(Salamanca, Spain) by Terrestrial Laser Scanner Intensity Data
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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XL-5/W4, 2015 3D Virtual Reconstruction and Visualization of Complex Architectures, 25-27 February 2015, Avila, Spain ASSESSING PATHOLOGIES ON VILLAMAYOR STONE (SALAMANCA, SPAIN) BY TERRESTRIAL LASER SCANNER INTENSITY DATA J. García-Talegóna,*, S. Calabrésb, J. Fernández-Lozanoa, A.C. Iñigoc; H. Herrero-Fernándezc, B. Arias-Pérezb, D. González-Aguilerab a Department of Geology; Faculty of Sciences, University of Salamanca, Salamanca, Spain – ([email protected], [email protected]) b Department of Cartographic and Land Engineering; High School of Ávila, University of Salamanca, Ávila, Spain – ([email protected], [email protected], [email protected]) c Spanish National Research Council, Instituto de Recursos Naturales y Agrobiología de Salamanca, Salamanca (CSIC) ([email protected], quinto_ciceró[email protected]) * Corresponding author Commission V, WG V/4 KEY WORDS: Pathologies, Cultural Heritage, Villamayor Stone, Terrestrial laser scanner, Photogrammetry, Single-lens reflex camera, Remote sensing, Supervised classification. ABSTRACT: This paper deals with the assessing of pathologies in façades using a variety of intensity data provided by different terrestrial laser scanner. In particular, a complex building built in the Villamayor Stone that is to be candidate as a Global Heritage Stone Resource has been chosen as study case. The Villamayor Stone were quarrying for the construction and ornamentation of monuments in Salamanca, declared World Heritage City by UNESCO in 1988. The objective of this paper is to assess the pathologies of Villamayor Stone and compare the results obtained through the laser techniques with the classical techniques of mapped pathologies (i.e. visual inspection). For that intensity data coming from laser scanners will be used as non-destructive techniques applied to the façades and several retired plaques (after of building restoration) of Villamayor Stone with pathologies (fissures, scales, loss of matter, humidity/biological colonization) carried to the laboratory. Subsequently it will perform different comparisons between the accuracy reached with the different sensors and a high precision model setup on laboratory which performs as “ground truth”. In particular, the following objectives will be pursued: i) accuracy assessment of the results obtained in in situ and laboratory; ii) an automation or semi-automation of the detection of pathologies in Villamayor Stone; iii) discriminate the different types of Villamayor Stone used in the façades in function of the radiometric response; iv) establish a methodology for detection and assessing of pathologies based on laser scanner intensity data applied to monuments and modern buildings built in Villamayor Stone. 1. INTRODUCTION particular, terrestrial laser scanners have gained popularity in the last decade related to the tasks involving geometric The conservation of cultural heritage is one of the fundamental characterization. The terrestrial laser scanner provides a great concerns and potential of modern society and particularly, volume of information quickly and with high accuracy. The historic infrastructures largely characterize modern Europe. information is formed, at least, by a point cloud with spatial Historical constructions present a cultural legacy that needs to coordinates of the points and metric capabilities. In addition, be preserved. This generic term includes a wide range of the main advantage of this technology is their non-destructive constructions such as residential buildings, religious buildings, nature (Genovese, 2005), together with the crosscutting or even civil structures such as bridges. Many of these applications of the technologies to many different fields: constructions are still in service, which is a proof of their archaeology (Lamberts et al., 2007), civil engineering historic and engineering value, so their preservation must be a (Lubowiecka, et al., 2009; González-Aguilera et al., 2008), vital concern of modern and advanced reflective societies. geology (Buckley et al., 2008) and geomorphological analysis However, when these constructions need to be evaluated from (Armesto et al., 2009), among others. Thus, this technology the point of view of engineering, many restrictions make it represents a very attractive and powerful tool for the study of difficult to obtain accurate and realistic analyses. Among others, historical constructions, but they still need to be explored the main aspects that characterize the engineering evaluation of further. In fact, radiometric information, provided by the historical constructions are: intensity measurements in the case of laser technology, is used • Complex and often unique geometry. less frequently, so that its potential for classification tasks and • The uncertainty and diversity of the mechanical properties of recognition of different materials should be investigated. the materials, and construction technologies. Recently radiometric information has started to use in the • Unknown techniques and processes during the staged detection of different pathologies in granites (González-Jorge et construction. al., 2012) and detection of humidity and lichens in granite • Vulnerability and monumental status of the construction. (Rodriguez-Gonzálvez et al., 2013). Although, nowadays several works have been performed in granites and other Close-range remote sensing has evolved importantly in the last materials, never an exhaustive study has been realized over the decades in terrestrial environments: new technologies such as Villamayor Stone. laser scanning have significantly contributed to this growth. In This contribution has been peer-reviewed. doi:10.5194/isprsarchives-XL-5-W4-445-2015 445 The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XL-5/W4, 2015 3D Virtual Reconstruction and Visualization of Complex Architectures, 25-27 February 2015, Avila, Spain The objective of this paper is to assess the pathologies of 2.2 Villamayor Stone: Pathologies Villamayor Stone and compare the results obtained with the intensity data coming from laser scanners with the classical Looking at the Villamayor stone monuments it can be deduced techniques of mapped pathologies (i.e. visual inspection). For that on the façades exposed to the sun and the joint action of that it will be used several kind of laser scanners applied to the wind and rain (Rives and Vicente, 1993), but without the façades of a complex building “El Tormes” located in constant humidity to produce their arenization, the patina is Salamanca (Spain) and to several retired plaques (after of more intense. Two types of surface modification of the building restoration) of Villamayor Stone with pathologies. Villamayor Stone in these monumental microenvironments have been defined: i) on vertical surfaces which have good drainage The paper has been structured as follows: after this and are exposed to the sun, good conservation of the stone can introduction, Section 2 presents the Villamayor Stone as a be observed and it acquires a beautiful golden patina and ii) if Global Heritage Stone and its pathologies. Section 3 outlines in the stone is located in zones of frequent humidity, water with or details the methods developed; and the final two sections without salts (nitrates, chlorides , sulfates, phosphates, etc.) summarize the experimental results and present conclusions which is located in the lower parts of the monument rises from drawn from the study. their bases by capillary action. The patina is a symptom of the condition of the stone, and contributes to its conservation (Vicente and Brufau, 1986). 2. MATERIALS During the years 2007/2008, detailed mapping pathologies and 2.1 Villamayor Stone: Heritage Stone different varieties of Villamayor Stone are preceded, due to the detachment of small portions of the façade cladding close to the In Salamanca (Spain), which was declared a World Heritage copings of the cornices and the terraces of the building (Figure City by UNESCO in 1988, the construction of the principal 1). The decay of the Villamayor Stone was consequence of the religious and civil monuments maintains a fixed pattern in the bad drainage system in the copings of the building, together join use and position of the Villamayor Stone that is used. In the to the humidity sensibility of this stone and abrupt changes of lower parts of monuments and columns (base, shaft and capital) temperature (frost weathering "ice wedge effect" by increasing other types of Heritage Stones have been used such as silicified water volume when its physical state changes) were producing a conglomerates, Sandstone Salamanca Formation (Tosca Stone); deterioration in the copings in a short time (less than 7 years). monzogranite, Granite of Los Santos; and Leucogranite with The mean decay of the Villamayor Stone is leading to tourmaline of Martinamor (Stone of Vaugnerite) (García- microfissures, scales, flakes and loss of matter (Figure 1) Talegón et al., 2014; López-Plaza et al., 2007a, b). following ICOMOS glossary (2011). Villamayor Stone is an arkosic stone of the Middle Eocene age From the climatic data of Salamanca city, it is concluded that and belongs to the Cabrerizos Sandstone Formation that the climate of Salamanca can be defined as a Mediterranean comprises braided fluvial systems and paleosoils at the top of with a continental trend, with an annual mean temperature of each stratigraphic