Geometric Survey for the Structural Assessment of the Architectural Heritage: the Case of the Cupola of the Baptistery of S. Giovanni E Reparata in Lucca

The present work reports an experimental combined application of laser and photogrammetry techniques. The current research aims to the testing of both innovative (scanning instruments) and classical survey techniques applied and architectural and structural objects, as to evaluate their interoperability for a conjunct usage with static purposes. The object of the study is the brick masonry Renaissance cupola of the ancient baptistery of S. Giovanni in Lucca, constructed over a square basis of 14 m side at the level of 15 m from the floor. The main features of this cupola reside in its shape, remarkable dimensions and construction technique. Authors have carried out a survey aimed at the study of the shape of the intradox surface as well as at the reconnaissance of the hidden structures (safety arches in the West-facing webs) and of the crackings, each and every one necessary elements for a static check. Terrestrial laser scanning has enabled fast, smooth surveying of the coordinates of many points of the surface. An accurate choice of the points and their subsequent elaboration with specific software have led to the comprehension of the shape and of the geometrical irregularities as well as the definition of an ad hoc interpolating surface, actually a mesh, for static checks. The photogrammetric techniques, together with all the information concerning the surface masonry patterns, help to understand the construction phases and to identify, characterise and locate the existing damages. Thus, the combination of different survey techniques has shown its effectiveness in the case of the static assessment of architectural structures.