GENERATION OF GIGAPIXEL ORTHOPHOTO FOR THE MAINTENANCE OF COMPLEX BUILDINGS. CHALLENGES AND LESSON LEARNT

This study is part of the “Milan Cathedral Survey project”. It is a three years long research project with the aim of surveying the entire cathedral in 3D with different techniques (mainly photogrammetry and laser scanning). The goal is to renew the architectonic drawings (sections elevations and plans) to obtain new updated and certificated measurements of the cathedral, as requested by Veneranda Fabbrica del Duomo, and to produce the basis on which to build a future 3D BIM (Building Information Model) system implementation. In this paper, we would like to examine in depth the survey process of the exterior elevations of the cathedral carried out using photogrammetry as the main survey technique for orthophotos production. The case studies here presented have the goal of underlying challenges, discussing decisions and approaches, describing the followed pipeline and of defining a standard method that can be followed to produce gigapixel orthophotos of complex cultural heritages.