Proceedings of the CIPA WG 6 International Workshop on Scanning for Cultural Heritage Recording

Böhler, Wolfgang

Bibliographic data

Monograph

Persistent identifier:: 830281592

Title:: Proceedings of the CIPA WG 6 International Workshop on Scanning for Cultural Heritage Recording

Sub title:: September, 1 - 2, 2002, Corfu, Greece

Scope:: 159 Seiten

Year of publication:: 2002

Place of publication:: Thessaloniki

Publisher of the original:: Publ. ZITI

Identifier (digital):: 830281592

Illustration:: Illustrationen

Signature of the source:: T 15 B 1303

Language:: English

Additional Notes:: Literaturangaben

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: Böhler, Wolfgang

Corporations:: International Workshop on Scanning for Cultural Heritage Recording, 2002, Kerkira; ICOMOS/ISPRS Committee for Documentation of Cultural Heritage

Adapter:: International Workshop on Scanning for Cultural Heritage Recording, 2002, Kerkira; ICOMOS/ISPRS Committee for Documentation of Cultural Heritage

Founder of work:: International Workshop on Scanning for Cultural Heritage Recording, 2002, Kerkira; ICOMOS/ISPRS Committee for Documentation of Cultural Heritage

Other corporate:: International Workshop on Scanning for Cultural Heritage Recording, 2002, Kerkira; ICOMOS/ISPRS Committee for Documentation of Cultural Heritage

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2015

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: 5. PROJECTS AND EXPERIENCES

Document type:: Monograph

Structure type:: Chapter

Chapter

Title:: THEALASERMETRY: A HYBRID APPROACH TO DOCUMENTATION OF SITES AND ARTEFACTS. Claude E. Borg and Joseph A. Cannataci

Document type:: Monograph

Structure type:: Chapter

-27- CYRAX™ 2500 LASER SCANNER AND G.P.S. OPERATIONAL FLEXIBILITY: FROM DETAILED CLOSE RANGE SURVEYING, TO URBAN SCALE SURVEYING Balzani M. (*), Pellegrinelli A.(**), Perfetti N.(**), Russo P.(**), Uccelli F.(*), Traili S.(*) (*) Department of Architecture - University of Ferrara - Via Quartieri, 8-44100 Ferrara - Italy E.mail: balzanim@tin.it (**) Department of Engineering - University of Ferrara - V.le Saragat, 1 - 44100 Ferrara - Italy E.mail: apellegrinelli@ing.unife.it KEY WORDS: Accuracy, Laser scanning, GPS, Surveying, Cultural Heritage, Cartography ABSTRACT: The performance of the latest terrestrial laser scanners allows an expanded range of uses of these instruments. Even for laser scanners intended for architectural surveying, the maximum operational ranges reach, or in some cases exceed, 100-150 m. With such ranges, it is possible to utilize the instruments not only for measurements of single architectural elements but also for urban surveying of entire blocks or districts. This has raised the need to define a precise and reliable method to exploit the potential of these scanners. In this paper, we report the preliminary results of a procedure designed to exploit both laser scanner technology and the Global Positioning System (GPS) for surveying on an urban scale. The GPS was used to determine the three-dimensional coordinates of the homologous points used to merge together the scans. Use of the GPS allowed us to record the scans even if they did not greatly overlap. Moreover, it was possible to conduct the surveying campaign with extreme elasticity; in fact, with the GPS, the scans are georeferenced automatically even if acquired at different times and the data can easily be used for cartographic or cadastral purposes. 1. INTRODUCTION In previous studies (Balzani et al. 2001; 2002), we demonstrated the potential applications of laser scanner methods in architectural surveying. The instrument used was the Cyrax™ 2400 manufactured by CYRA Technologies. Regarding the problem of recording multiple scans, we studied the applicability and quality of automatic procedures of recognition of the flat reflecting targets suggested by the manufacturer. The results can be summarized as: - automatic recognition of the flat reflecting targets was performed with good precision and repeatability when the distance from the object was no greater than 50 m and the inclination with respect to the plane of the target was between a frontal scan and a 45° angle; for scans at distances over 50 m and inclinations greater than 45°, it was not possible to rely on automatic target recognition. However, it was possible to perform manual recognition of the target centre, with more than satisfactory results; even at large distances, measurement and restitution of the object’s natural shapes were carried out with excellent precision. On the basis of the results of these tests, we decided to conduct new experiments to evaluate the potential of the laser scanner at its maximum range in order to survey large parts of a territory in the least possible time. In addition to surveying speed, one of the problems that must be resolved in an urban application is the need to record a large number of scans without a progressive decrease in precision (effect of error propagation). After some initial tests using a spherical target, we decided to use the GPS to determine the three-dimensional coordinates of a sufficient number of targets for use in the merging of the various scans. The GPS presents numerous advantages: it allows one to quickly obtain the three-dimensional coordinates of points (in the WGS84 geocentric reference system) with centimetric precision; the times of GPS surveying (performed as described later) are comparable to those of the laser scanner and, with suitable "target/GPS" adapters, it can be performed contemporaneously; surveying of a territory (even a very large one) can be carried out in different sessions, spaced in time, all without the need to create and measure a reference network; using a master GPS station of known coordinates, the survey is framed within the WGS84 system and thus, after the appropriate coordinate transformations, can easily be used for cartographic and cadastral purposes. In the following sections, we describe the proposed methodology and report the results of our preliminary tests. 2. INSTRUMENTATION The scanner is composed of an impulse EDM and various optical-mechanical apparatuses (rotating mirrors, servomechanisms, etc.). The EDM measures the time each laser impulse takes to go from the source to the measured object and then return to the point of emission. This technology, based on the “flight time” (or LIDAR), can be used with any refracting surface. The laser impulse is guided by small rotating mirrors regulated by servomotors: in this way, a “laser paint” is activated which moves over the object to be measured. The scan appears as a consecutive series of columns of sequential points that quickly form a three-dimensional image. The accuracy of positioning of single points in space depends on the accuracies of the distance measurements and the angular measurements of the small rotating mirrors. The polar coordinate can be easily transformed in 3D Cartesian coordinate in a local frame For a detailed description of the instrumentation, see the bibliographical references. In the time between our previous studies and the present one, the Cyrax™ 2400 laser scanner was replaced by the Cyrax™ 2500 model, available in Europe in early 2002. The instrument’s software and preliminary data analysis also changed; the new software is called Cyclone 3.2 and replaces the previous C.G.P. 2.1. The study is obviously strongly influenced by the characteristics of the instrumentation used: even small operational differences can render the surveying procedures very different. The main differences between the 2500 model and the previous one are: the maximum usable range increases to 230-250 m;

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