TERRESTRIAL LASER SCANNER DATA PROCESSING 
L. Bornaz (*), F. Rinaudo (*) 
(*) Politecnico di Torino - Dipartimento di Georisorse e Territorio 
C.so Duca degli Abruzzi, 24 — 10129 Torino 
Tel. +39.011.564.7687 / 7659 Fax. +39.011.564.7699 
Email: leandro.bornaz@polito.it; fulvio.rinaudo@polito.it 
Commission V, WG V/4 
KEY WORDS: Cultural Heritage, Surveying, Analysis, Registration, Laser scanning, Software. 
ABSTRACT: 
The introduction of new terrestrial laser scanner devices in the survey field has increased the possibility of more accurate and 
complete 3D models of the acquired objects to be obtained. This happens, above all, in the architectural and archaeological survey 
field in which the shape of an object is usually remarkably complex. Acquisition with laser scanner devices is, in addition, very fast 
and cheap and the 3D models that are obtained are very useful for users. However, particular attention must be paid during the 
analysis, the processing and the modelling phases of the laser scanner data. 
The acquired data are often characterized by the presence of elevated noise (usually gross errors and outliers) which must be removed 
with ad hoc techniques before starting with the manipulation of the data. 
Usually architectural and archaeological objects have a very complex shape and one scan is not enough to obtain the complete 
description of the object. In these cases, in order to eliminate the shaded areas, two or more scans must be taken from different points 
of view of the same object. To obtain the final 3D model of the object it is therefore necessary to align and to georefer the single 
scans using suitable registration techniques. 
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In addition, when it is necessary to align a large series of scans, the use of triangulation algorithms represents the only way to avoid 
distortions of the 3D model, in complete analogy with the case of long single strips in photogrammetry. 
All these aspects have been considered and a specific software that is able to correctly process terrestrial laser scanner data has been 
developed by the authors. The paper presents the algorithms and the solutions adopted in order to prepare the laser scanner data to the 
subsequent work phases. 
1. LASER SCANNERS 
1.1 Terrestrial laser scanners 
Recently new instruments have been introduced in the field 
of surveying that are able to acquire portions of land and 
objects of various shapes and sizes in a quick and cheap way. 
These instruments, based on laser technology, are commonly 
known as terrestrial laser scanners. 
While laser scanner instruments based on the triangulation 
principle and high degrees of precision (less than | mm) have 
been widely used since ‘80s, the TOF (Time Of Flight) 
instruments have been developed for metric survey 
applications only in the last 5 years. 
These type of laser scanners can be considered as highly 
automated total stations. They are usually made up of a laser, 
that has been optimised for high speed surveying, and of a set 
of mechanisms that allows the laser beam to be directed in 
space in a range that varies according to the instrument that is 
being used. 
For each acquired points a distance is measured on a known 
direction: X, Y and Z coordinates of a point can be computed 
for each recorded distance-direction 
Laser scanners allow millions of points to be recorded in a 
few minutes.. 
Because of their practicality and versatility, these kinds of 
instruments are today widely used in the field of 
architectural, archaeological and environmental surveying. 
2. THE TREATMENT OF LASER SCANNER DATA 
2.1 Laser scanner data 
As mentioned before terrestrial laser scanners can be 
considered as highly automatic motorised total stations. 
Unlike total stations however, where the operator directly 
chooses the points to be surveyed, laser scanners randomly 
acquire a dense set of points. The operator only selects the 
portion of the object he wishes to acquire and the density of 
the points he desires in the scan (usually the angular step of 
the scan in vertical and horizontal planes can be selected by 
the operator). Once these initial values have been choosen, 
the acquisition is completely automatic. 
The result of the laser survey is a very dense points cloud 
(also called DDSM — Dense Digital Surface Model). For each 
point of the model the X, Y, and Z coordinates and the 
reflectivity value are known. 
As this set of points is acquired in a completely arbitrary 
way, with the exception of the parameters imposed by the 
operator, it is necessary to manage this data in a critical and 
reasonable way. Particular attention must be paid to the 
quality of the original data. 
2.2 Laser scanner data treatment 
The laser scanner data treatment consists of a set of actions 
that are necessary to obtain the correct digital model of the 
    
   
   
    
   
   
     
  
  
  
  
  
  
  
  
     
    
   
  
    
    
   
   
   
   
    
   
    
    
   
    
   
   
   
     
   
    
   
   
    
   
   
    
   
        
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