SURVEY NAVIGATION, CORTEN 61 
a. to new methods which may be of importance to photogrammetry in the near future; 
b. to conventional methods that need some special remarks. 
The two aspects of this report are airborne navigation and airborne determination 
of camera orientation elements. Until recently, these two were completely separate fields, 
the former being not nearly as accurate as the latter. However, the demands to super- 
sonic speed navigation, to spatial navigation and to automatic guidance have become so 
extremely exacting that the methods and instruments developed for these purposes must, 
in future, perform with the same accuracy in flight as the photogrammetrist has always 
required for his orientation elements. 
It is not possible to determine all elements in flight with sufficient accuracy to be 
used for photogrammetric orientation without reference to ground control. Some of the 
older and some of the newest methods, however, are capable of 
a. producing near-perfect photo coverage; 
b. supplying camera’s orientation data with sufficient accuracy for greatly economizing 
photogrammetric control. 
In establishing these elements, the performance of the methods is such that the ac- 
curacy of each individual measurement is not as high as the accuracy of the photogram- 
metric orientation. The influence of their errors, however, is mainly of a constant nature: 
the error propagation is negligible as compared with the propagation of the photogram- 
metric orientation errors. 
Their application is still limited mainly to their use as “auxiliary data for aerial 
triangulation” but with the advent of some highly accurate systems this situation may 
change in the near future. We refer to Brandenberger in Comm. III [4a] and to Schermer- 
horn in Comm. IV [4b]. 
1. Purely navigational methods. 
1.1. Dead reckoning navigation. 
Principle. 
Dead reckoning navigation (DR) is based on the knowledge of a starting point posi- 
tion; if the vectorial components of the airplane’s movement (i.e. speed and direction) 
are known, these can be integrated over the time to give the displacement from the 
known point and, consequently, the present position. 
A number of corrections must be applied such as corrections for compass deviations, 
drift vectors, etc. 
Because the DR errors can be larged and are always propagating, the final result 
is of insufficient accuracy to be used in survey navigation. In addition, the time con- 
suming computations and the determination of fixes necessary to correct for the DR error 
propagation make its application to survey navigation of very doubtful value. 
Remarks. 
Some of the newest navigational methods, however, are capable of determining the 
displacement values with extremely high accuracy; examples are inertial navigation and 
Doppler navigation. In addition, they can be coupled onto computers to present the 
results immediately in any coordinate system or in the form of a command to the auto- 
matic pilot. 
These methods (coupled with the proper computers) can be considered as modern 
versions of the dead reckoning navigation. They become of great value for survey navi- 
gation and are dealt with in paragraphs 2.3 and 5.2. 
1.2. Contact navigation. Visual navigation according to line-of-sight. 
Most aerial photography missions are applying visual methods of survey navigation.