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handled in the incremental section of the computer, as are the photo
graph position computations in the standard AP-Z. In order to make
integrators available for the additional computations, several elements
of the photo position computations are modified or shifted to the whole-
number section. Specifically, the separate corrections available in the
basic instrument for systematic effects and model distortion are com
bined, and the air refraction correction is simplified. The compu
tations for optical magnification and image rotation, which are slowly
changing parameters used to control zoom lenses and Dove prisms in
the viewing optics, are moved to the whole-number section.
The functions of detecting loss of correlation, searching to re
cover correlation, and indexing between plotting lines, are performed
in the whole-number section of the computer. The whole-number
program also controls the computation of the partial derivatives re
quired for the scan shaping process; in fact, these same derivatives
are used in the optical magnification and rotation computations. The
calculation of the basic partial derivatives is executed at a relatively
low rate since these parameters change rather slowly with motion
through the model. However, the computer output information which
controls the scan pattern shaping in the correlation system is updated
in the incremental section to reflect changes in terrain slope at the
normal computation rate of 100 times per second.
In the basic AP-2 instrument, the whole-number section of the
computer is fully utilized only during the set-up and orientation pro
cedures. Therefore, the above functions, which are required mainly
during contouring and profiling, can be handled without addition to the
basic computing capability. The only modifications required in the
computer are an expansion of the whole-number memory to permit
storage of the larger programs and an expansion of the input-output
section to provide communication with the correlator electronics.
CONCLUSION
The addition of an image correlation system to the AP-2
analytical stereoplotter extends the capabilities of the basic instru
ment for faster and more automatic production of contour and profile
charts from any of several types of photography. The expanded instru
ment makes effective use of the control, computational, and decision
making abilities of the AP-2 computer to provide not only a highly