SURVEY, REPRESENTATION AND ANALYSIS OF A WAR I COMPLEX SYSTEM OF SURFACE AND UNDERGROUND FORTIFICATIONS IN THE GRESTA VALLEY, ITALY

Abstract. This work is part of a research on the use of terrestrial laser scanner, integrated with total station and GPS, for the documentation and comprehension of complex architectures in up-land sites. The research is performed in the framework of the project "Ambiente e Paesaggi dei siti di Altura Trentini" – APSAT (Environment and landscape of hill-top sites in Trentino), a multidisciplinary project focused on the evolution of hill-top anthropic system in the Trentino region, Italy. The study area is located in the Gresta Valley and this work concerns on the Nagià Grom site, fortified by the Austria-Hungarian Army during the World War I. The site has been interested by a significant restore operation of a large series of entrenches paths and fortifications in the last decade. The survey herein described has involved an area once interested by military barracks with Officers' Mess, water provision and by one of the biggest field kitchens discovered in the Trentino region. A second survey involved the tunnel connecting the ammunition depot to the artillery stations. The nature of such complex architectures, characterized by an irregular and composite 3D span leads, in general, to necessary simple surveys and representations and somehow to simplified studies too. The 3D point cloud, once filtered by the massive presence of dense vegetation, eventually constitutes a rich data set for further analyses on the spatial, geological, architectural and historical properties of the site. The analysis has been carried out on two different scales. At the architectural-scale, the comparison to historic photos has allowed to understand how the original structure of the barracks was made and to find building characters that now are lost. The on-site observation of the underground stratigraphic splices and their analysis in the 3D point cloud, e.g., spatial extension and slope, have permitted the understanding of the special excavation process guided by the practical advantage of exploiting the natural collapse of the rock along the stratigraphic splices. At the landscape-scale: the 1918's aerial photos, showing the trenches and military barracks during the World War I, have been georeferenced and compared to recent ortho- photos and DTM to evaluate the landscape changes and to assess the complete detection of the entire set of fortified structures. The analysis involved also the evaluation of the landscape visibility from some key points of the fortification and the visibility of the same fortification from the surrounding landscape. That has permitted, for example, to underline the very strategic location of the field kitchen. The availability of the 1×1m ALS DSM suggests a possible processing for the detection of the preserved surface artefacts and trenches so to extend the metric knowledge of the fortification system and to plan further surveys.