The effect of the intermediate control zones has already been discussed 
(Page 9, para. 3) and it has been shown that had these been omitted the result 
would not have been altered by more than about 3ft. at any point. Considering 
that the length of the APR bridges between the terminal control of the N-S 
strips varied between 36 and 82 miles, the result of this final analysis is highly 
encouraging. A total of 194 check readings were made spread over forty-one 
overlaps and nine different strips. The mean square error of all readings was 
4.2ft.. This included two extreme cases with errors of +15ft. and -16ft.; both 
points fell near the centre of overlaps containing at least six other check 
points, none of which showed an error of more than 6ft. It seems certain 
that the excessive error of the two points was due to misidentification and it 
is logical therefore to ignore these two points, in which case the mean square 
error of the remaining 192 points is reduced to 3.9ft. and the extreme errors 
are +8ft. and -10ft.. All readings were corrected for earth curvature, the 
maximum correction being 3ft.. 
The distribution and frequency of these absolute errors is shown in 
Diagram C to be evenly divided between positive and negative values. It is also 
to be noted that 8096 of all check points lie within 5ft. of their true value. 
The following facts about the survey are worth emphasis:- 
1) The APR control flying along the lateral overlaps of the survey 
photography was completed in five flying days out of a total of 18 
spent on the whole operation. 
2) The ground levelling for controlling the APR profiles took 38 man- 
weeks compared with the estimate of 170 man-weeks required to 
provide normal height control for photogrammetric mapping. 
3) The contoured maps of the whole reservoir area were delivered 
within three months of completion of photography and APR flying 
and one month ahead of schedule. 
4) The total cost of the survey with APR control showed a saving of 
approximately 23% over the estimated cost of undertaking the work 
without APR. 
5) 80% of the 192 points checked against ground levelling show no error 
greater than 5ft. and, excluding two misidentified points, 100% were 
within 10ft.. 
CONCLUSIONS 
It is believed that this is the first APR survey to be undertaken on the 
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