Integrated Geomatic Techniques for Georeferencing and Reconstructing the Position of Underground Archaeological Sites: The Case Study of the Augustus Sundial (Rome)

Abstract

A large part of the archaeological remains still to be discovered and excavated are not in remote and depopulated areas of the earth but are often beneath urban centres that have buried them with centuries of debris and later constructions. Excavating in these contexts is much more complex than digging in rural or sparsely inhabited areas because of the constraints imposed by existing buildings and infrastructure. It should also be considered that within an urbanised area, any archaeological remains are concentrated in the subsoil of the historic centre, which is, therefore, often surmounted by buildings that are more recent than the remains but historical as well, and thus, of considerable value and vulnerability. For this reason, an archaeological excavation in an urban area must be preceded by a real feasibility study, where the potential risks for the structures above are minimised and accurately quantified. In many situations, as in the case under study, the discovery of a small segment of a structure is the only clue to reconstruct the development of the remaining part still to be excavated, which may stretch tens or hundreds of metres away from the measurable part. As a consequence, an error of a few centimetres in the survey of the excavated part can lead to errors of metres in estimating the positions of the far parts still to be excavated, and this, in many cases, as in the one under study, must absolutely be avoided. In practice, high-precision geomatic surveys, in support of the archaeological and historical interpretation of the observable structures, will help to establish the exact locations to possibly continue the excavations, helping the accurate planning of the excavation itself. Here, we have shown how the various techniques, compared to each other, have made it possible to reconstruct the location of a short stretch (less than 7 m) of the Emperor Augustus’ Sundial, the only currently visible evidence of a scientific instrument of imposing dimensions (tens of metres in length and height) that served to define some of the characteristics of the calendar that we still use today. The portion of the sundial currently observable, according to the most reliable hypotheses, is located approximately at one end of a structure and extends for several tens of metres. The accurate positioning of the observable parts in a geodetic reference system will enable to identify with certainty the possible areas in which excavation may continue and will also allow to accurately reconstruct the principle of operation of the sundial through an approach that could be defined as “reverse engineering” of the scientific instrument itself. The aim of this work is to study and thus define the combination and integration of existing geomatic techniques for this specific field of application.

Solutions and limitations of the geomatic survey of an archaeological site in hard to access areas with a latest generation smartphone: the example of the Intihuatana stone in Machu Picchu (Peru)

“…The geometry and sequence of the images to be acquired for correct photogrammetric reconstruction using smartphones is the subject of lively debate in the scientific community, which has also developed useful guidelines [19]. For this experiment, the authors have decided to proceed according to their experience gained in previous experiments [1], [2], [10] and therefore to use mainly the intermediate focal length with a single horizontal strip, maintaining an overlap between one frame and the next never minor than 60 % in the longitudinal direction.…”

“…The geomatic survey of archaeological remains is always a difficult task due to the complex accessibility of sites whether they are located in urban or more remote areas. In fact, remains in densely populated areas have problems of accessibility because they are often located in underground areas with limited space [1]. On the other hand, remains in sparsely populated areas are often remote and difficult to reach with bulky equipment [2]- [6].…”

Intensive archaeological survey at Piscina Torta: use of a low-cost RTK portable kit to materialise a UTM grid on the ground

“…Before the archaeological excavation, we decided to collect all the surface artefacts in a grid of 5x5 m. The aims were both to confirm (or modify) the chronology of the site and to obtain data that could guide us in the placement of the subsequent excavation soundings through the study of surface ceramic density. The advantages of reporting absolute geographic positions of archaeological surveys have already been debated and shown in the literature, particularly in the case of underground areas and in urban areas [8][9][10][11][12][13][14][15][16] here we propose a methodology to trace and materialise the grid for archaeological sites outdoors in open areas.…”

Roman Aqueduct Flow Estimation Using Geomatic Measurement

“…Rarer is the survey for reverse engineering, i.e., to reconstruct the functioning of an instrument [8] or an infrastructure as in the case of this study.…”

“…On the other hand, in the case in which the survey of archaeological sites needs reverse engineering, it is necessary to reconstruct the three-dimensional coordinates of a number of points generally much lower than in the previous case, but with even greater three-dimensional accuracy [8].…”