depending on the magnitude and urgency of his 
needs. Memory can be apportioned to the users in 
similar ways. Executive programs have been devel- 
oped to control the allotment of time and memory to 
the users; these executive programs may themselves 
require substantial computation time and memory. 
Some difficulties are associated with time-sharing. 
Computer response times frequently are unpredict- 
able, making the consistent response times and repeti- 
tion rates needed for real-time instruments difficult 
to obtain. There is always the possibility that one 
user’s program will destroy the program or data of 
another user. Finally, all instruments are out of 
operation if the computer fails. All these problems 
can be alleviated with some effort. For example, 
highly reliable and quickly repairable computers are 
being developed to reduce the effects of computer 
failure on production. 
Computers can be interconnected to perform a 
variety of potentially useful functions. Several photo- 
grammetric-instrument computers might be linked to 
a large central computer to provide direct data trans- 
fer. This data might include terrain information sent 
directly from the instruments to a digital cartographic 
storage system. Conversely, the data might include 
orientation or ground control data sent to the indi- 
vidual instruments from the central computer. An- 
other potential for computer sharing is in the use of 
the large computer to perform the service programs, 
while the individual small control computers process 
only the real-time program. Finally, more highly 
integrated computer sharing could lead to a computer 
network in which the entire computational load is 
shared by all computers. In this case, failure of one 
computer need not mean complete system failure; 
most of the instruments could continue with their 
normal performance, or all instruments might operate 
with slightly reduced performance. 
Real-Time Programs 
Realtime programs can be changed to mathe- 
matically model more physical relationships than at 
present, and to more completely model the relation- 
ships presently incorporated. The use of photographic 
reseau data during stereoplotting is a possible im- 
provement in this area, as is the adjustment of photo- 
carriage positions for mechanical and thermal effects. 
Simultaneous digital recording of plotted data is 
already performed with the AS-11B automatic ana- 
lytical plotter. The use of digital data recording dur- 
ing manuscript compilation will undoubtedly increase 
with the expansion of digital cartographic data banks. 
The real-time program could be modified to perform 
30 
some data labeling and compaction before recording 
takes place. 
Software may be increasingly useful in preparing 
real-time programs. A suitable real-time-control 
compiler language may be developed. A large com- 
puter with its software may be used to prepare op- 
erating programs for the control computer. 
Finally, real-time programs may be written to 
permit accurate stereoplotting from remote sensor 
line-scan records, stereo television displays, and other 
unusual image data forms. 
Service Programs 
Service programs for photogrammetric instruments 
will continue to expand, and this expansion will ac- 
celerate as the photogrammetric control computer 
becomes more suitable for general-purpose use. À 
quantitative change can be expected: more massive 
routines will become feasible. Two possibilities are 
on-line block triangulations and least-squares interior 
and exterior orientations with sophisticated con- 
straints. There will be a qualitative change as well. 
Better languages will be developed for service pro- 
grams. Executive programs may come into wider use, 
enabling large libraries of service programs to be kept 
available for moderate-speed access. It may be pos- 
sible for the programmer to prepare and verify his 
service programs directly at the computer console. 
As automatic instruments progress, programs may 
be written to permit the computer to automatically 
perform complex orientation procedures, transferring 
from the real-time program to the service programs as 
necessary. These procedures may include large- 
volume data collection, analysis, editing, and weight- 
ing. 
User libraries of service programs will be created, 
based on service programs written by the user rather 
than the manufacturer. The research possibilities of 
such a system are extensive. The ability of the photo- 
grammetrist-user to tailor his service programs to his 
specific needs will be a significant breakthrough in 
photogrammetric man-computer interaction. 
CONCLUSION 
Whenever a control computer is added to a man- 
machine environment, new ways of thinking about 
the work inevitably arise. In photogrammetry, some 
of this thinking has been highly emotional in the past, 
perhaps caused by automatophobia, or fear of being 
replaced by a computer. More constructive thought 
FORREST, WHITESIDE, AND HORNBUCKLE