- 118 - 
via reference points (method useful for registration of 
multiple scans); 
by automated techniques relying mainly on the recognition 
of the same flat areas on contiguous scans. 
browser (fig. 10), and distances interactively and immediately 
measured between couples of points. 
The successive step is the creation of the 3D mesh and the final 
3D model, after a series of refinements that, as well known, in 
general require powerful software and hardware platforms. 
Three scans were realised for the Big Fountain with 80 mgon 
resolution, one central (4 frames averaged) and two laterals, and 
only a central scan acquisition for the Small Fountain. 
In order to better compare the results of the photogrammetric 
and laserscanning process, the same targets, whose coordinates 
were determined by a topographical survey, were used for the 
exterior orientation in both the two approaches. 
Figure 8 shows the phase of automatic localisation of the 
targets, based on their high intensity values, realized by 3D 
RiVIEW Riegl software for the nympheum of the “Flouse of the 
Big Fountain”; the coordinates of the targets were supplied as a 
separate file. The automatic localisation, and the subsequent use 
for stitching together different scans, was successfully tested 
using the program Laser Scanner Registration 1.0 (Bomaz et al., 
2002); the results, after a decimation of the cloud points, are 
shown in figure 9. 
Fig. 8 - House of the Small Fountain: registering the scans by 
automatic identification and association of control 
points. 
Fig. 9 - House of the Big Fountain, after automatic registration 
of three scans and subsequent point decimation. 
The free visualisation software provided by the Riegl firm (or 
other programs) permits this combined cloud of points to be 
exported in .wrl format and easily explored by a VRML 
Fig. 10 - House of the Big Fountain, interactive exploration of 
the three co-registered point clouds by a VRML plug-in 
in a standard browser. 
3. COMPARISON AND INTEGRATION 
OF THE TWO TECHNIQUES 
During these experimentations, some preliminary tests were 
realized in order to verify the accuracy gained by different 
techniques. 
Considering for instance about 40 differences in distance 
between couples of control points in respect to the values 
derived from the topographical survey we have: 
Table 1 - Accuracy test: differences for absolute distances in 
respect to values obtained by total station surveying 
(values in meters). 
mean 
min 
max 
st. dev. 
Photogrammetry 
(ROR+AOR) 
0.002 
-0.012 
0.012 
0.008 
Photogrammetry (scaled 
model coordinates) 
-0.002 
-0.021 
0.011 
0.010 
Laser scanning 
(instrumental coord, 
system) 
0.004 
-0.020 
0.022 
0.010 
Taking in account the above mentioned limitations of this 
model of laser scanning for short distances and other 
experiences in literature, it appears that the accuracy provided 
by laser scanning systems is today well comparable with 
photogrammetry, and for some systems is better. 
Some general considerations deriving from our experience can 
be briefly expressed. 
The advantages of laser scanning, some of these in common 
also with photogrammetry, with respect to traditional surveying 
methods for archaeological sites and structures, and in general 
for cultural heritage preservation and documentation, could be 
briefly summarized as: 
short data acquisition time; 
very accurate 3D models obtainable from high density point 
clouds;