High-accuracy 3D modeling of cultural heritage: the digitizing of Donatello\´s "Maddalena"

Three-dimensional digital modeling of heritage works of art through optical scanners, has been demonstrated in recent years with results of exceptional interest. However, the routine application of three-dimensional (3D) modeling to heritage conservation still requires a systematic investigation of a number of technical problems. The paper describes the process of acquiring a 3D digital model of the Maddalena by Donatello, a wooden statue representing one of the major masterpieces of the Italian Renaissance which was swept away by the Florence flood of 1966, and subsequently restored. The paper reports all the steps of the acquisition procedure, from the project planning to the solution of the various problems due to range camera calibration and to optically noncooperative material. Since the scientific focus is centered on the 3D model´s overall dimensional accuracy, a methodology for its quality control is described. Such control has demonstrated how, in some situations, the ICP-based alignment can lead to incorrect results. To circumvent this difficulty, we propose an alignment technique based on the fusion of ICP (iterative closest point) with close-range digital photogrammetry and a noninvasive procedure in order to generate a final accurate model. Detailed results are presented, demonstrating the improvement of the final model, and how the proposed sensor fusion ensures a prespecified level of accuracy.