Integration of Laser Scanning and Photogrammetry in Architecture Survey. Open Issue in Geomatics and Attention to Details

In the last decades, surveying methodologies related to Geomatics applications in the Cultural Heritage field have undergone a constant evolution. The first innovation has surely been the development, in the 1990s, of laser scanning systems. These are able to survey the coordinates of millions of points of architectural objects with sub-centimeter precision and high density. The second breakthrough, starting from the 2000s, is the “second youth” of photogrammetry methodologies. The “new photogrammetry” yielded tools and methodologies able to provide low-cost 3-D models, featuring photo-quality textures, suitable for very high scales reconstructions. Although both methodologies are fairly consolidated, one interesting research topic is the integration of the different methodologies aimed at optimizing results as regards both logisticscosts and attainable precision levels. The paper focuses on the latter topic, showing the methodological approach followed for the outer face restitution for the North transect of the Pisa Cathedral at 1:20 scale, as requested by the staff in charge of maintenance and restoration. In detail, the precision problems for the least accessible parts and for the transitions between orthogonal and parallel surfaces, relative to the average direction of the camera axis, are discussed. Finally, the processing methodology used for restitution at the same scale of the development of curved masonry sections, is presented. While compiling these documents for architecture study and documentation, attained geometric precision and texture resolution are checked, with a particular focus on how segmenting model sections with primitive surfaces can improve these parameters, and as a consequence also the final restitution.