2 
INTRODUCTION 
The analytical plotter principle, as embodied in the AP-2 and 
related instruments, represents a major advance in precision stereo 
mapping systems. The simplicity of the optical and mechanical structure 
permits significant improvement in basic accuracy. The ability of the 
computer to account for known or predictable non-idealities -- earth 
curvature, atmospheric refraction, lens distortion, film shrinkage, 
systematic instrument errors, etc. -- on an easily programmable basis 
further improves the over-all accuracy that can actually be achieved. 
Also significant is the extreme versatility of the system in handling 
advanced forms of mapping and reconnaissance imagery, including high- 
resolution panoramic photography. 
With respect to operational features, semi-automatic interior, 
relative, and absolute orientation procedures greatly simplify the 
initial set-up problem. In the basic AP-2, however, actual mapping 
operation still depends on visual observation of the stereo model, just 
as with more conventional instruments. The addition of an image- 
correlation system to provide automatic stereo perception is thus a 
logical extension in further increasing the capability of the instrument. 
Such equipment has the potential for appreciably increasing the speed 
of operation and at the same time maintaining the high precision of the 
basic instrument. 
In the design of the image correlation system described in this 
paper, detailed consideration has been given to the more important 
functions normally performed by a human operator. The purpose has 
been to determine which functions are susceptible to automation, and 
how each of these might best be shared between the basic AP-2 com 
puter and other elements of the image-correlation system. The princi 
pal functions considered for some degree of automation are: 
(1) Detection of X and Y parallax 
(2) Estimation of terrain slope 
(3) Evaluation of the quality of image detail 
(4) Accommodation for image distortion 
(5) Location of fiducial marks 
(6) Searching for image detail and for conjugate imagery 
(?) Over-all control of profiling and contouring