The Statue of Ramses II - Integration of Digital Photogrammetry and Laser Scanning ... 
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Two different resolutions were adopted to check the instrument’s performances: a rough resolution of 0.1 gon and a finer resolution 
of 0.04 gon. 
3. ANALYSIS OF THE LASER SCANNER DATA 
The first analysis that was performed on the laser scanner data was the accuracy test of the acquired data. Before the acquisitions, 50 
reflecting markers (5 mm x 5 mm) were positioned in a regular manner on the statue: these point coordinates were surveyed by to 
pographic procedures. All the possible distances between the points were calculated and compared with those obtained from the laser 
scanner acquisitions. The computed discrepancies showed mean values close to zero and an m.s.e. of almost 7 mm (see table 1 for 
details) in both the resolutions used. 
Resolution 
[gon] 
Minimum value 
[mm] 
Maximum value 
[mm] 
Mean value 
[mm] 
M.s.e. 
[mm] 
0.04 
-6.5 
7.3 
1.3 
±6.5 
0.1 
-7.2 
8.5 
0.8 
±7.3 
Tab. 1: Statistics of the discrepancies between the known distances and the distances computed using laser scanner data 
The obtained results confirmed the good performances of the used laser scanner (the declared m.s.e. of the instruments id of ± 8 mm), 
in terms of accuracy on well reflecting points, but these results could not be extended to the whole object. A pure visualisation of ac 
quired data in fact shows a high level of noise of a point acquired on natural surfaces. This well known effect is emphasised on the 
statue of Ramsete II, due to the dark colour of the stone. 
Fig. 6: The face of Ramsete II statue: photographic image (left), 2D rendering of raw data (centre) and axonometric 
view of raw data (right) 
This kind of information obviously cannot be used. A simple procedure, that has successfully been used with aerial laser scanner 
data, was adopted to avoid this noise effect [ROGGERO, 2001]. 
The irregular grid of the acquired points is regularised: the dimension of the mesh must be selected in such a way that at least 5 origi 
nal points are contained in each mesh. The median value is computed using all the points inside the mesh. 
All the points that show distances from the median value that are greater than a value ot r (assumed to be equal to the m.s.e. of the 
instrument) are classified as outliers; all the points that show distances that are greater than a value of R (assumed to be equal 4 times 
the m.s.e. of the instrument) are classified as gross errors. Outliers and gross errors are rejected from the computation of the final 
value (the mean of the accepted points) of the Z coordinates of the regular DTM. 
in — R rh — r in in+ r m + R 
outlier mean outlier gross error 
Fig. 7: Computation of the Z-coordinates of the regular mesh