3D GEOMETRIC ANALYSIS OF THE FAÇADES OF GOTHIC BUILDINGS IN VENICE: EXAMPLES OF 3D MODELLING Francesco Guerra, Caterina Balletti, Cecilia Stevanin, Paolo Vernier Università Iuav di Venezia - CIRCE Laboratorio di Fotogrammetria S. Croce 1624, 30135 Venezia guerra2@iuav.it , balletti@iuav.it KEY WORD: architecture, laser scanner, warping, analysis, surface ABSTRACT The Photogrammetry laboratory at CIRCE is conducting a research campaign to identify a procedure for survey and representation of warping on the façades of Gothic-era Venetian buildings. With respect to an ideal plane, the warpings can be caused by to two different sources: the first, the object of this research, involves a hypothesized “entropiombo” of design, in other words, a deliberate slope of the plane of the facade inward. This hypothesized design warping is added to the second reason, represented by the warpings due to subsidence and settling, either local or generalized, of the buildings which always appear in Venetian structures. The result is a complex geometric configuration which is quite difficult to read. The studies conducted till now have resulted in very important observations relating to the individual cases, but a comprehensive investigation has not been done on a statistically consistent sample of façades, which could help identify construction "customs". To date, the geometric analyses have been based on a model of the warpings achieved by a substantial number of vertical and horizontal profiles, selected in the most relevant areas of the façade. Survey by topography or photogrammetry proved to require an inordinate amount of resources, which is why the investigations have always involved a fairly limited number of buildings. Today, the availability of laser-scanner instruments have made it possible to reduce the acquisition times of the data and automate extraction of the profiles, but most importantly, have made it possible to create a descriptive 3D model of the surface. The paper describes the survey methodology used in the research (topographic support, laser-scanning, photoplanes and orthophotos) and the representations that have been formulated to describe the building surface (models of warping) through exemplification of the experiences. The façades of the many Gothic buildings in Venice, especially buildings that were constructed directly on the canals, present a significant degree of entropiombo of the vertical wall surface. In other words, the structure is not quite a vertical plane but rather, tends toward a slightly sloped surface. The reason behind this seems to be the construction technique used in these buildings: in the local construction culture, the walls of the façade were not anchored to the masonry framework. Presently, this phenomenon is the subject of analysis and study by historians and restorers which have found the slope to be a "design" choice and are attempting to identify the construction "traditions" of the times, rather than the "rules" of construction. fig.1 Scheme of the construction tecnicques of gotic façades and movement ipothesis of venitian buildings. Thus, the research team launched a study entitled "Organization of the knowledge and diagnostics for conservation of the historic Venetian building tradition" (CORILA research programme), financed by the IUAV which entails that the CIRCE photogrammetry laboratory identify and test the methods of survey and representation for a widespread representation of the warping phenomena of the Venetian façades in the study. fig. 2 Some buildings localization on Venice map