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- Territory and drystone walls. Comparative of case studies in central and southern PortugalPublication . Marçal Gonçalves, Marta; Prates, Gonçalo; Pérez-Cano, María Teresa; Rosendahl, Stefan; I. Lombillo; H. Blanco; Y. BoffillSince becoming settled, Man had the need to shape the territory in his benefit, gaining ground for agricultural activity. Drystone walls were the way found to overcome sharp slopes. The way these walls are arranged in the territory is not random, as it may seem at first glance: they are disposed in the best way to facilitate the agricultural activity, taking into account the natural factors of the territory where they are located, such as orography, climate or geology. Taking as study cases two regions in Portugal under slightly different climate regimes, one located in the Algarvian Barrocal and the other located in the Center, we intend to compare and advance with explanations as to the way drystone walls are disposed and their relation to the territory. To achieve the objectives bibliographical and photographic studies, as well as interviews with the inhabitants of these areas, and cartographic and field surveys were carried out. Whereas the purpose, materials and construction characteristics were achieved by the previous, their disposition and relationship with the orography were carried out by the latest. Particularly, field surveys were made by digital stereophotogrammetry applied to several overlapping nadiral photographic images from different perspectives acquired by an unmanned aerial vehicle along its flying pathways that allowed for very high-resolution geographic data. Where such surveys were not made, cartographic data were used instead. Through the dissemination of such vernacular heritage, it becomes valued and known. In this way, people will attribute cultural and patrimonial value, protecting it, especially the local population that tends not to attribute any value to this “minor” heritage, contributing to its disappearance. There are still not much works about this subject in the areas analyzed here, so this paper has an added value, in order to disseminate and create added value to these kind of heritage.
- Silves bridge geometric model via structure-from-motion: tool for heritage digital catalogsPublication . Prates, Gonçalo; Marçal Gonçalves, Marta; Lopes, Ana; Laranja, RobertoThe old bridge in Silves, Portugal, has five perfectly formed arches extending over the Arade river with about 76 meters long built of local materials. In the 14th century this structure was rebuilt on the location of a previous structure built when Silves was the Moorish capital between the 8th and 13th centuries occupation of the Algarve. Though a Roman road might have crossed this area, there is no medieval descriptions mentioning a bridge in Silves, still it is also known as the Roman bridge.After interventions in the 14th, 17th, 18th and 20th centuries, the bridge was classified as monument of public interest and became pedestrian-only and frequently evaluated for its risk of collapse. Stereo-photogrammetry is a recognized surface reconstruction tool applied for almost one century, where from several overlapping images of the surface a 3D model can be obtained. Contrasting with classical stereo-photogrammetry, Structure-from-Motion (SfM) is a nearly automated compilation of digital imagery processing strategies that solve for camera position and surface geometry using matching features identified in several images from diverse perspectives and preferably with high degree of overlap. Together with ongoing increase in computer power, SfM allowed digital stereophotogrammetry to be operative for close-range, high-resolution and non-metric overlapping digital images, and cost-effective. Applying these nearly automated strategies to digital images of the old bridge in Silves taken from the surrounding grounds, a dense point-cloud was computed providing its complete digital model allowing accurate measurements and materials visual identification, key elements for heritage digital catalogs and historical building information models.