Recovering a collapsed medieval fresco by using 3D modeling techniques

Abstract. The paper presents the results of a reconstruction of the 3D model of a dome and of a medieval fresco, collapsed after an earthquake and now reconstructed in significant portions, to offer to the visitors a possible reconstruction of the lost masterpiece of medieval art. After the earthquake the collapsed dome was replaced by means of a concrete sphere connected with the survived portions of the old dome’s timber. The old dome shape and the fresco were virtually reconstructed thanks to a set of historical pictures obtained by Italian, USA and German archives; those images have been calibrated and oriented by using modern digital photogrammetric approach and a realistic 3D model of the old inner surface of the dome has been realised. By using a LiDAR survey the 3D model of the apse and of the dome, has been set up and the boundaries between original and new structures have been reconstructed by visual evidences.The new dome has been virtually erased and the old dome with the fresco 3D model inserted allowing the reconstruction of the apse as it was before the earthquake. This virtual 3D model has been used to realise a 1:1 scale model of the old dome where the restorers fit some parts of the old fresco fragments recovered just after the earthquake, cleaned and classified. The fresco images correctly oriented inside the reconstructed dome have been projected on plane surfaces by using azimuthal orthographic projections of small portions of the dome in order to reduce the geometric deformations and to allow the mosaicking of these small planes onto a spherical surface.