188 THE CANADIAN SURVEYOR May, 1960 
During the period 1956 to 1960, the Photogrammetric Section of the National 
Research Council of Canada developed and perfected a technique that uses correlated 
bi-camera and airborne radar profiles. In this application, a forward oblique view is 
taken to control the azimuth of long aerotriangulation bridges of vertical photographs, 
and the information obtained from the radar profile is used to control the scale and 
vertical elements of the strip. 
This technique has been used with considerable success to strengthen the perimeter 
control of areas being mapped and to reduce the amount of ground survey work. Long 
bridges, up to 300 km, can be run with much higher precision than conventional 
bridging and considerable rigidity can be added to the compiling without resort to 
additional ground survey control. 
LARGE-SCALE MAPPING 
A considerable portion of the mapping at the scale of 1:25,000 and most of the 
work at larger scales is carried out by the privately-owned and -operated commercial 
mapping agencies. The commercial mapping agencies in Canada are equipped for and 
undertake a very wide range of work, from single small engineer projects to very 
extensive mapping at small scale or photographic coverage program. In size, the 
agencies vary from small companies to a few very large companies with international 
affiliations. These large organizations maintain research laboratories and usually have 
continuing development programs. 
Although no figures are available on yearly output in square miles, the demand 
for large-scale work, such as maps and plans for assessment, town plans, road and 
railway location, engineer plans, forestry assessment and inventory, agriculture studies 
and other work, has been steadily increasing. The indications are that requirements 
for this type of map or plan will continue to grow, both in quantity and range of 
application. As a rule, the control is supplied for every model, for publications at 
scales between 1:500 to 1:5000 and the contour interval varies from two feet to five feet. 
Probably the most significant of the new applications and techniques has been the 
combination of the photogrammetric plotting instrument and the electronic computer 
to solve engineering problems related to highway and railway locations, earth removal 
or similar type of quantitative determinations. 
Cross-section profiles are read on the plotting instrument for desired areas of study. 
The position and elevation of the points along the profile are recorded on tape auto- 
matically. To compute the slope data and other quantities, the tape is fed into an 
electronic computer together with the design criteria and information for the type of 
material along the route. The computer calculates the quantities of the cut and fill, 
classified according to the type of material as well as the vertical curves and distances 
from the centre line and also the elevation for each selected point on the slope. 
These data can be used to prepare documents for contract and also for the staking 
of the final route selected. A graphical presentation of the cross-section can be 
obtained by feeding the tape into an instrument called the Electro Dataplotter. ‘This 
instrument draws the cross-section automatically from the tape or cards. 
The combination of the photogrammetric plotting instrument with automatic 
electronic recording and the electronic computer makes the determination of earth work 
quantities and slope staking data much quicker and cheaper than using ground survey 
methods. 
A further application is the determination of the pay quantities. After construc- 
tion of a railway or road or at any time during construction, the route can be re- 
photographed. Cross sections on the new photography are read and recorded on tape. 
The two tapes, one made before work commenced and the later tape when work had 
progressed, are fed into the computer along with the information concerning the type