lack, to an increasing extent, point density with increasing distance 
from the format center. Stellar calibrations provide a high point 
density and good uniformity in point distribution but fail to provide 
information in the format corners (Point distributions F and G). 
This is not caused by a lack of suitable object points but rather by 
the reduction in resolving power of the lenses. 
The different point distributions affect different weighting in 
the determination of the parameters of the interior orientation 
because of their influence on the optimization of the average radial 
lens distortion. It is for this reason that it is planned to compare 
all results after they have been used to determine the lens distortion (0 
values for each point of the camera reseau, that is, for the point 
distributions H shown in Figure 8. The interpolation of the values 
for the reseau points will be carried out in stages: firstly, the 
radial symmetrical component of the lens distortion will be 
determined; secondly, the decentered lens distortion will be 
determined from the residual lens distortion remaining after the 
subtraction of :he radial symmetrical distortion;  thirdly, the 
residual lens distortion remaining after the subtraction of both, 
the radial symmetrical and the decentering components, will be 
transferred from the original data points to the reseau points by least 
square interpolation; and finally the decentered lens and the radial 
symmetrical distortion components will be added at each reseau point. 
Once the lens distortion is known for all reseau points, the 
calibrated focal length will be modified by applying the same 
weighting function to all the different lev: distortion determinations 
in the form of a spatial resection. 
At present, the calibrated focal lengths vary somewhat. These 
variations are to some extent the result of either accuracy limitations «9 
or small actual changes as indicated by the results of calibrations 1b, 
4b and 8b, which were all carried out at the National Research Council 
using the same procedure. Processing of the goniometer data 
provided by the two manufacturers (calibration 2a) and Hakkarainen 
(calibration 3a) in the same way as for calibrations lb, 4b and 8b 
resulted in very similar calibrated focal lengths (calibrations 2b 
and 3b). Calibrations la, 4a, 5, 7 and 8a were carried out with the 
image plane rather than the reseau plane as reference; all give 
similar calibrated focal lengths. The cause of the deviation of 
the calibrated focal length for calibration 6 from the mean of all 
other calibrations has not yet been determined. This deviation is 
particularly pronounced for the RC8 camera; a glance at the 
—16-