3 
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. 
TRENDS IN DETAIL DESIGN 
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