Reviving the Lost Space. Digital Anastylosis and Augmented Reality Methodology for the Immersive Reconstruction of the Retrochoir of Tarragona Cathedral

The choir of Tarragona Cathedral, installed in the centre of the nave in the 12th century, underwent the partial dismantling of the retrochoir in 1963, a trend that has continued into the past century, when retrochoirs began to be removed, creating the open space that the temple’s new uses have demanded. In this case, however, in addition to preserving the two rows of perpendicular chairs, the dismantled elements were repositioned in various parts of the presbytery. The restoration of missing architectural components within their historical context presents a challenge for heritage conservation and interpretation. This study confronts this difficulty by employing a methodology that integrates digitization, virtual archaeology, and augmented reality (AR) to realistically reconstruct the Gothic retrochoir of Tarragona Cathedral. The procedure commences with the photogrammetric acquisition of the scattered fragments, producing high-precision 3D models. These are constructed by virtual anastylosis, grounded in the examination of historical sources and material evidence. The resultant model is integrated into a geolocated augmented reality application that overlays the reconstruction at its precise location within the cathedral nave, facilitating visualization via mobile devices. This work's primary contribution is a comprehensive workflow that links the documentation of dispersed elements with in-situ experience, illustrating that AR effectively bridges academic research and public perception, significantly enhancing the spatial comprehension of the lost monument.