1 
1. 
INTRODUCTION 
The extension of control by photogrammetric methods in unmapped 
territories is one of the most challenging tasks of photogrammetric engineering. 
Many aerial triangulation methods have been developed, based either on the 
analogue or the analytical approach to the problem. The ultimate aim is to 
devise a photogrammetric system which would permit compilation of maps from data 
collected by airborne instruments, thus effecting a very considerable reduction, 
if not complete elimination, of ground control surveys. The use of auxiliary 
instruments, such as the horizon camera, Doppler navigator, and statoscope, 
together with the aerial camera, is a step in this direction. 
Aerial triangulation techniques, based on a successive orientation 
of one photograph to the next, are limited to a large degree by a double 
summation of accidental and systematic errors. This limitation exists when 
analogue instruments, such as the Wild A-7 and Zeiss C-8, are employed, as well 
as when stereo-comparators or mono-comparators and analytical methods are used. 
The only hope of eliminating this unfavourable summation of errors 
lies in the introduction of additional data obtained from auxiliary instruments 
installed in the survey aircraft. One of the auxiliary instruments introduced 
again to photogrammetry is the horizon camera. The horizon camera is the only 
instrument commercially available that can provide tip and tilt information with 
a high degree of accuracy. It is simple in construction and operation, and is 
relatively inexpensive. 
The Doppler navigator, developed originally for military purposes, 
was quickly adopted for civilian photogrammetric applications. It guides the 
aircraft on a survey flight and triggers the aerial camera at predetermined 
intervals, thus determining the distance between each exposure station. 
The statoscope gives the difference in elevation between exposure 
stations relative to an isobaric surface. This instrument has been used in 
aerial triangulation for some time. Introduction of these auxiliary data, 
particularly the tip and tilt derived from the horizon camera, into the bridg-