 330 over a period of four weeks in late 2014. Certain parts of the site, notably the exterior walls above the cliff, were not visible from any position on the surface, so the digitisation was done using airborne equipment: to achieve this, AGP relied on traditional photogrammetry, since the onboard scanners did not have a high enough precision. The assembly of the scans is done using SCENE software from FARO.
With many years of experience under his belt using FARO scanners, Lazare Grenier takes stock of lighter and more compact than their predecessors. They are more precise, easier to use and work off batteries. They also have increased their depth of field and are able to record scenes which are much closer, as well as much further away. These scanners also allow for digitising buildings in complete darkness or in full sunlight ensuring total safety for the public in terms of their eyesight. All of this is particularly important in an application such as that of Mont Saint- Michel, where there are many constraints for scanner placement, requiring the scanner to be placed very close to the target in some cases, and farther away in other cases.”