(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.