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86 SURVEY NAVIGATION, CORTEN 
CONCLUSIONS. 
General. 
Instrumental navigation methods are in rapid development to extremely high accura- 
cies; many of them can provide for near-perfect survey navigation; some of them reach a 
degree of accuracy which enables the determination of camera's orientation elements at 
each exposure station. 
Survey navigation. 
Of the various possibilities, a line-of-sight navigation method executed by a completely 
competent crew 1) according to sound principles has shown to supply near-perfect results 
(for topographic surveys IGN’s variations in side lap are not more than 5%). 
Overlaps shall be kept to a minimum, with only a few percent tolerances, in favour of 
appreciable reduction in the number of photographs. Longitudinal overlap is reduced by 
using overlap regulators, either of the visible type or of the photo-electric automatic type. 
The use of an intervalometertimer is uneconomical. 
Bloc photography, having all nadir points within 596 of the ideal position, should, 
in many cases, be preferred over strip photography. It provides for points common to six 
photographs which is optimum economy of minor control. It can be obtained in three ways: 
either by taking 9096 overlap and rejecting ?4 of the photographs, or it is obtained by 
individual pin-pointing, or it shall be made possible by coupling the exposure command to 
an automatic guidance such as a Doppler (or an aerodist) navigational computer. 
Doppler navigation is reported to provide appreciable savings in flight time (25% 
and 4096 savings) and great improvement in flight line positioning as compared with 
conventional operation. 
In the near future, further improvements may be expected from the combined use 
of Doppler navigation with inertial systems and star tracking, and from the use of 
aerodist. 
Camera orientation. 
For elevation control, statoscope (flying height differences, m, — = 1,5...2 m) and 
the radar altimeter (ground clearance m, — -- 1 m plus one or more meters terrain influ- 
ence) have proven their value. The combination of these, APR (terrain elevations and pro- 
files, spot heights m, — - 1.5... 5 m at well-defined hard points) is recommended. 
Planimetric control can be obtained by means of shoran and decca; a promising new 
development is aerodist (expected m, , — +1 m + 1/100.000 distance). 
Verticality information can be obtained by means of the solar periscope (m, ; + 8e 
is possible) ; the horizon camera in its new version may prove to be of great importance 
(verticality indication expected m 
a, p 7 # 3°); another development of great potential in- 
terest is the new automatic inertial vertical now under trial (vertical photographs, expected 
m, p= = 3°). Gyro verticals can and will not be sufficiently accurate for photogrammetric 
stereoscopic orientation; they can be used for planimetric mapping purposes (verticality 
information errors m, 4 10’...20’; one highly corrected gyro system performs 
m, 5 = 5 ...10") and for the use of 3rd order plotting instruments. 
In many cases single methods alone are incapable of performing with highest ac- 
curacy (compass, gyroscope, inertial instruments, etc.); there is a trend towards com- 
bining various methods — each one with their particular merits and deficiencies — into 
integrated precision navigation systems such as: Doppler plus dead reckoning, inertial 
plus Doppler, inertial plus star tracking, Doppler plus star tracker on inertial platform, 
etc. In this way, they can be made to limit each other's error propagation and instrument 
1) navigators of this class are of a pilot's educational and experience level.