-52- 
A NEW SOFTWARE FOR THE AUTOMATIC REGISTRATION OF 
3D DIGITAL MODELS ACQUIRED USING LASER SCANNER DEVICES 
Leandro Bornaz (*), Andrea Lingua (*), Fulvio Rinaudo (*) 
(*) Politecnico di Torino - Dipartimento di Georisorse e Territorio 
C.so Duca degli Abruzzi, 24- 10129 TORINO 
Tel. +39.011.564.7659 / 7659 / 7700 Fax. +39.011.564.7699 
E-mail: bomaz@polito.it ; lingua@polito.it ; rinaudo@polito.it ; 
KEY WORDS: LIDAR, Registration, Close Range, Architecture, Software 
ABSTRACT: 
Laser scanner devices that allow the reconstruction of complete and dense 3D digital models, have recently been introduced into 
archaeological and architectural surveying methods. These 3D models are produced by means of the registration of many simple 
models that have been directly acquired with laser devices. 
This problem can be solved using the original, fully automatic software that has been implemented by the authors. The software 
locates pre-signalised points using reflecting markers and recognizes common points from two adjacent scans. The obtained points 
are used for the estimation of the registration parameters. 
The software also performs error filtering from the acquired raw data using robust statistical tools and, finally, the exportation of the 
obtained digital model using widespread file formats, e.g. DXF and VRML. 
This paper describes the implemented algorithms and the automation that can be obtained with the software LSR (Laser Scanner 
Registration) that has been developed by Politecnico di Torino research group. 
This software package, which is able to create an accurate 3D model in a fully automatic way, is described in this paper. The 
procedures are demonstrated by means of a practical example: the 
Martin, in the Aosta Valley (Italy). 
1. INTRODUCTION 
Terrestrial laser scanner devices today represent one of the most 
widely investigated instruments in the field of architectural and 
archaeological surveying applications. 
The main topics of the research activities can be summarized as: 
quality of the primary data, registration and geo-referencing of 
multiple scans, integration with other survey techniques (e.g. 
photogrammetry). 
In order to allow a correct and wide diffusion of this 
instruments, all these problems must be solved considering the 
particular fields of application that require cheap and easy-to- 
manage solutions. 
The quality data of the laser scanner devices can be split into 
two: metric accuracy and practical usability of the data. As far 
as metric quality is concerned, laser scanner data always 
confirm the standard deviation declared by the instruments; in 
the past many tests confirmed this fact. The quality related to 
the practical usability of the data can be defined as the 
possibility of the acquired points of correctly describing the 
surveyed object and allowing easy management by the final 
user (e.g. profile production). The complete description of the 
shape is strictly related to the density of the acquired points: 
only high densities allow the identification of the break-lines 
but, on the other hand, high densities produce enormous 
amounts of data and, as a consequence, a great deal of problems 
in the management of the data themselves. 
The registration and geo-referencing of multiple scans has been 
the most investigated topic so far. A great deal of interactive 
solutions have been proposed by different research groups and 
possible automation of the procedures has been investigated 
following the procrustes analysis approach or using high 
reflecting marks. 
Some simple integrations of laser scanning with 
photogrammetry (e.g. true orthophoto and 3D realistic 
modelling) have been tested in recent years, but further 
creation of a 3D digital model of the roman bridge of Pont Saint 
integrations should be performed to achieve new ways of 
representing architectural objects (e.g. direct and automatic 
orientation of images, automatic feature extraction, etc.). 
A new approach for the registration of multiple scans and for 
the improvement of the quality of laser scanner data, based on 
the use of reflecting targets, is here presented. 
2. DATA REGISTRATION 
A laser scanner can be considered as a motorised total station 
that is able to acquire thousands of points in a few seconds. 
When the laser scanner operates, the surveyed points are 
referenced to an internal coordinate system (see fig. 1). 
Figure 1. Internal reference system of a laser scanner 
When the object has a complex shape or when a single scan 
cannot record the entire object, a series of scans must be 
performed. In this case each scan has is own reference system 
(see fig. 2): the reconstruction of the 3D model of the surveyed 
object requires the registration of the scans in a single local 
reference system. 
This phase can be performed in an interactive environment 
through the identification of the homologous points (e.g. 
comers) in adjacent and overlapping scans. Once the points (at 
least three) are collected, a simple 6 parameter transformation