178 THE CANADIAN SURVEYOR May, 1960 
Second-order plotters are used for the compilation of 1:50,000 maps from photo- 
graphy taken at an altitude of 9000 metres. Compilation for 1:25,000 and large-scale 
engineering plots is also produced by these plotters. 
First-order instruments are used for large-scale plotting by federal, provincial, and 
commercial agencies when second-order optical-mechanical plotters are not available. 
Except in the case of extremely detailed large-scale plotting, compilation is performed 
by one operator per machine. lt is generally accepted that the high cost of the addition 
of a second operator per machine is not justified. 
NEw DDEVELOPMENTS IN PHOTOGRAMMETRIC PLOTTERS 
STRAIGHT LINE PLOTTER 
A special photogrammetric instrument called the Straight Line Plotter has been 
designed and built by the Photogrammetric Research Section of the National Research 
Council of Canada. By the employment of this device, accurate straight lines may be 
constructed on oblique photographs. These lines may be used to control the bend of 
an aerial triangulation by using methods described in the references. 
  
Fic. 1. Photograph of the Straight Line Plotter 
The Straight Line Plotter is equipped with an optical system that makes possible 
the stereoscopic viewing of two oblique photographs. This is achieved by providing 
both viewing telescopes with (a) independent magnifications that may be varied over a 
wide range and (b) independent cylindrical lenses that can compensate for differences 
in scale changes in the x and y directions of the two photographs. With the stereo- 
scopic comparison, identifications are made with maximum accuracy, although no real