From survey to model and return. The case of the Parma Baptistery.

Although this is not always the common practice, the survey should be an essential preliminary stage to any operation of restoration, enhancement and promotion of cultural heritage. Today, various surveying techniques make it possible to collect large amounts of data quickly and to provide a complete three-dimensional representation of extremely complex artefacts. In fact, 3D models allow a much richer description than traditional 2D representations. However, these survey techniques (laser scanner and photogrammetry above all) necessarily imply that the data that must be elaborated during the processing phase increase dramatically. It is therefore essential to identify methods and workflows that allow to find a compromise between the richness and completeness of the survey data and the problems inherent in the costs and times of execution of the modelling operations. The problem is further heightened by the fact that the importance of historical monumental architecture inevitably requires the use of different techniques integrated with each other, the production of documentation at different scales with different levels of detail and the creation of a 3D model that has the ability to be used for different purposes. This paper describes the survey of one of the most important medieval monuments in northern Italy, the Parma Baptistery, with a special focus on the phase of data restitution. The integrated survey campaigns conducted in recent years have aimed to describe the building in its totality: from the scale of the architecture to the detail, passing through the description of the pictorial cycle that characterizes the interior. This case study represents a moment of reflection, at least for those who wrote it, on the validity of the methods and techniques to be used for the creation of a complete 3D model of a complex historical monument.