moment of exposure (Fig. 1). The Aerodist simultaneously 
measures distances from the aircraft antennas to three ground 
stations. The APR provides the height of the aircraft above 
sea level, and the horizon camera determines the tip and tilt 
of the aerial camera at the moment of exposure. 
The Aerodist system is basically an airborne 
tellurometer system. It has been described in detail in a 
number of publications, therefore it will not be necessary 
to describe it again (2),(3),(4). In this paper the Aero- 
dist and other instrumentation will be discussed as part of 
the mapping system. 
The Aerodist fulfills two functions: 
(1) Establishment of basic geodetic control. 
(2) Establishment of secondary horizontal mapping control. 
The network of vertical control is established by 
APR, which permits the transfer of sea level datum deep into 
the project area. It is employed to replace conventional 
levelling; and when used properly it is capable of establishing 
vertical datum over distances of 300-400 kilometers with an 
accuracy of 5 meters. 
The statoscope is not an absolutely necessary element 
of the mapping system when the horizon camera is used but it