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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;