The Challenge: Reaching the Unreachable
Some of the most extraordinary archaeological sites lie far beyond ordinary reach. The Xlendi shipwreck, off the coast of Gozo (Malta), rests at a depth of 110 metres — accessible only to a handful of technical divers equipped with rebreathers and supported by extensive logistics. This 7th-century BC Phoenician vessel, one of the oldest known wrecks in the Western Mediterranean, has been the subject of over a decade of photogrammetric surveys, producing more than 30,000 underwater images.
How can archaeologists, students, and the public explore such a site without ever getting wet? Virtual and augmented reality offer a compelling answer.
Left: photogrammetric survey at depth — Right: excavation at 110m with water dredge. Photos: J. Wood, K. Hyttinen
From Seabed to Screen
The workflow bridges the physical site and its digital twin. Thousands of underwater photographs are processed through photogrammetric pipelines to produce dense, coloured 3D point clouds containing over 100 million points. These models are then enriched with archaeological knowledge through a formal ontology (Arpenteur), making every artifact queryable via standard semantic web protocols (SPARQL).
The result is not merely a 3D visualisation but a true knowledge-connected digital twin — where pointing at an amphora reveals its typology, excavation history, and links to comparable objects across the Mediterranean.
Virtual Reality: Diving Without Water
Using an HTC Vive headset and Unreal Engine, researchers can immerse themselves in the Xlendi wreck site as if they were diving at 110 metres. The coloured point cloud is rendered in real time — no mesh generation required when the density is sufficient. The navigation mimics a diver's movement: vertical displacement controlled like a lung-ballast system, free exploration in all directions.
The Xlendi wreck site rendered as a dense coloured point cloud in the VR environment
A virtual laser pointer lets the user select any artifact in the scene. The system queries the ontology in real time, displaying archaeological metadata, typological classification, and links to similar objects in external Linked Open Data repositories.
A timeline feature allows researchers to travel through the excavation history: seven survey campaigns from 2009 to 2020 can be compared, watching the terrain evolve as artifacts are progressively uncovered, recovered, and replaced by high-resolution scanned models.
Augmented Reality: The Wreck on Your Table
For a more accessible and collaborative experience, the XlendiAR application runs on standard Android tablets. Using ARCore for spatial tracking, the app projects the complete 3D model of the wreck site onto any flat surface — a table, a desk, a museum floor. Multiple users can walk around the model simultaneously, each seeing it from their own perspective.
The XlendiAR app: timeline navigation between 2014 and 2018 survey states on an Android tablet
Like its VR counterpart, the AR application is connected to the knowledge base. Tapping on an amphora displays its archaeological record. A built-in chat system enables remote collaboration — originally designed for dive team debriefings, it now allows experts worldwide to discuss the site while viewing the same 3D model.
The tablet becomes a window into a virtual space that overlaps point by point with the real space in which the user moves — a modern echo of Borges's 1:1 scale map, where the representation is no longer a simplification of reality but a complete substitute for it.
Based on: Nawaf, M., Drap, P., Ben-Ellefi, M., Nocerino, E., Chemisky, B., Chassaing, T., Colpani, A., Noumossie, A., Hyttinen, K., Wood, J., Gambin, T. & Sourisseau, J.-C. (2021). Using virtual or augmented reality for the time-based study of complex underwater archaeological excavations. ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences, VIII-M-1-2021, 117–124. doi:10.5194/isprs-annals-VIII-M-1-2021-117-2021