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expressing radial symmetrical and decentered lens distortion in 
addition to the calibrated focal length, the point of best symmetry 
and, in calibration 6, the principal point of autôcollimation. All 
other calibrations provide a setup with reference to the principal 
point of autocollimation, the measurement of the distortion with 
reference to this point and an adjustment to find a point of best 
symmetry. ' 
Rather than comparing certain values, as was done in the last 
section, one can also investigate the effectiveness of the correction 
of measured image coordinates using all parameters of the interior 
orientation, for example by means of photographs over a photogrammetic 
test field. Such an investigation has been carried out at The Ohio 
State University in the course of a doctoral program by Jiwalai [15] 
under the advisorship of Prof. Dr. D.C. Merchant [16], the vice- 
chairman of the Working Group on Image Geometry, using RMK photography 
obtained for this working group over Rheidt Test Field near Bonn, 
West Germany (BRD). 
First, a single photograph with 34 uniformly distributed points 
was used. All calibrations resulted in very similar residuals and a 
2.test at the 5% level of significance did not provide evidence to 
reject the null hypothesis that all results have the same mj. 
Table 3 lists some of the results obtained, Table 4 a typical 
correlation matrix which indicates strong correlation between x. and 
and between Yo and ® . The principal point shifts resulting 
from the rotations o and o are more accurate and almost always 
smaller than the actual shifts. The largest rotations are obtained 
for calibration 2a, the only one disregarding the tangential 
distortion. The variations in Zo indicate differences in the 
calibrated focal length; it was determined for the reseau plane 
in calibrations 2a, 3a, 4b and 6, and for the image plane for 
calibrations 5 and 7. It appears that the spacing between reseau 
plane and image plane of approximately 25 um was not taken into 
account properly. The values obtained by calibration 6 and listed 
in Table 1 deviate significantly from the others. 
Second, one of the resections was repeated, now using 34 groups 
of three relatively closely spaced points instead of 34 points. The 
obtained root mean. square positional errors within the groups 
(m = * 3.3 um,m = * 2.9 um) indicate, when compared with the overall 
rms positional errors (m = 4.3 um and mi 5.0 um), that some 
uncompensated systematic error is present in the data. 
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