A digital ecosystem for the knowledge, conservation and valorization of the medieval archaeological site of Satrianum (Tito, PZ) FOSS instruments

Giorgia Dato
Eugenio Saccà
Alessandro Spadaro

The case study concerns the fortified mediaeval site of Satrianum in Basilicata. Topographical, archaeological and architectural analysis permitted the creation of a spatial database with QGIS: further developments involve the survey of the site and the elaboration of 3D digital models to be georeferenced in the space. The complete data set obtained for the knowledge of the site allows to design projects for conservation, valorisation and usage of the site itself at several levels

Introduction

The Satriaunumarchaeological project is under the scientific direction of Francesca Sogliani and SABAP-MIC. A particular mention goes to Simona Di Gregorio, who has allowed this work to be carried out.

The study of the archaeological site of Satrianum, on concession from SABAP - MIC, began in 2000 under the direction of Massimo Osanna, in collaboration with the Superintendence for Archaeological Heritage of the Basilicata and it is part of a multidisciplinary research project of the Postgraduate School in Archaeology of Matera. Since 2005, the investigation has focused on the mediaeval settlement under the scientific direction of Francesca Sogliani (Osanna 2011; Colangelo 2011; Osanna, Capozzoli 2012).

Satrianumis currently included in an enhancement project aimed at defining the physiognomy of the Open Museum through paths of public archaeology (Format “Festivalia. Archaeology tells itself”), digital storytelling and virtual reconstruction. It is also one of the SmartLabs included in the Basilicata Heritage Smart Lab project coordinated by the Basilicata Creative Cluster.

The area of the archaeological site of Satrianum 1 used to be a mediaeval fortified settlement. It is distributed on a hill dominating the surrounding area and is located between the present-day cities of Tito and Satriano di Lucania in Basilicata ( Fig. 1 ).

Particularly important for its strategic position along axes of territorial connection that link the Ionian, Adriatic and Tyrrhenian coasts and for the abundance of resources, the site of Satrianumhas been occupied extensively since the VIII century BC, as indicated by the important results of the archaeological investigations that were carried out. In particular, the data that emerged from archaeological excavations allowed the reconstruction of the settlement dynamics of the site during the Archaic period, from the VIII century BC to the V-IV century BC. The most important phase of growth of the pre-Lucan indigenous settlement started in the VI century BC; then, with the arrival of Lucanian people in the IV-III century BC, great transformations took place in this area (Osanna and Capozzoli 2012).

Traces of transformations during the Roman period (III-II century BC) give back the physiognomy of a much less populated area, at least until the Middle Ages when the town of Satrianumwas born. Built in the last decades of the XI century, it is a particularly strategic area, also for its topographical characteristics, which constitutes a case study of particular importance: it represents the result of a process of hierarchisation and restructuring of spaces and structures willed by the noble initiative to control territories and the ways of exploiting the countryside (Sogliani 2017).

The progressive decline of the area led to the abandonment of the settlement in the XV century.

The mediaeval settlement of Satrianum, built using local limestone found in situ, represents an exemplary case of an abandoned village that, having not been affected by post-medieval and modern renovations, has maintained its architectural features and original plans sufficiently intact (Sogliani and D’Ulizia 2008).

The internal organisation of the site consists of different architectural complexes, and it is structured in three main areas:

A summit area that was enclosed by a wall with a square tower –the seat of lay power–, and a cathedral with an adjoining episcope, –the seat of ecclesiastical power–.
a first village along the western slopes.
a second village on the southern side.

The course of the research and study led to the analysis of the state of conservation of the fortified settlement of Satrianum, and the design of a feasibility project for its restoration through the programming of a dedicated digital archiving system (a database on QGIS). 2

The fact-finding survey was related to an in-depth work of archival research as well as plans for intervention on buildings.

In the case of Satrianum, a detailed survey of the site was carried out aiming at assessing all problems rigorously, and at reducing any risks of approximate and/or superficial assessments.

The aim of the database is to obtain a uniform corpus connecting different kinds of information – architectural, technical, typological, etc. – to deduce new data for interpretation.

The hierarchical organisational model of the Reference Units, developed by Gian Pietro Brogiolo, was chosen as a reference for the digital archive system of recording and relating the structural and functional data of the archaeological-architectural components, both with typological information – building typology, type of materials – the state of conservation and the relative forms of decay (Mangialardi and Sibilano 2011, 77-78).

The database consists of a preliminary section containing the personal data; another one with the archaeological-architectural data; a third part is dedicated to recording the various types of decay and the state of conservation; finally, a fourth part, the last one, proposes the recording of the structural vulnerability: this analysis is based on qualitative methods for the valuation of the masonry.

The collected information represents a solid basis for the elaboration of synthetic visions. Also, the analysis of the architectural artefact as the result of several constructive actions allows to evaluate both the state of conservation and the material characteristics and structural consistency.

Underlining the importance of creating a heterogeneous working group that can generate contributions from various points of view to the conservation project, it would be desirable that this preliminary work could be a starting point for an even more in-depth future work on Satrianum.

Working on a complex and structured analysis from an urban, functional and geomorphological point of view, relating to the existing structures and the routes to the level curves (for example, to identify and prevent the behaviour of the site during meteorological events of both moderate intensity and daily frequency as well as particularly violent ones) could increase the knowledge of the site under investigation.

The study of the state of conservation, especially for the possible degradation processes starting from the post-excavation phase, is a mandatory step in thinking and planning the future of archaeological sites.

In conclusion, it is our opinion that only adequate wide-ranging planning can constitute the essential first link of an integrated system. Nontheless the various issues, the needs and the available technologies may be considered in a multidisciplinary perspective.

(G.D.)

QGIS for the structure and development of spatial databases

To catalogue, organise and manage the data, we used a GIS platform, an essential tool for carrying out these types of operations interconnected with spatial analysis (Forte 2002; Bogdani 2009; Montagnetti and Rosati 2019; Noti 2021).

The focus of the project is the creation of a geographic database that allows documenting and systematising information through geolocation.

For the development of the project, we used the open-source software QGIS version 3.16 “Hannover” (http // wwwqgis.org) with GPL licence (GNU General Public License, commonly referred to by the acronym GNU GPL or simply GPL, is a licence for free software). QGIS, through various functions and a simple graphical interface, allows managing various input layers such as raster, vectors, and alphanumeric information. Furthermore, it allows expanding the workflow through different plugins.

The reference system used is Monte Mario / Italy Zone 2 (zone E) - Datum: Rome 40 - Projection: Gauss-Boaga the EPSG 3004 (European Petroleum Survey Group http://www.epsg.org); a cartographic system which uses the decimal metre to define coordinates, unlike geographic systems which apply coordinate expressions in degrees (https://docs.qgis.org/3.22/en/docs/gentle_gis_introduction/coordinate_reference_systems.html )

The construction of the database for the management of the USM of the Satrianum(PZ) site consists of two different types of data: rasters and vectors.

For the rasters, we used a cartographic base from the Google Satellite web tiles services, available through the Quickmap Service plugin (Licence CC-BY- SA, Creative Commons Attribution – Share-Alike 3.0). The other rasters were orthophotos taken by drone in jpg format with a 10×10 m pixels resolution, relating to the three main areas of the site: the cathedral (CF1, CF2, and CF3); the area of the first village (CF 23 and CF 104); the area of the second village (CF 59 and CF 75 and CF 79).

For the vectors, we chose a polygonal geometric layer within a geopackage; this format, based on OGC (The Open Geospatial Consortium – OGC) standards, is an information package that can be used as a database, an open compact format.

For this case study, a database was created in a GPKG file, which presents a single table organised to easily interact with the data and make queries using the SQL language (Ferrero 2004).

The first practical operation consisted of autoptic georeferencing the greater detail orthophotos of the three areas, using known points on the background map.

Through the “Georeferencer” tool, we used the transformation type “Helmert” (QGIS, like other GIS software, which has algorithms that manage the georeferencing of raster images. The algorithm is chosen based on the number of points we use, the quality of the graphic file, and the distortion or error in the final result. https://docs.qgis.org/3.22/en/docs/user_manual/working_with_raster/georeferencer.html), which offers the possibility to make roto translations and scale variations on the map with the “nearest neighbour “ resampling method.

After this georeferencing activity, we continued with the GPKG database, creating the polygonal vector layers and attribute tables. To organise the table’s field, we used, as a source, the criteria for the masonry techniques description of the ICCD (Criteria for the description of masonry techniques for the preparation of coded planning forms, ICCD – Central Institute for Catalog and Documentation, 2013 – translation from ICCD “Criteri di descrizione delle tecniche murarie per la predisposizione di moduli schedografici codificati” – and we have organised the items into four tabs:

the first group is related to personal data, like the names of the entity to be catalogued and digitised,

a second group contains the archaeological-architectural analysis data,

the third group is related to the USM conversation state,

the fourth and last to the structure vulnerability, as it is possible to see in Fig. 2 .

The last part related to the structural determination referred to the analysis based on qualitative evaluations of the masonry to obtain quantitative results of the mechanical characteristics (Borri et al. 2011). Therefore, it was worthwhile and necessary to consider the hierarchy of the referential realities, the Reference Units, that compose the concept of historic building developed by Gian Pietro Brogiolo (Brogiolo 1988).

To better define and organise the data groups, we used tabs within the table and widgets, as it is possible to see in Fig. 3 .

We can set these functions from the layer properties through the Attributes Module GUI, which works directly on the structure of the fields. To organise the tabs, we used the “Drag and Drop Designer” function of QGIS 3.16. Afterwards, we used the “value map” widget to facilitate the compilation of the table. The latter allows the formation of drop-down menus with different values, according to the database values, that can be entered in the respective fields. This is a modality that facilitates and limits the possibility of error in the structure rafting. Lastly, we used the “attachment” type of widget to insert the photos.

After structuring the table, we continued with the digitisation operations through the polygonal vector of the USM from the orthophotos. In the last phase, we continued with the categorisation of the entities based on the “Entità” field for printing and drafting tables. In this way, we can differentiate the geometries by colour, name and functionality.

We have printed three tables relating to the different architectural complexes with relative examples of a database query and with the “Atlas” function, a tool that offers the possibility of overcoming the static nature of the print composer and making composite prints in series.

The structuring of the workflow in QGIS has enabled extensive data management and precise organisation of the design operations.

(E.S.)

Survey and 3D GIS modelling

As it has already been said, by choosing this particular workflow – Luca Mandolesi, “OpenDroneMap: fotogrammetria open source | WebODM + QGIS + Blender”, May 17, 2021, video, https://www.youtube.com/watch?v=El4F38gcav0 – we utterly believed in the multidisciplinary approach to get an integrated system aimed at the valorisation of the archaeological site. We tried to obtain a foundation for a complex analysis that could serve different purposes: urban planning study, geomorphology, and architectural function (for a deeper insight into the role of 3D modelling in archaeological research, we would like to cite Hemon, Joanna 2008).

For these reasons, as a first fundamental step, we decided to obtain the geometrical acquisition of the archaeological site with its structures and its geomorphology. To do so, we proceeded to a 3D survey to generate a digital replica of the site. After having obtained permissions from the University of Basilicata and the office of the Superintendence of Archeology, Fine Arts and Landscape of Basilicata, part of the work team travelled to the site and carried out the operation on the field. An Unmanned Aerial System model DJI Mavic Pro was used to perform the acquisition of the photographs data set from the zenith perspective with two crawls. The UAS camera had a 12.71-megapixel matrix equipped with a 26 mm (35 mm equivalent) lens and permitted high-quality images to be captured. The survey was carried out by one operator who took care of covering the entire area and recorded sufficient overlaps for the photos; a second operator assisted as an observer. The drone was piloted at approximately 20 m to get a proper resolution of the whole site: two flights and more than 30 minutes were needed for the acquisition. The survey was carried out at noon to get the best lighting possible. For future campaigns, however, it would be desirable to continue with the terrestrial completion measures and concentrate on individual monuments.

As a second step, the images were processed with WebODM, an open source photogrammetry software for 3D spatial data generation in absolute coordinates. The software allows importing an image data set to be computed by an algorithm of structure from motion; afterwards, it matches bi-univocal correspondences among them to reconstruct the camera position and, therefore, the orientation in space. Finally, the software can elaborate a sparse point cloud, a dense point cloud, and a mesh. In our case, the geospatial references were obtained by UAS GPS which can already georeference the pictures – the average error consists of a value of 2 m ca. – nonetheless, it would be preferable for future developments to match the photogrammetry with Ground Control Points coming from a more precise topographical survey on the field. The interface allows us to regulate different parameters and obtain several kinds of outputs: in our case, we wanted to generate a Digital Surface Model, an orthophoto in raster format, a mesh in OBJ format, and the relative texture. To do so, we used the standard parameters that the software suggests, with a few exceptions: we set the parameters to get the orthophoto from the 3D texture and to raise the mesh size.

The DSM had a resolution of c. 0,24 m per cell and was imported in QGIS to elaborate contour lines (1 m wide) and save them as a shapefile., A section of the Digital Terrain Model was downloaded from the online dataset from TINITALY DEM  by the National Institute of Geophysics and Volcanology (INGV) to validate the correctness of the elaboration. The raster was imported in QGIS and used to elaborate contour lines as well, then exported in shapefile.

All these data sets were lastly imported into the open source software for 3D modelling, Blender. We immediately turned on the add-on BlenderGIS, which allows working in an absolute coordinate system 3D space. At this point, it was possible to import the OBJ for the archaeological site and its texture and the shapefile of its contour lines. We also imported the shapefile of the TINITALY DEM contour lines, which were then interpolated to obtain a mesh through the Delaunay method: the two altimetry data sets matched satisfyingly, so our elaboration was validated.

Afterwards, we converted the polygons related to the walls from the geopackage to the shapefile format, and then we imported them: these were organised inside the outliner in different “collections’’ (groups of layers) according to a chronological principle to allow a more handful consultation of the SU. Figure 4 allows a general overview of the final outcome of the work inside Blender.

In our opinion, the data set that we obtained on the field and organised in a GIS database inside a 3D modelling software could reveal as utterly useful from different and multidisciplinary perspectives, for which we hope the works on this beautiful site could be enhanced and carried on in the future.

First, it gives a geometrically and geographically precise model to be used for architectural and landscape project design, e.g. by architects and engineers teams to improve the fruition of the site for the audience. It would be extremely helpful for designing better visiting ways all along the site, preventing geomorphological instabilities for the remains, or designing new museum elements for the didactic of the site.

Secondly, the dataset provides precious information for a topographical and orographic study of the site to better understand the ancient centre and its relationship with the territorial surrounding context. It would be desirable to go further in this way, enlarging the scale and having better and more interesting developments in this landscape archaeology.

Thirdly, the digital output could be useful to be used for the enhancement of the site and its digital communication, for example, from a museum or a tourist perspective. Again, it would be preferable for the future to put this case on a larger scale in a regional network.

Finally, the digital analysis, along with the site inspection and its organisation in an interactive virtual database, gives a fundamental stratigraphic comprehension of the complex structures and the ancient buildings: this could be fundamental for accurate restoration design projects and the reinforcements of the structures as well. Nevertheless, such a data set could be likely implemented in further digital and scientifically accurate elaborations: e.g., the case study would be perfect for development according to the Extended Matrix paradigm (Demetrescu 2018), which would give a scientifically precise reconstruction of the fortified site in its historical development.

(A.S.)

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1

We want to thank the scientific director of the excavation, Francesca Sogliani, and SABAP-MIC, with particular reference to Simona Di Gregorio, who have allowed this work to be carried out.

2

The archaeological conservation project for Satrianumrepresented the undersigned’s thesis entitled “Archeology and restoration of monuments. Prospects for research in the medieval fortified site of Satrianumin Basilicata” (Supervisor: Francesca Sogliani; co-supervisor: Filiberto Lembo). Furthermore, the project was introduced to the Superintendence of Archeology, Fine Arts and Landscape of Basilicata. The project particularly concerned the cathedral and some buildings of the first and second village of the archaeological site.