International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. XXXVIII, Part 5 Commission V Symposium, Newcastle upon Tyne, UK. 2010 39 TERRESTRIAL LASER SCANNING AND NON PARAMETRIC METHODS IN MASONRY ARCHES INSPECTION P. Arias, B. Riveiro *, J. Armesto, M. Solla Dep. Natural Resources Engineering and Environmental Engineering, University of Vigo, Campus Universitario As Lagoas –Marcosende s/n 36200 Vigo Spain – (parias, belenriveiro, julia, merchisolla)@uvigo.es KEY WORDS: Arch Bridges, Laser Scanning, mesh processing, non parametric methods. ABSTRACT: Historical bridges are not only elements of our cultural heritage but also civil engineering structures. They are usually researched with destructive technologies, but their geometry is being more and more used in order to perform structural analysis, and this way it would be possible to make a diagnosis of their state of conservation. Laser scanners collect a great amount of data that allows building accurate 3D models that can be then used to make dimensional and structural analysis of these civil structures. This paper presents a geometrical research carried out in the Roman Bridge of Segura (Spain). A 3D model of the bridge was built by means of a terrestrial laser scanner, and then its geometry was analyzed by two different methods. Firstly, by means of a direct way, a graphical analysis in CAD systems was performed and the main geometrical parameters were obtained and evaluated; secondly, using statistical nonparametric methods, developed for this kind of structures, it was possible to identify pathologies on the structure thanks to the measurement of deformations in vaults by means of a symmetrical study. The results of both methods are presented in this work, and then they are compared and discussed. * Corresponding author: Tel.: +34 986 813499; E-mail address: belenriveiro@uvigo.es (B. Riveiro). 1. INTRODUCTION Historical Bridges are consolidated as key elements in order to facilitate the population movements and also the economical and cultural development of countries. This fact is present since the Roman period by means of the construction of Roman pathways where bridges played an important role as join elements. For that reason, they are the artefact designed by the engineering science in order to solve the obstacles existing in the Nature, having an important role as communication and transportation infrastructures. The constructive typology in the beginning of time was the masonry arch bridge. This way it was being consolidated as heritage legacy of the origin of the engineering discipline, with a special value in the ancient world and in particular in Europe and Spain. Historical bridges normally have some vulnerabilities that require a special attention. The presence of heavy traffic, direct exposure to floods, seismic movements and also the possible defects in the construction of the bridge make that the civil engineering should pay attention in this kind of infrastructures. Thanks to the implication of several world organizations for the preservation and conservation of the cultural and historical heritage (UNESCO or ICOMOS, 2001) non destructive methodologies have been promoted for the documentation of historical monuments and also for the evaluation of their state of conservation. Masonry bridges are civil engineering constructions that usually have a complex geometry. This complexity makes the application of the measurement devices traditionally used in heritage documentation not feasible. Building peculiarities, location, structural behavior, etc., are factors that make feasible the employment of new image based techniques, which also allow the documentation of this kind of constructions without direct contact. Unfortunately, many technicians currently involved in heritage conservation still work on the documentation of monuments in a rather traditional way. However, in the last years close range photogrammetry and laser scanning techniques have been applied to bridges inspection works, as well as other architectural and archaeological tasks. Some examples can be found in Arias et al. (2007); Jauregui et al. (2005) and Riveiro et al. (2008). The collection of 3D coordinates of millions of points over an object surface in few minutes represents a powerful tool to survey civil engineering structures, where the geometric precision and photorealistic details are also essentials. In the last years this technology has been proved in engineering structures, where measurement and monitoring of deformations are usually ejected (Zogg and Ingensand, 2008; Lovas et al., 2008, and Qiu and Wu, 2008). All the results reinforce the validity of the laser scanning technology as a useful tool in civil engineering structures. Furthermore, the “time of flight” (TOF) laser scanner offers the possibility of obtaining the radiometric information of the point clouds, making them to be optimal to survey heritage elements. In addition to this, the integration of 3D models created from laser data with Ground Penetrating Radar offers interesting tools in bridges analysis (Solla et al., 2009). Definitely, it is a fact that historical bridges should be researched by means of reliable methods; also, taking into account that in arch bridges the structural stability is, in essence, a function of their geometrical shape (Guastavino, 2006). Consequently, changes in the geometry comparing to the