sampling can 
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constancy of 
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5 geometric 
the sampling 
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ved the most 
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els, equal to 
mined, as in 
ution in the 
Direct image 
sary become 
ner before 
e images, in 
of inherent 
geometric nature in the instrument of 
acquisition. 
The unity of acquisition has resulted therefore 
composed from a scanner DTP, from a grid for 
the scanner calibration and from a software for 
the determination of the calibration parameters 
and for the following resembling of the 
images. 
For the evaluation of the characteristics of 
geometric stability in the acquisition we have 
used a grid reproduced on a proper support to 
be acquired by the scanner (for instance on 
crushproof polyester). 
The sweaters of the used grid are characterised 
from a regular step of 2 cm in both the 
directions while the lines that materialise the 
points have a thickness of 0.1 mm. 
The software used for the correction of the 
radiometric and geometric distortions induced 
by the scanner, has been Stereoscan, a special 
form of the Stereoview software. 
The methodology of resolution of the 
orientations has been the classical one and it 
has allowed therefore a homogeneous 
comparison with the residues obtained in the 
analytical system. 
Also methodology used for the construction 
of graphic entities is absolutely similar 
between the two systems, in this way, the 
differences in the graphic product are 
imputable entirely to the quality of the 
stereoscopic coincidence and to the different 
resolution of the images. 
The analytical part of this test has been 
conducted using an analytical plotting OMI 
AP5, that has allowed, for its own 
characteristics, an attainment of an accuracy of 
2-3 microns. 
The difference between the measures 
furnished by Stereoview and those furnished 
by the analytical plotting, expressed in terms 
of coordinates of points has been used to 
esteem the precision of the digital plotting. 
For the photogrammetric plotting, either 
analytical that digital, we have used ten points 
for the relative orientation and six points for 
the absolute orientation. 
The coordinates of the support points have 
been obtained through a GPS survey network. 
The following table shows the values of the 
residues of the absolute orientation in the case 
of the analytical plotting and in that digital. 
Point 
Dx (m) 
Dy (m) 
Dz (m) 
1 
-0.034 
0.036 
-0.091 
2 
-0.078 
-0.089 
0.100 
3 
-0.019 
0.021 
0.012 
4 
0.083 
-0.061 
-0.052 
5 
-0.077 
0.081 
-0.044 
6 
-0.031 
-0.164 
0.075 
Tab.l - Residual of absolute orientation; Analytical 
plotting. 
Point 
Dx (m) 
Dy(m) 
Dz (m) 
1 
0.182 
0.161 
-0.121 
2 
-0.196 
-0.269 
0.051 
3 
-0.061 
0.318 
-0.043 
4 
-0.126 
-0.083 
-0.043 
5 
-0.226 
-0.173 
0.172 
6 
-0.139 
-0.023 
-0.101 
Tab.2 - Residual of absolute orientation; Digital 
plotting. 
The plotting operations, both analytical and 
digital, have been made by the same operator; 
he has plotted some objects by analytical 
instrument and by digital one, making two 
DXF files; then we have superimposed the two 
files so that to appraise possible removals. The 
picture n. 1 shows this particular situation. 
Fig. 1 : Superimposing of two DXF files. 
After having selected some significant points, 
we have calculated the comparison in terms of 
measured coordinates of vertexes of buildings. 
The next table n. 3 reassumes the obtained 
values. 
141