O Observatório Astronómico da Escola Politécnica : modelos virtuais para a sua preservação

O último observatório de ensino de interesse histórico em Portugal, que data do final do século XIX, é um dos edifícios mais carismáticos dos Museus da Universidade de Lisboa. Após um século de uso intensivo, o Observatório Astronómico da Escola Politécnica necessita de obras estruturais antes de ser devolvido integralmente à fruição pública. Recentemente, um grupo de estudantes desta Universidade foi envolvido na construção de modelos 3D virtuais para recriar o edifício do Observatório e alguns objetos das suas coleções. A qualidade dos modelos potencia a sua utilização como instrumento de divulgação de uma peça relevante do património histórico-científico da Universidade de Lisboa. Este artigo descreve as várias abordagens adoptadas e compara-as entre si.The Astronomical Observatory of the Lisbon Polytechnic School is the last teaching observatory of historical interest in Portugal. Created in the late nineteenth century, it survives intact in its original design. Given its singularity in the context of scientific heritage, the quality and beauty of its architecture, as well as its privileged location in the Botanical Garden, the Observatory has the potential to become the Museum’s focal point for the promotion of astronomy and its history. After 100 years of intense use, however, the Observatory is highly degraded and needs structural restoration before it can be fully returned to public fruition. Recently, three professors of the Faculty of Sciences of the University of Lisbon decided to involve a group of students in the construction of virtual 3D models to recreate the Observatory building and collections. This article describes the methods used to produce the models and presents a comparison between them

3D LOCAL SCALE SOLAR RADIATION MODEL BASED ON URBAN LIDAR DATA

Abstract. The aim of the present study is to obtain the direct, diffuse and reflected solar energy that reaches a generic point of an urban landscape regardless of its location on a roof, on the ground or on a façade. The vertical façades embody a discontinuity in a digital elevation surface function and most models fail in the determination of solar radiation for points on façades. The presented algorithm solves the problem in an integrated way: starting with a georreferenced LIDAR data cloud covering a 400 × 400 m2 urban area resampled in a 1m × 1m mesh, applies a new shadow algorithm over roofs, terrain and façades for each time frame, applies the Kumar solar radiation model for the calculation of direct, diffuse and reflected irradiation for each 1x1m raster cell on non vertical surfaces of roof and terrain, and calculates total and mean irradiation of each 1 meter wide column of vertical façade based on the illuminated area at each time frame. The results for each time frame are integrated for the wished time period from one hour to one year, being the time steps also selectable, allowing several kinds of solar radiation and shadowing studies. GIS were used to evaluate monthly averages of solar radiation for a particular location as well as to map the photovoltaic potential of the building façades and their roofs according to determined classes of potential. </jats:p

3D LOCAL SCALE SOLAR RADIATION MODEL BASED ON URBAN LIDAR DATA

The aim of the present study is to obtain the direct, diffuse and reflected solar energy that reaches a generic point of an urban landscape regardless of its location on a roof, on the ground or on a façade. The vertical façades embody a discontinuity in a digital elevation surface function and most models fail in the determination of solar radiation for points on façades. The presented algorithm solves the problem in an integrated way: starting with a georreferenced LIDAR data cloud covering a 400 &times; 400 m2 urban area resampled in a 1m &times; 1m mesh, applies a new shadow algorithm over roofs, terrain and façades for each time frame, applies the Kumar solar radiation model for the calculation of direct, diffuse and reflected irradiation for each 1x1m raster cell on non vertical surfaces of roof and terrain, and calculates total and mean irradiation of each 1 meter wide column of vertical façade based on the illuminated area at each time frame. The results for each time frame are integrated for the wished time period from one hour to one year, being the time steps also selectable, allowing several kinds of solar radiation and shadowing studies. GIS were used to evaluate monthly averages of solar radiation for a particular location as well as to map the photovoltaic potential of the building façades and their roofs according to determined classes of potential

GEOSPATIAL MODEL FOR LARGE SCALE SEA CLIFF ROCKFALL SUSCEPTIBILITY MAPPING

Abstract. Due to their relevance to the environment and economy, coastal areas are considered national strategic segments that should be preserved. Since erosion phenomena occur intensively in those areas, it is capital to monitor them in order to identify risk zones. In addition to national and regional studies, it is also necessary to conduct local monitoring of erosion prone areas, especially those which are often frequented by people, such as beaches limited by high cliffs. Large scale vertical mapping is necessary to model their susceptibility to mass movements, in order to provide adequate prevention, protection and assistance. Recent techniques like laser scanning or aerial photogrammetry using UAVs allow the definition of the status quo of a cliff wall and its situation a few years back. But to assess the susceptibility to rock mass movements in such cliff segments, inventories of past events are of primordial importance. These inventories allow applying several statistic models to better understand susceptibility together with a set of variables of internal and external nature regarding the cliff site. We present a case study focused on the beach of Ribeira d’Ilhas (Mafra, Portugal), where a workflow of terrestrial photogrammetry for present day situation and recovery of old analogue stereoscopic pairs (1999, 2000, 2003) was implemented. A mass movement inventory (1999-2014) was compiled by multitemporal comparison followed by a detailed characterization of the cliff using a GIS software. Finally, the application of the logistic regression method allowed the definition of a susceptibility map of the cliff wall towards the occurrence of mass movements. </jats:p

Sea cliff instability susceptibility at regional scale: a statistically based assessment in the southern Algarve, Portugal

Sea cliff evolution is dominated by the occurrence of slope mass movements of different types and sizes, which are a considerable source of natural hazard, making their assessment a relevant issue in terms of human loss prevention and land use regulations. To address the assessment of the spatial component of sea cliff hazards, i.e. the susceptibility, a statistically based study was made to assess the capacity of a set of conditioning factors to express the occurrence of sea cliff failures affecting areas located along their top. <br><br> The study was based on the application of the bivariate information value and multivariate logistic regression statistical methods, using a set of predisposing factors for cliff failures, mainly related to geology (lithology, bedding dip, faults) and geomorphology (maximum and mean slope, height, aspect, plan curvature, toe protection), which were correlated with a photogrammetry-based inventory of cliff failures that occurred in a 60 yr period (1947–2007). The susceptibility models were validated against the inventory data using standard success rate and ROC curves, and provided encouraging results, indicating that the proposed approaches are effective for susceptibility assessment. The results obtained also stress the need for improvement of the predisposing factors to be used in this type of study and the need for detailed and systematic cliff failure inventories