25 
plotters which tend to be replaced partly by the fully-digital-type plotters 
and partly by the computer-supported-topographic plotters. The latter might 
be modified or adapted to optimal operation. 
The equipment components are being designed modularly and fitted 
for on-line and off-line operation. An important consideration is compatibility 
of modules. 
Though the role of minicomputers will be significant in the future 
systems, microcomputers are gaining in importance. They cost less, are 
flexible and usually fast enough. However, the development cost, in order 
to make a system including a microcomputer operational, should not be 
underestimated. 
For efficient operation well designed keyboards and alphanumerical 
and graphical display terminals are essential. In order to achieve high versa- 
tility different peripheral units should be provided. 
Equipment and the corresponding software are highly related. The 
present trend is to shift the emphasis from hardware to software develop- 
ment. In the near future a rapid qualitative and quantitative growth of soft- 
ware may be expected. New application programmes will be developed, part- 
ly by the users themselves. 
The interactivity level between analogue and digital components tends 
to increase. The flow of information between these components can be uni- 
directional (in serial systems) or bi-directional (in closed loop systems). Bi- 
directional flow can raise the system’s capabilities substantially. 
Several computer supported instruments can be bundled in a multiple 
system. They have a central (mini-) computer in common which can be 
linked with the individual (sub-) systems serially or in closed loops. The 
latter, implying a distributive computer network, are more flexible and 
versatile than serial systems. Some operations can be performed semi-auto- 
matically (e.g. orientation) and acquisition of new data can be adapted to the 
previously given data. 
In automated systems a computer may also support automatic scanners/ 
sensors, correlators and control agents. 
Another important property is selfcalibration capability. Selfcalibration 
can be applied to the locations of projection centres, to different orientation 
parameters and to instrumental deterministic errors.