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The role of digital components in photogrammetric instrumentations

Gleaning out trends from the impacts of such a bewildering torrent
of new technology is not easy. Yet, there are clear trends. There is,
for example, a clear trend toward reduction of interconnections. Inter
connections are a notorious source of trouble, not only physically, but
also conceptually in terms of logic and timing. Similarly, and perhaps
not totally independently, there is a trend toward moving functions from
hardware to firmware, and from firmware to software, whenever the speed
requirements can be met. (An exception to this is the computer main
frame application, where decreasing hardware cost has led to a trend
of adding hardware to reduce software development costs.) Steadily de
creasing memory module cost supports continuation of these trends.
A direct result of the availability of microprocessors and their
popularity as means to implement random logic has led to another clear
trend: use of distributed processing. In its purest sense, distributed
processing means incorporation of computers into data originating stations
"Smart" terminals, point-of-sale terminals, and "intelligent" instruments
in a data collection system are typical examples. Similar concepts are
favored for automation of manufacturing. The kernel idea is to perform
whatever processing is possible - and reasonable - near the point where
the data originates. The results are then transmitted to the next higher
processing level, sometimes over significant physical distance. However,
long distance transmission is not an element in the basic concept of
distributed processing. Thus, the principle of distributed processing
could apply in photogrammetry to individual pieces of equipment, or to
the entire photogrammetric data processing system.
Multiprocessor systems, organized in nets, fans, rings, or other
configurations and operating in parallel or serial fashion distribute
processing resources by task rather than location. In a wider sense, *
they are also examples of distributed processing. Such use presently
involves mostly minicomputers. However, the availability of inexpensive
microprocessors has opened entirely new vistas for distributed processing
of this type. Because the technology is still very young, it has several
obstacles to overcome before its promise will be fully realized. Com
munication among multiple processors will probably turn out to be one
of the main obstacles, particularly when the data transfer rates are
high. [10j, [11]
Photogrammetric equipment we are all familiar with contains a spec
trum of digital elements. These range from simple encoders and counters
of coordinate recorders to fairly sophisticated computer control of analy
tical plotters. [12] Beyond that, advanced systems, such as the Epipolar
Scan Stereomapper [13] extend the spectrum into high speed parallel pro
cessing and operation of multiple processors in a real-time environment.
As promised earlier, we will now explore the trends - realized or
realizable - in the development of that spectrum.