accordins to 2.1 - 2.2 can also become independently Checked, 
The relative orientation of all aerial photogrammetrig 
models should bz checked from y-parallax measurements in 
at least 9 symmetrically located points, This check is of 
similar importance in photogrammetry as is the check of the 
sum of the angle measurements in geodesy. 
The final check measurements of the y-parallaxes should 
be performed after the absolute orientation. The location 
and elevation differences of the model points where the y- 
parallaxes are measured should also be recorded. 
For more detailed tests of the photogrammetric model, 
the y-parallaxes can be measured simultaneously in more 
points. Convenient computations can be performed from y- 
paraliax measurements in 15 and 25 points. 
The residual y-parallaxes of the model can be used for 
convenient but only approximate determination of the resi- 
dual radial distortion curve and some other types of syste- 
matic errors after the reconstruction of the pencils of rays 
in the plotting instrument. 
Summary 
It seens desirable that these sugzestions be discussed 
in connection with the VIII International Congress for Photo- 
graunetry in Stockholm 1956. If the main principles are 
accepted by the Congress, detailed plans for the performance 
the tests should be worked out by a special committee. 
  
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