Digital Twins for Medieval Monuments: Requirements from Art Historians and Technical Challenges for Analysis and Restoration

Research on Visual Computing and Cultural Heritage naturally requires the involvement of multidisciplinary teams comprising art historians and technical experts. Despite the vast literature on digital 3D models in support of Cultural Heritage, the field is so rich and diverse that specific projects often imply distinct, unique requirements which often challenge the computational technologies and suggest new research opportunities. In this paper we discuss the requirements and technical challenges within the EHEM project, an ongoing research program for the analysis, documentation, interpretation, restoration, and communication of medieval artistic heritage. We describe the three monuments that serve as test cases for the project, all of them with a rich history in terms of architecture and paintings. We discuss the art historians' view of how digital models can support their research, the expertise and technological solutions adopted so far, as well as the technical challenges in multiple areas spanning geometry and appearance acquisition, color analysis and restoration as well as the representation of the temporal transformation of the architecture and the paintings.