Canada 3 
now making a useful contribution to photogrammetry in Canada. Emphasis 
is placed on the development of techniques suited to Canadian conditions rather 
than on the design of new equipment. However some minor items have been 
developed which include a steering device to control the x, v, and z motions of 
a stereoplotter, a profile recorder which registers the vertical movement of a 
multiplex table on a rotating drum and a straight line plotter used to produce 
a straight line through a series of forward facing oblique air photographs. The 
principal techniques now under study are analytical bridging, and aero triangula 
tion utilizing correlated bi-camera photography and radar altimetry. The latter 
has given very favourable results and indications are that bridges in order of 
300 km in length can be run with much greater precision than hitherto possible. 
Access to electronic computing facilities has made it possible for the Section 
to carry out investigations in the field of analytical bridging. Encouraging 
results have been obtained from the initial experimental work which was based 
on observations taken on Cambridge stereo-comparator. 
An independent development in equipment is a special plotting table 
designed for use with multiplex and known as the Gamble Stereoplotter Type 
T301. This plotting table replaces the conventional tracing table with a table 
covering the entire overlap. The horizontal plane is depicted by a grid of light 
dots projected on to the table and the vertical distance from the projectors to 
the table may be adjusted for any desired contour level. It is considered 
that this equipment will reduce plotting time and will make more effective 
use of the skill of trained Topographers. 
Photographic Interpretation 
Air photographic interpretation is being applied in Canada for topo 
graphical mapping and for military, geological, geographical, agricultural and 
forestry purposes. It is also applied to some extent in road, railway and electric 
transmission line location, as well as for various other engineering projects. 
One of the geographical applications has been the employment of aerial 
photographs in the investigation of vegetation for climatic and zonal demarca 
tions. The Prairie Farm Rehabilitation Administration has been successful in 
an interpretation of soil conditions from air photographs to facilitate irrigation 
and water development surveys. Air photographic interpretation is being 
employed in forest inventories throughout Canada. Forest sites are also being 
interpreted and a system has been developed whereby land form position and 
vegetation are employed to indicate soil moisture, parent soil material and great 
soil group. 
Non-Topographical Photogrammetry 
The usual procedures of aerial photography are successfully applied to 
such problems as the measurement of pulp-wood piles and special techniques 
have been developed for the measurement of water currents by the Parallax 
method and the determination of deformation in structures from photographic 
records. 
Some progress has been made in micro-photogrammetry for which there 
are many obvious uses. This progress has been hampered by the lack of suitable 
distortion-free lenses and the National Research Council has therefore undertaken 
the design and development of a family of such lenses.