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The standard error of unit weight of the y-parallax measurements on the image scale showed 
a clear tendency to decrease with increasing scale factor (flying altitude). It was particularly 
interesting to find that the mean square values of the discrepancies in planimetry and elevation from 
the practical tests behaved in the same manner. 
4.3 Mirror stereoscope and parallax bar 
From numerous test measurements of elevations with the mirror stereoscope and parallax bar the 
theoretical relation between the standard error of unit weight of y-parallax measurements and the 
mean square value of elevation discrepancies has been checked. 
In reference [12] some published results could be used for the check. 
The standard error of unit weight of the y-parallax measurements was determined as 0.026 mm 
on the scale of the photographs. According to the number and location of the elevation control points 
the mean square value of the elevation discrepancies can be determined from the formula 
where $,—0.026 mm and the scale factor S— 5400. 
Hence 
M,=250 mm 
From the practical tests the corresponding value was determined as 0.3 m (0.2 m after a minor transla- 
tion of the elevation discrepancies). 
SUMMARY 
In this investigation the errors of the final results of the photogrammetric procedure (the dis- 
crepancies in the check points) are assumed to have been caused by the errors of the fundamental 
operations of the procedure. The task of Sub-commission IV:4 has been to investigate the sources of 
errors, to estimate the magnitude of the errors of the fundamental operations and to study the error 
propagation to the final results of the photogrammetric procedure. From the practical results of the 
investigations of Sub-commissions IV:1 to IV:3 checks of the theoretical accuracy expressions are 
expected to be obtained. If the theoretically derived relations prove to agree sufficiently well with 
practice, accuracy tests of the photogrammetrie procedures can be considerably simplified in the 
future. Specifications for photogrammetric map production can be founded upon the theoretical 
laws for the error propagation. 
Owing to the practical conditions of the controlled tests only the fundamental operations Nos. 2 
and 3 have been treated. The practical measurements have been performed by some participants in 
the controlled tests. 
From grid tests of instruments valuable information was obtained concerning the basic accuracy 
under different practical conditions (base zero, in and out). In particular corrections to the elements 
of orientation, radial distortion curves, standard errors of unit weight of image coordinate measure- 
ments and residual errors were determined after computations in high speed electronic computers. 
The most important results of the tests are demonstrated above, and partly also in Appendix 1. 
For the autograph A7 and the stereoplanigraph C8 the magnitude of the standard error of unit weight 
of image coordinate measurements was found to be 6 —7 microns. In these figures the possible errors 
of the grids are also included. (See 1.3.) Considerable influence upon the geometric conditions was 
found from the different base settings (zero, in and out). In plotting single models these influences 
will be partly compensated through the relative and absolute orientation. 
From y-parallax measurements the actual situation of the relative orientation of the test models 
was checked and basic statistical data for a determination of the accuracy of the relative orientation, 
26 
  
  
  
  
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