4 
I mentioned earlier that Hiran Controlled Photography was not operationally 
feasible except in the very good weather areas, but there is another 
technique used with the present Hiran system that has been successful which 
is called Secondary Control Photography (SCP). It is used to locate a 
pinpoint target such as an off shore island or an inaccessible point when 
first order accuracy is not required. The SCP technique does not require 
a large clear weather area, only the pinpoint target need be unobstructed 
by clouds. 
Secondary Control Photography is obtained in the following manner. 
While the aircraft is accurately and continuously positioned in space in 
relation to two ground stations, a series of photographs are taken on each 
of four flight paths. The operational flight pattern is designed to cross 
the target (SCP) in an X pattern of each of the four cardinal compass 
headings. A minimum of 13 aerial mapping photographs are taken on each 
flight path. The combined total of 52 exposures is centered on the (SCP) 
target. This large number of photographs are then analyzed for the most 
probable position by relating the distances measured on each of the four 
flight paths. The final computed position of the secondary control point 
(SCP) would have an expected accuracy of better than 50 feet. 
This current SCP technique can be radically upgraded in accuracy with 
incorporation of the 30" vertical in the new mapping and survey systems 
under development and is called Control Point Photography rather than 
Secondary Control Point Photography. 
The past and present method of map compilation from aerial photographs 
has depended to a large degree upon the ground surveyor's accomplishments. 
The ground surveyor's task is slow and laborious, and in addition, he is 
unable to traverse much of the world's primitive and impenetrable areas. 
A system that relies solely on the ground surveyor's accomplishments to 
compliment aerial photography will not satisfy todays mapping requirements. 
A new aerial electronic surveying system called Shiran has been 
developed and tested in the U. S. Performance specifications required a 
precision measuring capability of 6' accuracy for measurements up to 450 
miles line of sight distance from each ground station. Development 
specifications dictated that a high order of reliability be built into 
this system. The results to be recorded on digitized tape and compatible 
with out electronic computors. The new system will also permit the 
aircraft to record four channel measurements simultaneously from widely 
separated ground stations which will greatly strengthen its potential as 
an airborne surveying tool. 
When this system becomes operational, a trilateration network of 
aerial electronic measurements, with ground stations separated 100 to 500 
miles, will provide a basic geodetic framework of 1st order horizontal 
control. This density for the geodetic framework is, of course, inadequate