90 SURVEY NAVIGATION, AUTHOR'S PRESENTATION 
Author's Presentation of the Paper 
This Congress period celebrates the cente- 
nary of aerial survey. In this one hundred years 
important developments have taken place, and 
a review of the present survey of navigation 
shows some fascinating possibilities. The two 
aspects of this paper are survey navigation as 
such, and determination of camera orientation 
elements in flight. 
A variety of methods and instruments is 
available for these processes, some of the older 
existing methods can supply near-perfect photo 
coverage or high accuracy camera orientation 
data. On the other hand, some new systems 
developed for supersonic speed navigation, for 
space navigation and for automatic guidance 
can now perform with an accuracy in flight 
which is of the same order as the photogram- 
metrist has always required for his orientation 
elements. Time limitations do not permit elabo- 
ration on any particular method now. You can 
find the most important characteristics in my 
paper, together with a comprehensive reference 
literature. 
At this moment, we shall restrict ourselves 
to the most important conclusions. 
I have put these conclusions together in a 
few groups and I propose for them to be dis- 
cussed in a few groups because we are dealing 
with about fifteen or twenty different methods. 
First of all, these conclusions are that in- 
strumental navigation methods are in rapid 
development to extremely high accuracies. 
Many of them can provide for near-perfect sur- 
vey navigation, and some of them even reach a 
degree of accuracy which enables the determi- 
nation of camera orientation elements at each 
exposure station. 
Now, about survey navigation. Of the various 
possibilities, a line-of-sight navigation method 
executed by a completely competent crew ac- 
cording to sound principles has been shown to 
supply near-perfect results. For instance, for 
photographic surveys, IGN’s deviations in side 
lap are not more than 5% side lap. Longitudinal 
overlaps shall be kept to a minimum with only 
a few per cent tolerance. This is in favour of an 
appreciable reduction in the number of photo- 
graphs. A longitudinal overlap can be reduced 
by using overlap regulators, either of the visual 
type or of the photo-electric automatic type. The 
use of an intervalometertimer is economical on- 
ly in small-scale photography. Once it is possi- 
ble, or has proved to be possible, to keep over- 
lap longitudinal and lateral within 5% , we come 
to a possibility which I have called “bloc photog- 
raphy”. Bloc photography, having all the nadir 
points within 5% of each ideal position, should 
in many cases be preferred to the normal strip 
photography. It provides for points common to 
six photographs, which is the optimum econo- 
my of minor control. This can be obtained in 
three ways: either by taking 90% overlap and 
rejecting three-quarters of the photographs; or 
it is obtained by individual pin-pointing of each 
photograph; or it may be made possible by 
coupling the exposure it commands to some 
automatic guidance such as Doppler, Aerodist 
or some other navigational computer. 
Doppler navigation is reported to provide 
appreciable saving in flight time, for instance 
twenty-five per cent and forty per cent savings 
are reported, and a great improvement in flight 
line positioning as compared with coventional 
operations. 
In the near future, further improvements 
may be expected from the combined use of the 
Doppler with Inertial systems or Startracking, 
and also from the use of Aerodist. 
Now about camera orientation methods: for 
elevation control we use statoscopes which give 
flying height differences, mean error of the or- 
der of 13 to 2 metres, and the radar altimeter 
which provides for ground clearance, mean er- 
ror of the order of 1 metre plus some metres 
terrain influence. Both have proven their value 
and a combination of the two is called A P R. 
This provides for terrain elevations and profi- 
les, spot heights, mean errors of the order of 
3 to 3 metres at well-defined hard points. This 
combination is recommended. 
Regarding planimetric control, that can, as 
we all know, be obtained by means of Shoran 
and Hiran and Decca; a promising new devel- 
opment is Aerodist. Its performance is expected 
to have a mean error of the order of one metre 
plus 1 : 100,000 of the distance. Verticality in- 
formation can be obtained by means of solar 
periscopes. Mean errors of the order of three 
sexagesimal degrees are possible. The horizon 
camera in its new version may prove to be of 
great importance. It gives a verticality indication 
which is expected to be of mean error of the or- 
der of three sexagesimal degrees. 
Another development of great potential in- 
terest is the new automatic inertial vertical 
which is now under trial. It gives vertical photo- 
graphs with an expected mean error of three 
sexagesimal minutes. Gyro verticals cannot be 
and will not be sufficiently accurate for photo- 
grammetric stereoscopic orientation, but they 
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