FROM 2D (TO 3D) TO 2.5D – NOT ALL GRIDDED DIGITAL SURFACES ARE CREATED EQUALLY

Abstract. The surface of most heritage objects holds important clues about their creation. To answer specific research questions about a 16th-century mural painting located in the Bischofstor of Vienna's St. Stephen's Cathedral, the three-dimensional (3D) geometry of the entire painted surface was digitised in minuscule detail using thousands of overlapping photographs. Although this article provides image acquisition and processing specifics, it aims to assess which image-based modelling workflow can achieve the most detailed, noise-free, two-and-a-half dimensional (2.5D) raster surface of this mural painting. Other than their full 3D counterparts and in contrast to the focus of most academic research, 2.5D raster surfaces are ideally suited for visualising and analysing sizeable, detailed surfaces. They are, therefore, still the preferred surface encoding of many heritage projects that want to leverage digital surface approximations to further heritage insights (and not just use them as mere eyecatchers). In the end, only a combination of different 2.5D rasters was able to accurately represent the variable surface of this mural painting with the right amount of spatial detail.