Hi-res photogrammetry teams up with photometry to unveil hidden features: The case study of the St. Ambrose’s so-called dalmatic

The article presents the methodology used to photogrammetrically detect a three-dimensional model of the so-called Dalmatics of Sant’Ambrogio, preserved in the basilica of the same name in Milan, and obtain a high-resolution flat representation of the designs that the warp and weft form on the damask fabric. The methodology developed, in addition to exploiting the well-established stereo-photogrammetry techniques for the very high-resolution survey of objects, solved the problem of detecting the figures present on the fabric, but visible only with specific directional lighting. By acquiring different images from each shooting position, each characterized by a different lighting direction, it was then possible to select from the models obtained from these images those portions that allowed the figures to be best viewed