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1. Precision Aerial Mapping - The aircraft flies long 
parallel flight' lines while controlling the forward 
overlap and sidelap of the mapping camera photography 
to a high degree of accuracy, plus recording all sup 
porting data. 
2. Aerial Electronic Surveying - Geodetic control net 
works by aerial electronic surveying, commonly 
referred to as trilatération nets, are established. 
This method uses the measurement of lines between 
points. After each line in the network is measured, 
a network adjustment computation provides the most 
probable position for each station. Line measure 
ments are accomplished by a technique known as 
"line crossing". This constitutes flying an aircraft 
across an imaginary line connecting two ground 
stations while simultaneously recording the distance 
to each station and other applicable auxiliary data. 
3. Electronically Positioned Mapping Photography - 
The aircraft flies long parallel flight lines control 
ling the forward overlap and sidelap of the mapping 
camera photography to a high degree of accuracy as 
in para "1." above. In addition, the aircraft records 
the distance to several SHIRAN ground transponders 
at the instant that the aerial mapping film is exposed. 
The location of the point directly beneath the aircraft 
(the nadir point), relative to the ground transponders 
is computed. The photograph then can be placed in its 
proper position on the earth's surface. The accuracy 
of these nadir points are within twenty-four feet with 
90% probability as referred to the ground stations from 
which they were established. 
4. Horizontal Control Point Photography - If three 
SHIRAN transponders are employed with good geom 
etry, and mapping camera photography obtained with