From Multi-Sensor Survey to a Multi-Scale Geospatial Digital Twin Foundation of a Historic Hill Town: Fiumefreddo Bruzio, Southern Italy

Historic hill towns require geometric information capable of relating urban morphology, construction features, and structural details within a common spatial and semantic framework. This paper presents a multi-sensor, multi-scale geomatics workflow for establishing an integrated geospatial information framework for the historic centre of Fiumefreddo Bruzio in Calabria, southern Italy. A control network of 38 points provided the spatial reference for UAV and terrestrial photogrammetry, six SLAM trajectories, and 270 static laser scans covering five buildings. Point clouds generated by Structure from Motion and range-based sensors were co-registered in the RDN2008/UTM zone 33N coordinate reference system and used to produce orthophotos, digital terrain and surface models, contour lines, textured meshes, and building-scale drawings. These products were organised within an interoperable geospatial information system based on persistent links between settlement-, aggregate-, building-, façade-, space-, and macroelement-level entities. The framework also supported structural characterisation and seismic vulnerability assessment at building and urban scales, linking building screening and potential local mechanisms to their spatial interpretation. The resulting survey-based digital model supports conservation documentation, seismic screening, and street-network analysis, while providing the foundation for future digital twin development rather than an operational implementation. The study offers a transferable acquisition-to-information workflow, preserving data provenance and metric quality for risk-informed management of historic settlements.