Proceedings 18 th International Symposium CIPA 2001 
Potsdam (Germany), September 18 - 21, 2001 
FAST AND ACCURATE CLOSE RANGE 3D MODELLING BY LASER SCANNING SYSTEM 
Gabriele Fangi, Federica Fiori, Gianluca Gagliardini, Eva Savina Malinverni 
University of Ancona, via Brecce Bianche, 60131 Ancona, Italy 
tei. ++39-071-2204742, fax ++39-071-2204729 
fangi@unian.it malinverni@unian.it 
www.ing.unian.it/strutture/fimet/fangi 
KEYWORDS: Laser Scanning, TIN Surfaces, 3D Modelling, Meshes Alignment 
ABSTRACT 
Completeness, speed, accuracy are some aspects of the laser scanning system for the acquisition of complex structures and sites. 
Complete geometry of exposed surface is remotely captured in minutes in the form of dense, accurate “3D point clouds”, ready for 
immediate use. This technique is used for architecture, virtual reality, heritage preservation and some other engineering and civil 
applications. Laser scanning technology offers many advantages over traditional surveying and photogrammetric methods: better 
quality results, improved safety during data capture, no interference with construction and operations activities, no time consuming, 
simplicity and easiness in learning. Furthermore in many cases, it can provide significant cost saving in both capturing surface 
geometry and in generating CAD models or otherwise using the gathered data. 
We applied the laser scanner Callidus Precision System to digitise the shape of the three-dimensional small temple inside the Mole 
Vanvitelliana in Ancona to build a 3D model. It is a complicated task, made harder by the unusually large size of the data sets. We 
processed the data by several TIN methods to obtain CAD meshes and realize an efficient 3D rendered virtual object close to the 
reality. 
1. CLOSE-RANGE LASER-SCANNER TECHNOLOGY 
For more than three decades the measurements of distances by means of laser have been operational in everyday surveying. Only 
recently the advancements in computer technology enabled the automatic collection and processing of large volumes of laser range 
data. There are a lot of such systems on the market and they differ from each other (Greco, 2000). The choice depends on the 
application. The basis of this technology is a scanning laser range finder: the distance from sensor to arbitrary points on the object 
surface is calculated from the pulse travel time. 
Some laser scanners measure distances with the flight time and some others use a phase-difference method. By computing the angles 
we can only obtain the coordinates of the point in the space. 
According to this method, the continuous laser is based on the contrary on the emission of a bundle. This bundle is divided in two 
wraps: a reference bundle that immediately hits the system for the measurement of the phase; a measure bundle, that hits the object, 
comes back and arrives to the phase system measurement. By measuring the phase-difference between two wraps it is possible to go 
back to the distance of the object. 
Also, the intensity of the reflected laser pulse is often recorded, providing an indication of the reflection characteristics of the surface. 
In some systems a fourth dimension, intensity feedback, provides an extra input as to the different materials and colours of an object 
surface. 
The 3D laser scanner is also called an active remote sensing system because no additional personnel are needed to hold a range pole 
or to place targets for measuring surfaces. Combining a pulsed laser with high speed scanning optics we can get detailed and accurate 
3D models of industrial object, works of art, buildings or inaccessible structures (Lemmens, 2001). Once tuning parameters have 
been set, like horizontal and vertical range and angular steps increment, the creation of the initial point clouds of 3D data is done 
automatically, thousands of points are scanned every second. 
To efficiently use this powerful and innovative technology, it is necessary to plan the survey correctly. A complex object demands 
the acquisition of the scan data from different positions in the space and the production of several range maps. It can be too large to 
be acquired in a single step. It can happen also that all the zones are not visible from the same direction of scanning (for instance in 
case of 3D objects with great elevation). So it is important that the first phase of the scanning process is the plan of all the scans. 
Furthermore in case of objects with a complex structure, it is necessary to acquire a high number of range maps, partly overlapped, 
employed for the meshes generation. It is, moreover, advisable to add to these range maps other range maps, in order to acquire 
particular or small articulated parts of the object. Take into account that the several range maps will have then to be connected in 
order to reconstruct the total shape. Such a connection has to be carried out manually. It is advisable, to scan together, at least, three 
flat surfaces, according to the aligning procedure of several software, used as references in the orientation. 
3D laser scanning projects enable us to obtain a fine resolution for better modelling. In fact in order to create complete, accurate 
models and drawings, it is often important to capture precise edges of structures, piping flanges, etc. In addition, to achieve high 
accuracy results registering multiple scans together, it is necessary to determine accurate positions of at least three scan “targets' 
within each scan scene. These situations require a high-resolution scanner that acquires features and targets, with a small spot size 
laser beam.