Full text: XVth ISPRS Congress (Part A2)

It might be informative to have a look on the data flow in such a system. 
The information content of the data in the digital image memories can be 
effectively used by two closed loops (Fig.2). Either the image data are 
displayed stereoscopically to an operator who moves the measuring device 
and controls this movements through the first closed loop. Or the data are 
directly used for measurements by digital correlation in a second loop 
which is completely integrated in the digital system. | 
  
STEREO- VIEWING V1 SUR Pass ones ue ‘ 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
SYSTEM 
À 
LS) DIGITAL IMAGE 
| MEMORIES 
i [T d HUMAN 
: OPERATOR 
DIGITAL ANALYTICAL 
CORRELATOR PROJECTION SYSTEM 
Lj 
! : 
figs foaming. i MEASURING A 
DEVICE 
  
  
  
  
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COMPUTER-CONTROLLED 
DRAWING TABLE 
  
  
  
Fig.2 Data flow in a stereophotogrammetric system with digital 
image correlation 
Another feature of the digital concept which is not available in conven- 
tional photogrammetric systems is the possibility of using the graphical 
overlay for storage of the data already collected. Points, contour lines 
etc. measured by the operator may be superimposed on the image as one 
chooses. This allows to check what is already done and if it is done cor- 
rectly. As already mentioned by CASE (2), superposition is a prior con- 
dition for revision of previously collected data or maintenance of digi- 
tized maps, which can be transformed into the display coordinate system 
and superimposed to the stereo-model. In a subsequent step, correction 
and editing functions for revision purposes will be integrated in the pho- 
togrammetric system. 
4. Questions of Data Processing 
  
Using turnkey image processing systems for stereophotogrammetric purposes 
is coupled with one main problem: processing of the entire stereo model 
is only possible by dividing the images into small subregions. The size of 
these subregions depends on the capacity of the frame buffer of the system. 
Displaying the actual part of the image must be organized by the user's 
 
	        
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