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for large scale (1/50,000) map compilation. However, the new surveying 
system will have the ability for instantaneous distance recording from any 
or all of the four ground stations. This feature is a key element of the 
new concept which makes possible the accomplishment of what I termed 
"Control Point Photography". Control Point Photography can be obtained by 
recording the simultaneous airborne distance measurements from three or 
four ground stations encircling the aircraft which will pinpoint it for a 
strong geometric fix. The geometric fix synchronized with the mapping 
camera exposure along with its vertical deflection of less than 30" arc 
(3 sigma) will permit each photo nadir to be plotted to a probable error 
or 15' within the trilateration net. 
From an operational standpoint, control point photography is a very 
desirable technique since scattered to broken cloud conditions would be 
no hindrance to the aerial surveyor. Since 3/10 to 5/10 cloud cover is 
the normal weather condition that can be expected 90% of the time in the 
majority of areas of the world, a dense network of stereo, control point 
photos could be easily obtained where the ground is not obstructed by 
scattered or broken clouds. 
The operational procedure would call first on the ground stations to 
be installed in an appropriate network pattern. As soon as the ground 
stations are installed a trilateration net can be flown. While these 
ground stations are in place a dense network of Control Point Photography 
can be acquired which will precisely locate the nadir of each of the 
stereophotos throughout the project area. 
Compilation to satisfy horizontal control criteria for the required 
1/50,000 scale maps should be possible with approximately 50% area 
coverage by means of Control Point Photography. In addition to the 
trilateration net and Control Point Photography of the project area, a 
terrain profile will be obtained by the aircraft's Airborne Profile 
Recorder (APR) for vertical control. The high precision inertial platform 
will also assist in the vertical determinations as it will be possible to 
record the air station base line between successive aerial photos with a 
probable error of 5 feet. The air station base line distance, the precise 
vertical deflection and the hypsometer recordings of the profile recorder 
will provide the raw data and geometry for contouring stereo photographs. 
Complete visual aerial mapping of each project area will be obtained when 
good photo weather prevails. The visual photo operational phase will not 
normally be accomplished during the same period in which the trilateration 
net and the control point photography is accomplished.* This procedure is 
more fully explained in the next section entitled "An Operational Concept 
for Map Data Acquisition." 
*Note: Flight line navigation will be guided by the high precision inertial 
platform and updated as required by the versatile optical view finder. 
5