flight aerial photography is obtained and three distances 
from the aircraft antennas to three known geodetic stations 
are measured simultaneously. Knowing these distances and the 
height of the aircraft, as well as the position and elevation 
of the geodetic ground stations, the coordinates of nadir 
points of each aerial photograph can be computed. The 
accuracy of position of nadir points determined in this way 
is in the order of *5 m, to * 7m. Aerodist-controlled photo- 
graphy is flown in a grid pattern. When the mapping photography 
is at a scale of 1:50,000, Aerodist-controlled photography 
should be spaced at 60 kilometer intervals in the direction 
perpendicular to the flight lines of the mapping photography 
and at approximately 100 kilometer intervals in the direction 
parallel to the flight lines of the mapping photography. 
The procedure of transferring the control from the 
Aerodist-controlled photography to the mapping photography 
is briefly as follows: 
The coordinates of the nadir points are plotted on 
a manuscript. The stereo models are set up in an instrument 
such as the Wild B.8, levelled using horizon camera data, then 
the nadir points for each photograph are determined by placing 
the space rods in vertical position. The scale of the stereo