INTEGRATED 3D-DATABASE FOR DIAGNOSTICS AND DOCUMENTATION OF MILAN’S CATHEDRAL FAÇADE

The Gothic Cathedral of Milan is one of the most important italian monuments: its façade is 65 m high with 12 spires and has a surface of about 4500 m, rich of Candoglia marble carved decorations and sculptures. The conservative restoration and maintenance of so complex an architectural structure needs advanced computerized tools for storing, analysing and updating all the produced data. A multidisciplinary approach was adopted to build an integrated tridimensional database (63 GByte). The basis is a stereoscopic model (by StereoView SVPlotter AC software) which makes it possible to navigate through many photograms all over the façade, to measure accurately the dimensions of architectural details and to draw structures with a millimeter precision. In this way a tridimensional 1:20 CAD model of the façade was created, in which every block is a single geometric unit. Moreover, a specific software tool was developed to insert photos, documents and texts in a geo-referenced way and to constantly update them. A thematic layer organization was used to store and integrate the architectural information and the diagnostic investigation results. The former includes, for example, the material distribution (i.e. marble, stuccos, metal cramps), missing parts, removed and replaced blocks, restored areas etc. The latter consist of the non destructive in situ analysis data, concerning both the surface (XRF, colorimetry, thermography) and the bulk (georadar or GPR), not only for pre-restoration diagnostics but also for assessing the quality of effected operations. In particular, a specific software, called ETRadar (AutoCAD application), was created for structural analyses: it makes it possible to insert 3D radargraphic maps, to draw inner fractures and cavities revealed by georadar inside the masonry and to assign a volume to every stone block, as determined by GPR. In this way critical areas were localized and helped the definition of the working plan. The restoration work is still in progress.