of change of direction is low. Ina navigation system, the calculation of lati- 
tude and longitude require that the distance traversed be known in direction as 
well as magnitude. A Navigation system must be oriented to True North (or 
some other fixed point on the Earth's surface). This adds enormously to the 
system complexity. 
The Navigation System also requires extensive computation to convert 
the integrated distances into change of latitude, longitude and heading. This re- 
quires many computing elements. A Navigation System cannot, in general, 
merely drop this computation to convert to a vertical system. The coordinate 
system is usually chosen so that computation of latitude, longitude and true 
heading are necessary steps in maintaining the vertical. The coordinate system 
chosen for the Aeroflex Photogrammetric Vertical Reference results in an in- 
herently simpler system. 
Because of the favorable choice of coordinate system, neither computa- 
tion of coriolis accelerations nor maintenance of highly accurate time standards 
are necessary. 
In addition to the previously stated simplifications, there are a number 
of positive advantages in the Aeroflex Photogrammetric Vertical Reference Sys- 
tem. These can be listed as: 
1. There is no indeterminacy at the geographic poles, or elsewhere. 
2. Errors are essentially independent of time or manner of flight. 
3. The simplification permits less cascading of computation, reducing 
errors. 
4. Reduction in the system size and weight permit location of the refer- 
+ 11 = 
AR 
     
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