(10)
of the plotting machine and the sensing and control equipment.
In Section 2 it has been suggested that the intrinsic character-
istics of available servomotors are sufficiently good to achieve plot-
ting speeds with mechanical plotters that are orders of magnitude higher
than the human operator can consistently achieve over long periods.
These
speeds are available if the torques of the servomotors can be controlled
in an optimum manner.
However, it is clear that the most desirable type
of machine is that which involves the positioning of the smallest masses
with the simplest possible mechanical linkages.
Vibration and wear in
mechanical parts affect not only the accuracy of plotting but also
geriously degrade the performance of feedback control systems.
backlash is particularly serious.
Mechanical
The use of computers to provide
analytical modelling in plotters and hence to replace mechanical linkages
is most desirable.
In Section 3 it has been shown that the control of servomotor
torques by automatic feedback control systems is complicated by measure-
ment noise and by the intrinsic variation of the parameters that relate
these torques to information bearing signals.
The performance of the control systems is strongly dependent on
the characteristics of the terrain being mapped and on the image char-
acteristics of the photographs.
if optimum performance is to be achieved.
Adaptive control systems are essential
The most effective automatic plotting machine will be one that
has highly adaptive control systems and in which functions of photo-
gremmetric modelling, scanning and tracking are effected as far as
possible by electrical means using computers and electronic circuits.
Hobrough's
necessary to achieve high performance.
machine displeys many aspects of the adaptive techniques
Helava's analytical plotter
indicates an approach to the replacing of mechanical linkages by com-
puter simulation.