20 
made between the single- and multiple systems; each of these categories can 
be classified further. 
2.1 Single systems (closed loop) 
Closed loop systems are still in the initial stage of development. There is, 
at present, one such system commercially available, i.e. the Real Time Position 
Analyser, developed by Xi Information Processing Systems Ltd, Israel (23). 
The system has been developed in two versions: RTPA2 (for two co-ordinate 
axes) and RTPA3 (for three axes). The corresponding configuration is shown 
in figure 7. 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
: Plotting Conventional Interface a-no.Display 
| Device Instrument Keyboard 
E a rm = addi 
| Control | Control I/O Units 
| Unit Eo Computer 
| Graphic | 
: Display | 
DL ZU 
figure 7 
configuration of RTPA system 
Experimental development has been carried out by Bendix (3), (4), the 
University of New Brunswick (UNB) (6), and ITC. In the following these 
experimental systems will be outlined. 
The Bendix Hybrid Plotter is a double projection type instrument 
(i.e. OMI Photomapper VI) supplemented by a digital computer. The basic 
components and their interactions are shown in figure 8. 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
OMI AN/UK-1 
Photomapper VI PTS Interface | Computer I/O Units 
Plotting Device Ejus | I 
Control 
Unit 
figure 8 
configuration of Bendix Hybrid Plotter