CI P A 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey 
The segmentation work was carried out on a part of the 
building which contains the Department of Georesources and 
Land of the Politecnico di Torino. The survey was performed 
using a RIEGL LNS-Z420 laser scanner. Apart from the 
façade, the laser scanner also surveyed some internal parts of 
the building and part of the external pavimentation. 
It was hoped to obtain the main plains of the object using the 
developed software: the façade, the external pavimentation 
and then the remaining parts. 
The result was positive. Only a few minutes were necessary 
to carry out the whole operation. 
From the figure it is possible to see how the objects 
belonging to different plains were in fact grouped together in 
different layers. These are visualised in the image by 
assigning different colours to them. The model can be 
exported into AutoCAD environment, assigning a different 
layer to each entity. 
3.2 Region growing and Analysis of the main components 
A scansion of the “loggetta” of Sansovina was used for the 
evaluation of the segmentation capacity of the region 
growing model and for the analysis of the main components; 
this — can be found on the lower part of the bell tower in 
Piazza San Marco in Venice. 
He survey was carried out using a RIEGL LMS-Z420 laser 
scanner. 
Figure 5 - the “loggetta” of Sansovina - Venice - Italy 
This is an interesting archaeological example as the object 
has a series of complex structures, including columns, some 
internal niches inside which there are statues and bas-reliefs. 
Two different types of elaborations were carried out. 
The software that was used for the elaboration combines 
region growing techniques with an analysis of the main 
components (Roggero, 2002). Some describers were defined 
for the segmentation (inertia moments and tensors, curvature 
and static moments). 
Limits were imposed on the curvature in order to be able to 
correctly carry out the aggregation. 
A first elaboration of the data was carried out using not very 
rigid constraints on the aggregation. This means that during 
the segmentation procedure the most evident discontinuities 
were evaluated while the small discontinuities were not 
considered. 
The results of this first elaboration are shown in figure 6 
The segmentation algorithm identified 14 main portions of 
point clouds (the columns, the statue, portions of walls etc.). 
The software that was used for the elaboration organised the 
results in an AutoCAD file according to the different layers 
that were identified. 
Figure 6 - Segmentation of - the “loggetta” of Sansovina. - 
Venice - Italy 
The elaboration was then repeated using more rigid research 
parameters. 
Using this more rigid aggregation method means looking for 
the less obvious discontinuity models. This type of 
elaboration allows the point cloud to be chosen in smaller and 
more homogeneous portions. 
This time it was possible to distinguish not only the columns 
but also the capitals on different layers. 
The presence of many layers on one hand can lead to an 
increase in the time that is necessary for the solid modelling, 
while on the other it can lead to a better sub-division of the 
model and therefore to a more complete model.