THE AMBON OF SANT'ANDREA IN PISTOIA: A COMPARISON BETWEEN LASER SCANNER AND PHOTOGRAMMETRIC DIGITIZATION OF MARBLE SURFACES

The ambon by Giovanni Pisano in the church of Sant'Andrea in Pistoia (Italy) consists of a hexagonal platform raised on slender columns standing on bases and sculptures with different heights. In the 17th century, it was disassembled and placed in a different location and, also for this reason, is currently in an endangered condition. As part of a multi-disciplinary programme of investigations and monitoring, a 3D survey was requested. The challenging aspect of the survey is related with the material of the work of art, as it is completely made of different kinds of white and red marbles. These materials are translucent and light diffuses through them, so the laser beam scatters beyond the surface and biases measurements in an unpredictable way. Tests were carried out, comparing two scanners with different characteristics and digital photogrammetry. The results show significant differences between the three technologies, identify the best solution in relation to the desired objectives, and highlight how different acquisition techniques affect the suitability of models for subsequent applications.