Thus, improving the automatic stereoperception pro- 
cess, either by increasing its sensitivity or by increas- 
ing the amount of information sensed, is one poten- 
tial area for further improvement. 
A second approach for system improvement is 
expansion of the functions performed by the com- 
puter and its programs. With additional data process- 
ing, the computer can potentially make better use of 
the correlator outputs, provide additional smoothing 
and editing for the plotted manuscript, and make 
additional contributions to the overall control of the 
plotting process. 
The following paragraphs describe several of the 
more promising hardware and software approaches 
for compilation system improvement. 
Improving the Correlation Process 
Recalling the previous description of the automatic 
stereoperception system, the scan pattern is shaped to 
provide a plane-surface approximation to the terrain 
at the point of interest, and the size of the pattern is 
adjusted by the computer to the smallest value con- 
sistent with the available image detail. Considering 
only the static aspect of the stereoperception prob- 
lem, that of placing the floating mark on the terrain 
surface with greatest possible accuracy, this is clearly 
a logical approach: it duplicates the operator’s func- 
tion in point measurement by concentrating on the 
image detail immediately adjacent to the optical axis. 
During compilation, however, when the point of 
interest is continuously changing, the approach of 
concentrating on the smallest possible area has serious 
deficiencies. The terrain-slope and parallax informa- 
tion, from which the computer derives the steering 
commands, will tend to be noisy due to microrelief 
and, more seriously, it will contain no information 
about major terrain features until they are very close 
to the reference mark. It is necessary, of course, to 
retain the capability to measure elevation accurately 
at the optical axis during compilation. However, it 
would be highly desirable to expand the area scanned 
to derive better steering information. 
The center-gating technique for the elevation error 
signal discussed earlier represents a first step at allow- 
ing scan size to be increased. However, in the problem 
areas of rough terrain, it is clear that the basic limita- 
tion to using a larger scan size is the plane surface 
approximation to the terrain, which is implicit in the 
first-order scan pattern shaping. 
The above discussion leads to the conclusion that 
larger scan areas would be possible and better steering 
information could be developed, if the scanning pro- 
cess were made adaptive to the terrain curvature and 
roughness by the use of second-order or higher scan- 
10 
shaping corrections. This approach also improves the 
image registration and reduces the individual point 
parallaxes within the scanning pattern, and it tends, 
therefore, to improve the sensitivity and accuracy of 
the scanning and correlation process in addition to 
developing better steering information. 
The use of higher-than-first-order scan shaping is 
clearly consistent with the capabilities of the flying- 
spot scanners. However, it does imply substantial 
expansion (1) of the video correlator to sense addi- 
tional parameters related to terrain curvature and 
roughness, (2) of the computational load on the 
computer to compute additional scan-shaping control 
information, and (3) of the scan generátors to gen- 
erate more complex scan patterns. For example, as 
each order of scan shaping is added, the x-parallax- 
related outputs of the correlator must be expanded 
according to the following table: | 
  
  
Total 
Relation to Number of Number 
Correction Terrain Within Correlator of 
Scan Pattern Outputs Correlator 
Added Outputs 
Zeroth Average elevation 1 1 
First Average slope 2 3 
Second Average curvature 3 6 
Third Average rate-of-change 4 10 
of curvature 
  
  
  
  
  
  
Fortunately, because of recent advances in com- 
puter and electronic circuit technology, the required 
expansion is highly practical. As described in an 
accompanying paper,* the real-time computational 
capabilities are greatly increased in the new inte- 
grated-circuit, core-memory computers. Similarly, the 
application of linear integrated-circuit techniques to 
the analog signal generation and processing circuits in 
the scan generator and video correlator has resulted in 
a substantial simplification of this equipment and will 
make feasible the implementation of much more 
complex functions. 
One limitation of the present correlation tech- 
niques which cannot be solved by the above tech- 
niques is the limited sensitivity of the flying-spot 
scanners in the presence of high-density or low- 
contrast image detail. Thus, no discussion of this area 
would be complete without a comment on the alter- 
natives to the flying-spot scanner. One that is cur- 
rently the subject of substantial research is the appli- 
cation of coherent optical correlation techniques to 
*V. C. Kamm et al, "Design of the Bx-272 Integrated-Circuit Con- 
trol Computer." 
CHAPELLE, WHITESIDE, AND BYBEE 
Output Signal- To- Noise Ratio (S/N) 
FAX aub FR'AV G^ — Gua aui, 
Ce) e^ S ou fF" 6 e eR I^ mw] uh Da 
CL m "o m: 
i 
es