The New York herald., 1922-01-22
Camera Maps

TT is said that among the most accurate
Of maps are those made with the
camera Engineers in the Government
employ have, it is reported. completed sur
vey from which maps have been made OF
several thousand square miles in Alaska
More than thirty thousand square miles on
the boundary line between the United States
and Canada have also been mapped with the
camera.
With the rapid development of the air
plane and the dirigible balloon in European
countries came corresponding development
of aerial photography for military purposes
and "a new awakening to the real value OF
aerial photography for surveys other than
those of military character. French en-
gineers have indorsed the aerial methods of
Photographic surveying as both rapid and
economical.
An apt illustration of this fact is found in
the survey and resulting map of Prince
William Sound. Alaska. Here the noun
tains rise from two thousand TO ten thou
sand feet above the waters edge Two
cameras placed in forty foot motor boa
were used by Government engineers in max
ing survey of 1000 square miles of terri
tory. The boat was run 220 miles and 22O
pairs of pictures were taken during the
cruise which lasted ffty-eight hours
From these pictures an accurate map of the
region has been made. To have made the
survey and map under former methods
would have required months of difficult and
expensive travel on the part OF the en-
gineers
II is not commonly realized that photo
graph of a plane surface taken with plate
camera directed perpendicularly toward thai
plane Is map of the area which the photo
graph embraces. In other words, it ss
possible to use the camera to produce charts
in the form of negatives, of level ground
provided the camera can be placed in a po-
sition directly above the ground. Here the
camera will merely be doing on a small
scale what is done on a much larger scale IN
map reduction by photography.
Engineers use the panoramic camera IN
making surveys of mountainous regions and
for aerial flying positions. The camera r.
set up on the side of the mountain, over
looking a considerable section OF surround
ing country. possibly several square miles IN
total area. The maps are made from the
panoramic photographs. IT having been de-
cided at what altitude the photos were
taken. II is comparatively an easy matter
to determine the altitude OF various points
i'm the pictures.
The panoramic camera consists of a box
made OF aluminium, inclosed in n protecting
frame of mahogany. and this is lined with
felt. Inc top of the box II the reference
plane for leveling and the vertical axis
carrying the lens Is placed perpendicular to
this plane. The circular film guides are ad-
justed so that when the film Is In position
for exposure all elements will be perpendlcu-
lar TO the level plane and hence parallel 70
the lens shaft.
The panoramic camera used In making
maps is OF two types. one employing a five
inch film cartridge and the other n six inch
cartridge Two films are carried in each
machine. and after one has been "shot" the
camera Is swung around and the other
film exposed. The camera Is held In a per-
fectly level position by means OF wire kuys
That the camera presents an accurate
rneans OF making maps Is we'll illustrated
by the fact that in DO recent Alaskan sur-
veys. Government experts discovered b.
checking up their cumulative error in verti
cal angulation. that the error amounted to
but twenty-five feet in one hundred miles
In a late survey the error in 250 miles was
but sixty feet and this was stretched
over some one hundred stations the aver
age error was less than one foot for esch
station.