142 
A 
N=15852,709 
E=23433,157 
H=381,901 
To' 
N=15852,839 
E=23433,020 
H=381,920 
DN=0,130 
DE=-0,137 
DH=0,019 
B 
N=15858,256 
E=23444,000 
H=381,951 
B' 
N=15858,356 
E=23443,881 
H=381,942 
DN=0,100 
DE=-0,119 
DH=-0,009 
C 
N=15870,702 
E=23484,398 
H=378,721 
c 
N=15870,845 
E=23484,192 
H=378,719 
DN=0,143 
DE=-0,206 
DH=-0,002 
Tab. 3 - Differences expressed by meters between the 
coordinates of some points plotted by analytical 
instrument and by digital one. 
As it is evident, there are some differences 
between the coordinates of these points, 
caused from the errors of coincidence of the 
operator, from the greatest or smaller visibility 
of the coincided points. 
As far as it concerns the photogrammetric 
digital system, we need to develop some 
considerations about the pixel size and about 
the image resolution. 
It is well known like one of the principal need 
of the operator, is to distinguish the greatest 
possible number of details of a digital image. 
The operator is therefore more sensitive 
towards the quality of an image, that in the 
case of the Digital Photogrammetry is closely 
connected with the camera used and from the 
Fig. n. 2 - Particular of a fiducial mark with different 
zoom 
scanner used for the digitising of the images, 
that to a difference of some microns in the 
dimension of the pixels. 
During the plotting phase, the operator can use 
the zoom to better investigate the digital 
image, but this particular instrument can give 
some problems about the enlargement of the 
image like it is showed in the fig. n.2 and n.3 
During the test, we have also considered the 
possibility, offered from the STEREOVIEW 
software, to proceed to a process of automatic 
correlation of images. 
It is well known like the techniques of images 
correlation see their great fortune in the 
possibility to automates the photogrammetric 
process and more particularly the following 
phases: 
• automatic measurement of the fiducial marks 
(inner orientation); 
• automatic measurement of parallaxes and 
image point coordinates in different images 
(relative orientation); 
• automatic measurement of the elevation of 
terrestrial points for the DTM, appraising the 
parallaxes in x. 
The image correlation is obtained through the 
measure, by now almost in all the phases in 
automatic way exclusively, of the image 
coordinates of some conjugated points in at 
least two digital images. 
It sets some problems connected to the no 
complete knowledge of the general mechanism 
of the visual perception of man. 
In parallel there are a whole series of open 
practical questions which put in difficulty the 
algorithms of image correlation. 
They are schematically: 
• the weaving of the image low or repetitive; 
• the image scale not sufficient, that can bring 
to the formations of too small zones for the 
following image treatment; 
• the different conditions of light between 
adjoining frames; 
• in general, the different geometry of 
observation (shades, zones covered by 
projections for instance for perspective effect 
of the central projection). 
The algorithms of correlation that can be 
employed are substantially the next types: 
1. those based on the correlation of areas (they 
maximise the cross correlation according to 
the principle of the least squares); 
2. those based on the recognition of details; 
Some proofs have been conducted than to the 
automatic measurement of the quota of 
terrestrial points for the following formation of 
a DTM, trying to limit the intervention to an 
area of small extension. 
The purpose was essentially that to compare