Hempenius, Makarovid, Van der Weele, Tests of Restitution Instruments 
The quality of contour lines and restitution by points lie out of the scope of this 
analysis. The former is influenced by other non-dynamic phenomenae (e.g. slope) while 
the latter are static operations. The flow of information (or process) passes two main 
parts of the channel (plotting system): the dynamic and non-dynamic part. 
The channel consists of the closed loop system (or the feedback loop) and the open 
loop system (fig. 3). The signals in the feedback loop change the form from the light 
intensity variations between the photograph and the retina of the operator’s eye, via the 
Fig. 3. Functional block diagram of the information flow in conventional photogrammetric 
plotters with a movable observation system. 
Legend: double boxes indicate the input and the output, single boxes represent the com 
ponents of the plotting system, dotted boxes indicate the process and the corresponding 
signals in it.