Integrated surveying techniques in cultural heritage documentation

This paper is focused on integration between laser scanning data, CAD modelling and photogrammetric data collected during the survey of one façade of the monument called “Quattro Canti” in the historic centre of Palermo. The investigation has been directed to the production of a 3D photorealistic model of the monument. The “Quattro Canti” monument is formed by four cylindrical façades facing the square where the older streets of Palermo intersect; each façade has a symbolic reference to one of the seasons and is divided in four levels. The façade called “Canto dell’Autunno” has been surveyed both with laser scanning and with photogrammetric techniques. Laser scanning data have been collected in a single scan with a resolution of about 7 mm; stereoscopical photos have been taken with a film camera Rollei 6006; all data have been referred to a topographic reference system. The investigation has been restricted to the third level of the “Canto dell’Autunno” façade. The surface model has been built from laser scanning data with an automatic triangulation process; the inconsistent parts have been substituted using CAD models and points extracted via photogrammetric image matching. Photogrammetric processes have been used also to produce a 3D orthophoto. In order to produce a 3D photorealistic model of the investigated area, photogrammetric texture mapping has been performed with a commercial software.