Applying Photogrammetric Techniques to Determine Façade Decays: The Case Study of Zisa Palace, Italy

The aim of this paper is to present a non-destructive method for façade decay analysis and quantifying with many ap-plications to architectural heritage (monuments, historical buildings, etc.). The proposed methodology is based on the combination of topographic surveys, digital photogrammetry and image processing techniques by means of four control points and one photography of the target façade, at least, that become metric rectified image at any plane defined by the user. It is possible to quantify any physical characteristic of the surface of a building as well as alterations on its surface that produce deviations from flatness. The Bundle adjustment was applied to a 2D reconstruction algorithm instead to a 3D reconstruction algorithm to control the flatness of a façade of a monument, the Zisa Palace in Palermo (Italy). Sig-nificant deviations of the points in the vicinity of the edge left of the façade with respect to the coordinates of the points of support were evidenced, indicating that the overall facade of the monument is not a flat surface. The results, with an estimated 10–3 accuracy, suggest that a structural failure in an area of the façade may be occurred after the restoration work or, alternatively, that such restoration was not performed successfully in that area.