I Sistemi Coordinati per il Rilievo Integrato dei Patrimoni Archeologici: il Caso delle Terme di Baia

This paper presents an integrated, multi-scale survey approach applied to the Archaeological Park of the Baths of Baiae, one of the most complex and stratified sites of the Phlegraean Fields in Southern Italy. The research combines GNSS and total station topographic surveys, terrestrial laser scanning (TLS), aerial photogrammetry through Structure from Motion (SfM), SLAM-based mobile mapping, and structured light scanning (SLS), in order to generate a comprehensive, georeferenced and highly accurate three-dimensional digital twin of the site. The methodological framework was designed to overcome the intrinsic limitations of each individual technology by exploiting their complementarity: GNSS provided the geometric framework through a robust network of Ground and Quality Control Points; TLS ensured millimetric precision in the acquisition of complex architectural and underground environments; drone-based photogrammetry enabled extensive coverage and the reconstruction of the broader territorial setting; SLAM facilitated the exploration of inaccessible hypogea; and SLS documented portable artifacts and decorative details at sub-millimetric resolution. The result is a unified, navigable, and updatable 3D model, which serves as both a scientific archive and a dynamic tool for conservation, monitoring, and communication. The digital twin is not conceived as a static repository, but as an open and interoperable platform, capable of integrating further datasets—structural analyses, environmental monitoring, historical sources—and interacting with HBIM, GIS 3D, and immersive VR/AR applications. Particular attention was paid to methodological issues such as data registration, georeferencing stability, drift management in large TLS campaigns, and integration between range- and image-based models. The adopted workflow, validated across more than 50 field sessions over a two-year period, demonstrates the feasibility and robustness of coordinated survey strategies in challenging archaeological contexts affected by geomorphological phenomena such as bradyseism. The Baths of Baiae are here framed within a broader research initiative known as the “Constellation of Water,” a thematic network of hydraulic and thermal monuments in the Phlegraean Fields—including Piscina Mirabilis, Centocamerelle, the so-called Tomb of Agrippina, and the Serapeum of Pozzuoli. This network represents one of the pilot cases of the SPLASCH project (Smart Platform and Applications for Southern Cultural Heritage), which aims to build a digital infrastructure for the documentation, management, and valorization of cultural heritage in Southern Italy. Within this framework, the Baiae survey plays a strategic role in testing the interoperability of multi-source datasets and the creation of interconnected digital twins. Beyond scientific documentation, the project emphasizes accessibility and cultural dissemination. The integration of high-resolution orthoimages, textured 3D meshes, and interactive point clouds into platforms such as Scene2Go and Sketchfab enables remote exploration of inaccessible or submerged areas, immersive experiences for the general public, and advanced research tools for specialists. Digital models have also been transformed into tactile 3D prints for visually impaired visitors, enhancing the inclusivity of cultural heritage experiences. The potential of VR/AR environments, supported by game engines like Unreal, allows users to virtually walk through reconstructed Roman thermal spaces, perceiving architectural volumes and decorative details otherwise lost. This study also highlights the methodological continuity with previous surveys, such as the Forma Italiae campaign of the 1970s, while significantly upgrading the workflow through digital technologies, data interoperability, and dynamic information management. The Baiae case thus exemplifies how integrated surveying can produce a scientific and operational resource of high value, addressing multiple purposes: conservation planning, historical interpretation, virtual dissemination, and community engagement. The proposed workflow, replicable in other archaeological contexts, confirms the potential of digital twins to bridge past and future, enabling a sustainable, inclusive, and participatory approach to cultural heritage.