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The role of digital components in photogrammetric instrumentations

follow each other at two to three year intervals. This contrasts drasti
cally with the traditional ten to twenty year cycle of photogrammetric
equipment. The objective of this paper is to identify trends in the
design of digital components for ph<>;ogrammetric equipment, and to show
where such trends may lead when extended on the basis of developments in
digital technology.
In discussing the trends in the design of digital equipment for
photogrammetric instruments, it is not practical, nor necessary to attempt
to cover its entire scope. Some illustrative examples, such as coordinate
recorders, servos, and analytical plotters give clear indications about
the trends and their extensions on the basis of developments in general
digital design. These examples will be discussed later in this paper.
However, before that we must digress a little and have a look at digital
design trends in the wide world outside photogrammetry.
Detail design of digital electronic devices, including those likely
to find use as components of photogrammetric instruments and systems, has
an overwhelming trend toward integration. The technology has evolved
very rapidly from the discrete component level to medium scale integra
tion (MSI) and from there to large scale integration (LSI). Lately,
concepts like giant scale integration (GSI) and very large scale inte
gration (VLSI) have appeared in the literature. Another way to describe
this evolution is to say that the device complexity has progressed from
a few active elements (such as transistors) per device to. thousands of
elements (LSI) and is on its way toward hundreds of thousands of elements
per device.
Associated with increasing device complexity is a dramatic reduction
in the cost of active and passive elements. Decreasing cost of elements
leads to a parallel reduction of cost per function. Thus, the cost of
equivalent computer power, as an example, has decreased, and keeps de
creasing by one half approximately every two years. Similar reductions
in the cost of digital functions performed digitally are observable
throughout the industry, but are more difficult to quantify because
there is no stable comparison base.
The integration trend poses problems for the designer. First the
technology is very complex and specialized. Very expensive manufacturing
facilities are needed, and the realization of designs requires that numer
ous rules and constraints be meticulously followed. Second, full cost
advantages accrue only when the device is manufactured in very large
quantities. When only a few devices of special design are produced, the
cost per device is very expensive indeed. The design responsibility has
been shifting to the semiconductor manufacturer, who designs and produces
functionally defined devices, expected to find wide acceptance and use