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included by the photography amounted to 4, 000 square miles and contained 2, 200 
line miles of APR record. Of this approximately 900 miles were flown independ- 
ently of the survey cover and were subsequently used for control, the remaining 
1,300 line miles being rejected either as being redundant or flown too high for 
the accuracy of the work. 
Of the total cost of the operation 1/3rd was on APR flying and 2/3rds on 
photographic flying. However with the experience now available it should be 
possible in future to limit the proportion of APR flying even further. 
APR REDUCTION AND PHOTOGRAMMETRY 
Reduction of the APR strips was carried out in the standard manner. The 
35mm exposures were used to transfer the principal points of the locating 
camera to the 1/40, 000 scale photography. By reference to the positions of the 
35mm p.ps on the profile and by stereo-examination of the main cover, it was 
possible to eliminate those p.ps which fell in areas of steep slopes or where 
the record indicated excessive noise. Possibly due in some degree to the effect 
of vegetation cover, the APR record showed over the greater part of its length 
a noise band of about 5ft. and the control value read off the record at any point 
was taken to be the mean between the upper and lower limits of the band. As a 
general rule, after disregarding the unsuitable 35mm p.ps, there remained 
three or four heights along each APR line within the area of an overlap - i.e. a 
minimum of nine APR spot heights for the setting of an overlap. As explained 
later those points falling only in the lateral profiles were eventually used in the 
photogrammetric work. 
Plan control was provided by a slotted template lay-down based on a close 
framework of co-ordinated points, shown by black triangles on Diagram A. The 
majority of these points formed part of an existing primary series carried out 
by the Federal Survey Department. The remaining points were supplied by 
Tellurometer during the same period as the height control for the reservoir 
survey. All twenty-two points used for plan control were premarked before 
photography and were therefore precisely identified on the survey cover. 
The Zeiss Secator was used for cutting the templates which were of cobex 
sheeting. No trouble whatever was experienced during the assembly to which 
the excellent flight pattern, the accuracy and precise identification of the 
control points, and the relatively flat nature of the country (the total height 
relief in the area did not exceed 150ft.) all no doubt contributed. 
As already explained a number of control strips were flown at low level in