Data Acquisition 
Photogrammetric Data 
Universal first order analogue instruments are still being used in Canada to produce strip coordinates, 
however, they are gradually being replaced by non-universal first order instruments producing model coordinates, 
A few stereocomparators are being used mostly by universities and by government agencies to measure 
image coordinates, The monocomparator developed by the National Research Council, presently manufactured in 
Canada by Space Optics, is a relatively inexpensive instrument producing accurate image coordinates, Photo- 
grammetric organizations with limited aerotriangulation requirements who nevertheless desire quality results, 
will likely find this monocomparator an attractive solution to their instrument problems. 
Field Control and Auxiliary Data 
Canadian photogrammetrists have successfully pioneered the use of aerodist controlled photography as a 
method of obtaining horizontal control for medium and small scale mapping. Between 1963 and 1971, areas 
totalling approximately 2, 000, 000 km2 have been controlled in this manner, In using aerodist controlled photo- 
graphy, one difficulty is the accurate levelling of each stereoscopic model since vertical control points are not 
normally available, Original methods to orient these models in space have been devised. In some cases, auxiliary 
data such as readings on lake surfaces, statoscope and APR are used; in other cases, models generated from 
aerodist controlled photography are simultaneously integrated into the photogrammetric block and adjusted. 
Airborne Profile Recording continues to be the main source of vertical control in the hinterlands, In 
Canada, a country which has more fresh water than the rest of the world combined, the application of a computer 
program which could adjust all photogrammetric and auxiliary data simultaneously would be of paramount 
importance. An experimental version of such a program which contains the constraints that all the points of a 
lake are at the same height, is giving satisfactory results, 
Adjustment Methods 
During the period of 1968 to 1972, nearly every Canadian survey organization carrying out aerotriangulation 
relied on computer programs developed by G.H, Schut of the National Research Council. His programs were used 
for both large and small scale mapping, Many organizations modified his programs to suit their particular needs; 
in particular, routines for the automatic detection or rejection of erroneous data were added. Also, the strip 
adjustment program was modified by some to increase the size of blocks capable of adjustment. However, limita- 
tions in the method of strip adjustment became apparent when blocks of 400 photographs or more were used, With 
regard to these limitations, it should be noted that Schut's adjustment program was not designed to adjust large 
blocks, 
Because of the increasing cost of establishing horizontal ground control, particularly in the north, a program 
designed to adjust blocks of several thousand photographs with a minimum of control became a desirable alternative, 
Consequently, the Topographical Survey initiated a research project for the development of a program for the spacial 
adjustment of independent models, and also purchased a program for the rigorous adjustment of models developed at 
the Institute for Photogrammetry of Stuttgart University, Extensive tests indicated that these programs could adjust 
very large blocks with little horizontal control producing results invariably more accurate than those obtained with 
the strip adjustment program, 
Adjustment of bundles of rays is used to a very limited extent in Canada. This is undoubtedly due to the lack 
of suitable, readily available computer programs, and to the preponderance of analogue instrument for the acquisition 
of photogrammetric data, The question of whether the method of bundle adjustment is superior to that of model 
adjustment has yet to be answered for practical conditions, particularly those appertaining to Canada, 
A few small computers such as the IBM 1620 or IBM 1130 are used to process photogrammetric data, how- 
ever, the trend is definitely toward large and powerful computers such as the Univac 1108, the CDC 6400 or 6600 
or the IBM 360-65 or 50, 
Trends for the Future 
For the immediate future the use of rigorous adjustments will have the following implications: 
1, For small scale mapping (1:50, 000): 
- in the north of Canada, the existing horizontal control established for the 1:250, 000 
maps will often be sufficient; 
- re-adjustment and, in some cases, re-survey of existing control networks may be 
necessary if the control is not homogeneous; 
- the density of horizontal control points established with the aerodist is sufficient; 
- it must be possible to identify control points on existing photographs with an error 
inferior to 2m; 
- the accuracy of positions established in the north by photogrammetry is sufficient 
for many other uses than mapping, consequently; 
- aerotriangulation results will be stored for future use in a data bank,