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c) STEREOSCOPIC MAPPING WITH THE U. S. COAST AND 
GEODETIC SURVEY NINE-LENS CAMERA. William D. Harris. 
The greater angular coverage and focal length of nine-lens photographs 
improve the accuracy of stereoscopic mapping and at the same time reduce 
the density of ground control, as compared with 150 mm. wide angle single 
lens techniques. 
The nine-lens camera has a focal length of 2 1 0 mm. and covers a field 
of 130°X 130°. The composite photograph is thirty-five inches square and 
has a maximum image displacement error of 0.2 mm. As and example to 
illustrate the great coverage of the photograph, a 1 /30.000 scale print 
images an area 1 7 miles square or 289 square miles. 
Horizontal control bridging for the map by a special radial-line plotting 
procedure takes advantage of the large dimensions and high resolution of 
the photograph to minimise the mechanical errors of radial line plotting. 
The minimum overlap of photographs is 65% in line of flight and 55% 
between flight lines. This spacing is correct for stereoscopic mapping with 
the Reading plotters and at the same time every ground point is imaged on 
at least sex photographs and will be located by as many radial lines in the 
radial-line plot. Since azimuth lines (lines of centers) can be constructed 
between centers of photographs in adjacent flight lines, strong quadralaterals 
are formed to give rigidity to the radial plot and freedom from « swing » in 
the individual flight lines in the absence of control. With the above overlaps 
ten nime-lens photographs are adequate for mapping an area which would 
require 4 lines and 1 44 photographs made with 6 inch wide angle lenses. The 
vinyl-based radial line templets are used also for a graphic solution of the air 
camera tilt and flying height. The graphic solution has proven to be the most 
precise as with it all vertical control utilised. Rectification is done with a 
special camera with tilting negative and positive planes and tilting-lens as 
well as scale adjustments. The rectified photograph has a residual tilt of less 
than three minutes of arc. The great angular coverage of the photograph also 
makes the graphic determination of the actual flying height correct within 
1 0 feet in 1 5000 ft. 
The Reading plotter is a special instrument designed to accommodate 
the 36 inch square nine-lens photographs. A pair of rectified prints can be 
oriented for stereo-mapping in about an hour. The nine-lens stereo model has 
the ground area coverage of 8 models of 6 inch metrogon photography with 
standard overlaps. The 65% endlap is used for gentle rolling terrain up to 
2000 ft. of elevation difference within the model. 
The overlap is increased to as much as 75% for rugged mountain areas. 
The base-height ratio is 1.6 for an endlap of 65% and is never less than 1.1 
even in the most precipitous terrain of Alaska. The wide Angular coverage