242% 
These quantities are of particular interest for geological, 
hydrological, pedological, agricultural and forestry studies 
as well as for planning work. For a long time already, aerial 
photography has been used for many of these projects, although 
most commonly only with a parallax bar as a measuring tool. 
While the parallax measured with a parallax bar can be used to 
calculate height, no allowance can be made for camera tilt so 
that accuracy is severely limited. 
4, Accuracıy of S tereocord 
In the STEREOCORD, image coordinates are measured to within 
approx. 0.03 mm (rms error). This is roughly equivalent to the 
pointing accuracy of the floating mark. However, the accuracy 
of the terrain coordinates computed from the image coordinates 
greatly depends on how allowance is made for photo tilt. It is 
known that the three - dimensional effect given by stereoscopic 
aerial photographs is obtained by the forward motion of the 
aircraft with the camera between exposures. It is only natural 
that roll, pitch and yaw movements of the aircraft along its 
path should give rise to differences in shooting direction which 
are undesirable but unavoidable (figure 3). If two photos with 
different amounts of tilt are then viewed under a stereoscope, 
the stereo model will be distorted, that is tilted and/or de- 
formed. 
AERIAL CAMERA 
Fig.3: Model deformations 
caused by camera movement 
during the flight. 
  
Swing æ produced by yaw movement could easily be compensated 
by suitable rotation of the photographs on the photocarriage. 
Also, longitudinal and transverse tilt 9 and ww could be 
corrected by tilting the photos under the stereoscope. However, 
it is much more convenient to take these photograph tilts into 
account numerically, as is the case in the STEREOCORD. 
    
   
     
  
    
  
    
   
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