COMMISSION III 
AERIAL TRIANGULATION 
by T. J. Bracaur 
IN TRODUCTION 
General conditions and mapping requirements in Canada are particularly suitable 
for the extensive use of aerial triangulation methods. One of the largest countries in 
the world (about 10,000,000 sq km) extending from the polar regions to the 42nd 
parallel, with a 90° difference between longitudinal extremities, Canada presents the 
most difficult and challenging mapping problems. With the exception of the rapidly 
developing southern belt where most of the 17 million population live, the country is 
practically devoid of communication roads. Huge insurmountable mountain ranges 
mostly covered by snow and glaciers, vast swampy areas accessible only in the cold 
winter time, the Arctic archipelago composed of innumerable islands separated by 
many hundred kilometres of water, impenetrable bush cover in more southern regions, 
and vast and very flat prairies with particular requirements for elevation accuracy — 
these are the characteristic components of the Canadian continent. It is obvious that 
under such conditions techniques which permit the mapping of the country with a 
minimum of auxiliary field survey are most welcome. For this reason also, great effort 
has been made in the field of aerial triangulation, and as will be seen, original methods 
have been developed in Canada to solve efficiently some of the difficult triangulation 
problems encountered in the official mapping program covering scales of 1:50,000 and 
smaller. 
There is also an increasing requirement for large-scale maps in densely populated 
areas, and extensive use of photogrammetric triangulation procedures is being made 
in this field. The most important applications and developments in the field of aerial 
triangulation in Canada will be reviewed briefly in the following paragraphs. 
SLOTTED IEMPLET METHODS 
These methods are still used, particularly in mapping at the 1:250,000 scale. By 
these means horizontal control points required in photogrammetric plotting are 
established very quickly with a minimum of existing ground control. The inability to 
determine vertical control at the same time is an obvious disadvantage. The necessary 
elevation points are therefore often determined by means of radar profiles specially 
flown over the mapped areas, which is an interesting Canadian innovation used exten- 
sively, particularly in aeronautical charting. Both the classical and the stereo-templet 
methods are in use. 
SHORAN-CONTROLLED PHOTOGRAPHY 
Basically Shoran determines the x and y coordinates of air camera stations. Since 
the position of ground points is required for plotting purposes, Shoran information 
must be referred to the ground by the determination of nadir points. Depending on 
the required degree of accuracy, this can be done either in isolated overlaps or in a 
triangulation process using Shoran information. This latter procedure is more precise, 
but also requires more work. In Canada a combination of the two procedures has 
been used and the accuracy achieved has been estimated to be from - 50 to = 100 m 
in x and y coordinates, which is sufficient for mapping at 1:250,000. 
Very large projects based on Shoran-controlled photographs have been carried 
out, particularly in the northern regions of the country. However, since 1958 the use 
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