statues) 
hotos of 
fact, it's 
) model 
2] size is 
scanning 
e with a 
1at point 
e digital 
xd. 
ie plane) 
  
survey is 
; way we 
Nc and 
used to 
ing the 
Marco in 
ic entity 
rpolating 
    
  
   
     
Figure 1 and 2 want to expalin construction of an arch based on 
n rectified points. If the distance between the points and the 
interpolated arch is less than the graphic precision (0.2 mm x 
scale of representation) the plotted entity becomes the 
circumference. 
Beading (cornices) of architraves and lintels is even more 
evident, since they are parallel to the construction of the orders 
(figure 3-4). 
  
  
Figure 3: Errors in plotting 
  
Figure 4: Correct orders plotting 
From the photogrammetric plotting, we can see that the warping 
is due to unavoidable rectification errors. We affirm that these 
errors have a normal distribution and therefore, if a cornice has 
been rectified with many points, it is more sensible to 
interpolate the points to obtain a straight line that represents it. 
Clearly this reasoning is valid in the case where there is no 
breakage due to decay phenomena. 
The laser can survey many points that are indifferent with 
respect to the architecture: they belong to the object but are not 
chosen by the operator who understands the rules of the 
architectonic composition (like architectonic orders). (Figure 5) 
The problem with survey done with laser technology is 
obtaining an architectonic representation starting with those 
points. 
atas 
iet 
ains 
Figure 5: Points cloud for the survey of the main facade of the 
Stazione Centrale in Milan 
Currently, many work groups are working on trimming down 
the points cloud, eliminating the noise to reconstruct the 
surfaces. 
The work done by the authors is mainly addressed to obtaining 
an immediate result: generation of orthophotos using the cloud 
of laser points for creating DEM and the same laser points 
appropriately chosen because of the orientation with the DLT of 
the photograms taken with digital, non-metric cameras. 
For the DEM, diverse algorithms have been tested which have 
all shown various constraints due to the complex configuration 
of the architectonic surfaces. 
In fact, unless uniform brickwork is surveyed (for which the use 
of lasers would be useless) architecture shows discontinuity due 
to the volumetry of the structure and the presence of accessories 
and ornaments. 
It is therefore particularly difficult to generate mesh 
automatically without preliminarily treating the clouds. These 
processing include identification of the subset points that 
logically belong to a compositional part of the architecture, as 
one understand when thinking about a wall, a column, a vault or 
a parapet. 
—303—