It is reasonable to expect that the scanning accuracy will be 
enhanced by the improved viewing conditions and the reduction in operator 
fatigue. The geometric faithfulness of the resulting orthophotographs is 
directly dependent upon the scanning accuracy. Where it is intended to 
use the profile data as hypsometric information, the accuracy of scanning 
is vitally important. 
Another significant innovation is the insertion of self-synchro- 
nizing mechanisms in the transmission of x-, y-, and z-motions to the 
scanning assembly. 
A constant-speed electric motor is used to power the x-motion 
of the scanning carriage. This motor rotates a generator selsyn that 
governs the rotation of a motor selsyn. The reacting motor selsyn turns 
a lead screw that drives the scanning carriage along its path in the 
x-direction on the cylinder assembly. At the end of each scanning path 
the carriage trips an electric switch that activates the set-over mechanism 
for the synchronized motions in the y-direction. 
The z-motion of the cylinder assembly is controlled manually 
through a handwheel mounted on the operator's chair. The handwheel 
rotates a generator selsyn that transmits the mechanical rotation of the 
handwheel electrically, through a flexible cable, to a motor selsyn 
mounted on the Orthophotoscope. This motor selsyn controls the rotation 
of a lead screw that provides the z-motion for the cylinder assembly. The 
scanning operation, which requires that the elevation of the scanning 
aperture be adjusted continually to remain in contact with the surface of 
the stereomodel, is facilitated by this arrangement. As the operator moves 
forward slowly to maintain a desirable and nearly constant viewing relation- 
ship with the scanning platen, the manual control for the z-adjustment 
moves with him. Eliminated are the awkward postures formerly required of 
the operator as he observed the scanning platen in its various positions 
throughout the area of the stereomodel and, at the same time, had to reach 
and make critical adjustments with a manual control located on a stationary 
mount. 
The servomechanical response of the x- and z-motions is positive 
and extremely smooth and represents. a considerable improvement over the 
mechanical-linkage action of the earlier instruments. However, the primary 
reason for the incorporation of synchros in the new design is the capability 
of each generator selsyn to function as a master for more than one motor 
selsyn. Additional motors, remotely located, can be made to respond to the 
electric currents induced by the generator selsyns on the Orthophotoscope. 
In this way the three coordinate motions of the scanning carriage can be 
reproduced or recorded by other instrumentation physically distant from the 
Orthophotoscope. The capability is thereby established for using the 
profile data of each scan, simultaneously or subsequently, to operate other 
image-restitution equipment and model-carving equipment, and to extract 
hypsometric information in digital or analoa form. 
The importance of the development of practical means for obtain- 
ing uniform scale photographs has been recognized. The Orthophotoscope's 
compatibility with ànd applicability in automatic photogrammetric mapping 
systems may be of still greater significance. Available now from the 
scanning procedure are records of mapworthy planimetric and hysometric 
information in the form of orthophotographs and profile data. At present 
only the z-component of the profiling exercise is not fully automatic. 
However, if the development and refinement of electronic sensing devices 
such as the Automatic Scanning Correlator continue at their present rate, 
it should not be long before the valuable products of the Orthophotoscope 
are obtained in a completely automatic eperation. 
6 INT,DUP.,D.C.60- 77113