orrection for
uipment*
rican Multi-
based largely
eratively by
'ompany and
pervised first
er by-R. K.
beginning in
e resulted in
tive printers
rection, and
iation of the
Is of interior
he projectors
ed range and
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51 model.
PHOTOGRAMMETRIC ENGINEERING 11
Kelsh Plotter
The basic principles of this instrument,
Figure 14, were conceived by H. T. Kelsh
in 1943, prior to his association with the
Geological Survey, and were developed
by him and other members of the Survey's
technical staff beginning in 1947. This plot-
ter has passed through an extremely rapid
metamorphosis. The basic improvements
over previous double projection plotters
have, however, remained the same, namely
(1) the swinging light source, (2) correction
of camera lens distortion through adjust-
ment of the projector principal distance by
means of an arm and cam arrangement,
and (3) contact-size diapositive plates.
In 1951, an experimental adaptation of
the Kelsh plotter was constructed by the
Trimetrogon Section to demonstrate the
possibility of its use with oblique trimet-
rogon photographs.
Fic. 15. Twinplex prototype.
The Twinplex?
The prototype Twinplex stereoplotting
instrument, Figure 15, developed by R. K.
Bean, was completed in 1950. Tt is designed
to utilize low-oblique, wide-angle photog-
raphy obtained with two synchronized
and rigidly coupled cameras. (The two
cameras may be aligned either along the
flight line for precision mapping, or trans-
verse to the flight line for reconnaissance
mapping. Two unrectified diapositives,
corresponding to the two exposures made
at one camera station, are used in a set of
twin projectors. Each exposure must be
paired with an exposure from an adjacent
camera station in order to produce the
stereoscopic model. When either of the
twin projectors has been oriented in pro-
jecting position, the other projector will be
correctly oriented when it in turn is swung
into projecting position.
Stereodetailer
This instrument, Figure 16, devised by
E. I. Loud, Jr., in 1951, is used in compila-
tion review to transfer certain detail from
aerial photographs to multiplex manu-
scripts. It applies the principle of the
sketchmaster to a simple lens stereoscope.
The instrument can be visualized as a
sketchmaster in which the map and photo-
graph have exchanged positions, with a
left eyepiece added so that another photo-
graph can be viewed with the left eye to
give a stereoscopic image. Only one eye
sees the superimposed image, with the
effect that the lines of the map give the
illusion of relief, seeming to conform to the
relief in the photo model. No provision is
made for tilt, but this 1s not necessary
since it is intended to position only small
areas at a time to the abundant detail of
the completed manuscript. Enlargement
ratios ranging from two times to five times
can be obtained by changing the distance
between the eyepiece and the large mirror,
and inserting a suitable lens at the eye-
piece.
+
520
Fic. 16. Stereodetailer.