Modelización 3D de estructuras y depósitos arqueológicos como método de documentación y divulgación: el caso del conjunto arqueológico de San Esteban (Murcia, España)

Abstract

[ES] El conjunto arqueológico de San Esteban se localiza en el actual centro urbano de la ciudad de Murcia. Se trata de un amplio espacio de origen andalusí que formaba parte del antiguo arrabal de la Arrixaca, un barrio extramuros que parece conformarse durante el siglo XI y que constituyó una parte importante de la ciudad medieval de Murcia. El proyecto de investigación realizado entre los años 2018 y 2020 en el conjunto arqueológico de San Esteban, bajo el convenio firmado entre la Universidad de Murcia y el Ayuntamiento de Murcia, conllevó una serie de campañas de excavación arqueológica en diferentes puntos de este enclave. Se intervino en cuatro sectores que se mostraban especialmente relevantes desde el punto de vista funcional y de la articulación urbana de este entramado: los edificios conocidos como Recinto I y Recinto II , el oratorio y la maqbara. El proyecto fue concebido desde una perspectiva interdisciplinar, jugando un papel clave la incorporación de nuevas tecnologías en el proceso de documentación de la excavación. La metodología llevada a cabo se basó en los procedimientos fotogramétricos de alta precisión y de seguimiento diacrónico de la intervención arqueológica, teniendo como objetivo la elaboración de un registro gráfico que afectaba tanto al plano bidimensional (2D) como al tridimensional (3D). Para su correcta elaboración se combinó el uso de vehículos aéreos no tripulados (UAV por sus siglas en ingles) y de instrumental topográfico. Como resultado, este registro permitió confeccionar toda una serie de planimetrías vectoriales, ortomosaicos y recursos 3D de cara a su posterior análisis y de divulgación arquitectónica y material de los elementos arqueológicos intervenidos. Este trabajo desarrolla los procedimientos metodológicos llevados a cabo, una serie de propuestas de análisis y los resultados obtenidos en el marco de aplicación de las nuevas tecnologías en el campo de la arqueología.

[EN] The research project carried out between 2018 and 2020 at San Esteban archaeological site (Murcia, Spain), under the agreement signed between the University of Murcia and the Ayuntamiento of Murcia, was realized by a series of archaeological excavation campaigns in different parts of this enclave. Of the sectors involved, we have chosen the four most relevant ones: the buildings known as Recinto I and Recinto II, the "Oratory" and the cemetery or Maqbara (Fig. 1). The objectives of the research project were the review and diagnosis of the state of conservation, the interdisciplinary study, the adoption of consolidation measures and the temporary exposure of the sectors involved (Eiroa et al., 2019; 2021). San Esteban archaeological site is located within the current urban centre of the city of Murcia. It is a good example of medieval Islamic urban design in a part of the old suburb of Arrixaca, a neighbourhood outside the walls of the city that seems to have been formed during the eleventh century. The graphic record in archaeology has been an intrinsic part of the discipline since its inception (Caballero, 2006). Photography and archaeological drawing have been the main ways of documenting an archaeological excavation with the double objective of achieving a topographical reconstruction and ordering the material remains by means of a stratigraphic sequence. Photogrammetry has become one of the main techniques in archaeology and is a great support in the topographic and planimetric survey of high precision and graphic representation. The use of drones or unmanned aerial vehicles (UAV) (Korumaz & Y?ld?z, 2021), high-resolution digital cameras and the appropriate software has enabled their application in numerous cases, generating extensive quality records, as can be seen in the field of medieval archaeology (Enríquez et al., 2020; García-Molina, González-Merino, Rodero-Pérez & Carrasco-Hurtado, 2021; Ruiz, Gallego, Peña, Molero & Gómez, 2015) or in the study of medieval buildings. In the fieldwork at San Esteban archaeological site, a series of topographic instruments and photogrammetric software in a 4D sequence have been used, allowing not only the documentation in the plan of the archaeological structures, but also the location of the deposits in a stratified sequence. For the generation of these diachronic three-dimensional models, the Agisoft Metashape software was used, based on the SfM (Structure from Motion) technique of geometric analysis of clusters of pixels from photographic perspectives with different parallaxes. This technique has become an important methodological dynamic in the archaeological record (Maldonado, 2020: 196-203), improving the work of topography in the field of geomatics (Marín, 2020). The results obtained have allowed the creation of a vector plan of the documented structures and the registration through the SfM photogrammetry of elevations (Fig. 6) and of the depositional process of the sectors involved (Charquero, 2016; Semeraro, 2008). As an example of this methodology, a practical case within the building known as Recinto I is highlighted (Fig. 7). This exercise carried out in the Espacio 4 has made it possible to measure the development of the excavation by continuously recording the activity at a specific point of the site. Also, a detailed delimitation of the extension and volumetric shape from the contact surfaces of a stratigraphic unit has been made, reflecting the physical aspects of the deposit itself at a visual level (Fig. 9). It is a method which emphasises the documentation of the depositional process from a three-dimensional and orthophotographic perspective of the strata (Montalvo, Dyrdahl, Cantisani, Fabririis, & Vinci, 2020; Orengo, 2013), allowing greater detail in the delimitation and shape of the excavated stratigraphic units and assemblages, either synchr