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STEREOSCOPIC MAPPING WITH THE U.S. COAST AND GEODETIC
SURVEY NINE-LENS CAMERA
by
William D. Harris.
It is doubtful that the nine-lens camera would have been developed if so
many difficulties had not been encountered in using single-lens cameras to
make photogrammetric surveys of coastal areas. Much of the coastline of the
United States and Alaska is so irregular that single-lens photographs will not
span across rivers and bays or from the mainland to offshore rocks and islands.
The nine-lens camera has not only solved the problems involved in mapping
coastal areas, it has proven to have many advantages over the single-lens
camera in every type of mapping problem.
The 210 mm normal angle lenses which are used in this camera give pho-
tographic resolution and scale comparable with the normal angle lenses often
used for large scale single-lens mapping. Resolution is further improved by less
camera vibration possibly due to the massive rigid construction of the camera.
The nine-lens camera has never been given a formal airborne resolving power
test with the standard high contrast resolution targets but it is not uncommon
to observe the low-contrast plow furrows in farmlands reproduced in the final
print at a spacing of 18 to 20 lines per millimeter. The camera covers an angular
field of 135 degrees which gives a base-height ratio of 1.6 with an overlap of
65 per cent. The ground area coverage is nine times that of the wide-angle 6
inch single-lens camera at the same flying height and sixteen times as much at
the same scale. To illustrate the great coverage of the photograph, a 1: 30,000
scale print images a square 17 miles of 27 kilometers on a side. The area covered
is 289 square miles. — .
The photograph is 35 inches square and has a principal distance of 8'/.
inches. The maximum error of image position is 0.15 mm from that of a cor-
rect perspective view. This precision in fitting the nine separate views into a
single composite photograph is obtained by careful adjustment of the air
camera and appropriate adjustments of the transforming printer to care for
variations in dimensions of the film air negative. An airborne performance test
is made each year, by photgraphing some eighty ground targets which have
been located by first and second order triangulation and leveling. The elements
of the transforming printer are then adjusted to make a correct photograph of
the ground test area and the position of fiducial marks thus obtained is dupli-
cated when making subsequent prints.
Probably the most outstanding features of the nine-lens process are that it
requires only about one third the usual amount of horizontal ground control
and that the control may be established independent of the photographic plan.
This means that the control can, if necessary, be established in advance of the
aerial photography; that there are no special control position requirements,
such as two points in the first model of each strip of photographs. It also means
that usually all control can be established by triangulation using such objects
as chimneys, steeples, water tanks, mountain peaks and pinnacle rocks. There
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