i 
G 
2 
ing procedure eliminates the double summation of errors and, consequently, 
cancels the need for vertical control in the center of the strip. 
Canadian Aero Service Limited has successfully employed the 
horizon camera, Doppler navigator, and statoscope on projects in Nigeria 
involving mapping at 1:50,000 with 50-foot (15.5-metre) contours of some 
o 
100,000 km , on a project in Gabon involving mapping at 1:5,000 with 10-metre 
contours for a 1000-km long railway, and on a project in northern Canada 
involving extension of control in an area of some 11,000 km^ for mapping at 
1:50,000 with 25-foot (7.8-metre) contours. 
The horizon camera is presently being used on an Aerodist survey 
project in Canada as an integral part of a mapping system which permits an 
accurate determination of x, y, and z coordinates of the nadir point of each 
vertical aerial photograph. The tip and tilt of each photograph at the moment 
of exposure, determined from the horizon camera, is used for location of the 
nadir point of each Aerodist-controlled vertical photograph. 
To date we have processed close to 5,000 horizon photographs and 
successfully carried out aerial triangulation. We utilized the tip and tilt 
information derived from the horizon camera in addition to data provided by 
Doppler navigator and statoscope. This practical experience yielded a large 
amount of data for a critical evaluation of the mapping system. 
This paper will discuss this mapping system, the methods employed 
in aerial triangulation, and the results achieved. 
2. HORIZON CAMERA 
2.1 General Description 
The function of the horizon camera is to determine the relative tip 
and tilt of each aerial photograph at the moment of exposure. 
The first horizon camera was developed in Finland by Nenonen in 
1928 and was manufactured by Zeiss Aerotopograph Company. It photographed the 
horizon in two perpendicular directions. The results obtained in experimental 
working using this horizon camera, by von Gruber, Schermerhorn, Neumaier,