Efficient three dimensional survey techniques and their comparison in open software in the archaelogical test site of “ninfeo maggiore” and “ninfeo minore” of Formia (Latina Italy)

In Europe and beyond, the cultural and archaeological heritage may have considerable extensions of hundreds of square metres if not kilometres. It is then necessary to study highly efficient techniques able , at the same time, to maintain centimetric accuracy. In these contexts, the SLAM technique can be an efficient solution. We tested the latter in a survey of a portion of the so-called Roman Villa of Caposele, also known as Villa Rubino in Formia, (Italy): the "Ninfeo Maggiore"and "Ninfeo Minore"(Major and Minor nymphaeum). The two structures had to be surveyed for both conservation and study purposes and to allow a virtual visit, which is particularly important since they are located inside a private property. The structure is complex, with a succession of rooms and environments in an archaeological complex extending approximately 480 metres in an east-west direction and approximately 50 metres in a south-north direction. We decided to survey both nymphaea with the "GEOSLAM Zeb Horizon", also surveying all the internal connecting rooms and corridors between them. Both nymphaea were also surveyed with a "Faro"terrestrial laser scanning, to allow comparison. To verify the validity of the SLAM on the outside, a survey was carried out using a DJI Matrix drone with laser scanning. The comparison showed very limited deviations whose statistical validation is in progress, demonstrating that the SLAM technique can advantageously be used in such vast archaeological complexes where the efficiency and completeness of the survey is more important than the millimetric accuracy.