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III. PERFORMANCE VERSUS COST OF FLIGHT FUNCTIONS. 
III. 1. Survey navigation functions necessary to produce optimum - 
economy photography. 
The basic difference between navigation for survey and for other aviation purposes lies in 
the fact that the accuracy of standard avigation decreases with distance from a departure or 
destination point or radio facility, whereas the accuracy of survey navigation shall be highest 
over the survey area, at greatest distance from fixes and navigation facilities. 
As a general rule one can set the tolerance for survey flight at + and - 0. 5% absolute 
reference scale and + and - 5% lateral overlap spread and flight line linearity. This require 
ment - under the conditions as described above - is much higher than aircraft and flight 
instruments have been designed for; it is also much higher than pilots and navogators have 
been trained for. Consequently, it requires special methods which consist of the execution 
of a number of flight functions at the same time. 
For improvement of survey flight results,precision flight instrumentation is necessary such 
as gyro-magnetic, flux-gate or inertial compass, suitable autopilot, gyro-stabilized navigation 
sight or sight platform; under difficult circumstances, it is advisable to apply doppler or 
maybe even inertial navigation. The most vital tool, however, is professional knowledge of the 
specialized survey pilot and survey navigator which cannot be replaced by any instrumentation. 
As it would be beyond the scope of this paper to specify performances for each of the many 
navigational elements and navigational functions, the most important of them are merely 
listed hereunder; performance and cost are then presented for the most important types of 
survey navigation aids. 
Survey navigation elements. 
Barometric air pressure - corrected to mean sea level - at the survey area. Static air 
pressure at survey altitude. Temperature lapse rate per height.Aircraft's true air speed in 
climb, in level flight, in turns. Times, total times and time differences. Drift angles. 
Bank angles. Rate of turn. Radius of turn. Local terrain elevations and elevation differences. 
Oblique sighting angles to next flight line or to centre of side lap. Lateral overlap, percentages: 
reference, maximum, and minimum. Vertical (nadir) direction. Actual wind velocity at 
survey altitude. Compass heading, compass deviation and isogonics - Magnetic variations and 
magnetic heading. Exposure interval. Doppler speed along-track and across-track. Doppler 
drift. Doppler plus high-precision heading information plus computer *). Inertial heading, 
positioning and attitude functions. 
*) The navigational performance of Doppler is limited by its heading reference rather than 
by its inherent products ground speed and drift.