When the object is near flat it is enough to 
eliminate the consequences of the perspective 
effects by means of a global transformation of 
homographic type. Our ARCHIS software, an 
user friendly package in Windows environment 
(see Fig. 1), allows the production of a 
photoplane of either aerial or terrestrial photos. 
When the objects to be treated are 3-D ones, 
ORTHOMAP package, is producing 
"orthoprojection" where the heights 
displacements are corrected pixel by pixel on 
the base of a digital model of the object: the 
relatively complex operation mode is 
addressing this software mainly to the 
cartographic production. 
2. The systems for digital restitution 
2.1 Stereodigit 
A basic problem to solve in designing a system 
for digital restitution is to realize the 
stereoscopic vision; images correlation, an 
important feature in a digital stereoplotter, 
cannot be considered an alternative way to the 
human collimation: in many eases the 
automatism does not work or gives 
unsatisfactory results and is therefore required 
the supervision of the operator. 
Numerous are the methods which allow the 
  
Figure 2 
vision and the stereoscopic collimation of a 
digital stereopair: among these methods we can 
mention systems including traditional optical 
components (mirrors and lenses) for separating 
stereoscopic images. In other systems the 
stereoscopic vision is achieved electronically 
by an high frequency switching of the images 
concerning each eye. 
42 
We operate a designing choice realizing a 
stereovision with 'no alternate filtering: we get 
a more comfortable vision. This choice has 
important influence in defining the instrument 
architecture. 
2.2 Stereovision in the Stereodigit plotter 
The system we are using for getting the 
stereoscopic vision in the Stereodigit does not 
contemplate the use of optical systems inserted 
between the operator and the observed images. 
We are using two high brightness flat monitors; 
in front of which are mounted two polarizing 
filters. The two displays are mounted at 90° 
each other; on the diagonal is positioned a 
beam splitter which has the task to optically 
merge the images and transmit them to the 
observer. 
The images, filtered by the polarizing screens, 
merged by the beam splitter, arrive 
simultaneously to the operator's eyes. A pair of 
glasses with polarizing lenses oriented in the 
same way as the screens allows the separation 
of the images giving therefore a right 
  
Figure 3 
stereoscopic vision.(see Fig. 3). 
The beam splitter must be realized in a way 
which cannot alter the polarization imposed by 
the filters in front of the monitors; moreover it 
must have a low energy absorption and a good 
balance between transmitted and reflected light. 
The advantages of this kind of stereovision are 
mainly the following two ones: 
e The vision is more comfortable and 
agreeable because of the absence of flickering 
phenomena due to a dynamic alternate 
. polarization. We assume that this characteristic 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996 
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