ing a 
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ument 
[er 
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es not 
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ages. 
nitors; 
arizing 
at 90° 
ned a 
tically 
to the 
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arrive 
pair of 
in the 
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a good 
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ion are 
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]ternate 
cteristic 
is very important considering that an operator is 
working for many hours at the stereoplotter. 
e The image resolution is fully exploited: in 
fact it is not necessary to present the images in 
an interlaced mode. 
2.3 Stereodigit architecture 
The structure of Stereodigit is in principle very 
similar to that of an analytical stereoplotter. 
The devices for moving the frames are in this 
case substituted by two image processors 
(practically two PC), each one with its own 
magnetic storage, the relevant basic software 
and a graphic board for driving the monitors. 
The two units are linked together allowing 
therefore the exchange of the data in real time 
(position of the floating mark); one of them, 
(named master) is connected with an host 
computer which has the task of data collection 
and editing. 
The two units are connected together and with 
the host computer in a local area network for 
the download of the images forming the 
stereopair. 
2.4 Microdigit 
The design of Stereodigit has allowed to 
  
Figure 4 
Siscam the manufacture of a portable version of 
the instrument named Microdigit (see Fig. 4). 
This instrument is using two 10" liquid crystal 
displays and two portable computers installed 
in a compact supporting structure. Siscam has 
to obtain a light instrument (less than 20 Kg) 
and a reduced shape (around 0.5 cm meter), 
43 
powered also by battery, with the same 
characteristic of productivity of the Stereodigit. 
Microdigit can therefore be used directly on the 
field. Joint to a digital camera allows of testing 
stereoscopically the quality of the images 
immediately after they have been done. 
2.5 The use 
As we said, Stereodigit and Microdigit have all 
the functions of an analytical stereoplotter; in 
addition they have a set of possibilities that can 
be found only in the most sophisticated 
instruments: 
e Zoom in and out practically unlimited 
e Floating mark with shape, colour, and 
dimension selectable by the operator. 
e 3-D superimposition 
e Radiometric correction of the images 
e Negative images can be transformed in 
positive ones and vice versa 
e Automatic stereocollimation by means of 
images correlation 
A set of function, typical of a digital system, can 
be joined to the above mentioned: 
e Possibility to use the instrument as a 
"stereoscopic terminal" of a geographic 
information system if in the data bank were 
loaded the "oriented stereopairs". 
e A block of oriented stereopairs can be treated 
as a single object for 3-D measurements and 
stereoscopic investigations: it can replace a 
traditional map or orthoimage. 
e Fast updating of an existing map. 
e Inquiry system for cadastrial purposes. 
3. Digital images 
Input data to the system are exclusively (if we 
don't consider the control points coordinates 
and pre-existing vector data) digital images to 
be used for the stereorestitution operations; 
such images are in many cases stored in files of 
considerable dimension specially when aerial 
photos are used. Therefore is very important the 
connection of the digital stereoplotter in a local 
area network for data exchange. 
Moreover, if we think that a digital 
stereoplotter has not mechanical devices 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996