1 
Photogrammetria, XIX, No. 6 
electrical signals in his nerves and brain, to the elementary motions (dynamic signals) of 
the operator’s hands, driving mechanism, scanning device in the projection, parts of the 
projection system, and the scanning device of the photograph. The output signals of the 
feedback loop are the input signals for the open loop system, which contains all the com 
ponents between the scanning device of the photograph and the top of the tracing style 
(fig. 4), where the output is recorded. 
In the illustrated case the feedback loop and the open loop systems are partially 
overlapping. 
The dynamic signals are recorded as line elements (symbols), connected into continuous 
figures (messages). 
For a more accurate evaluation, the output may be recorded in an enlarged scale (by 
special means). 
In monocular plotting the relationship between the input and output is linear if the 
system-parameters have been selected accordingly (zero tilts). 
III. 2. Approach of the method. 
Fig. 4. indicates the main sources of disturbances and the grouping of them. For 
this purpose the process of information flow and disturbances involved must be studied 
thoroughly. The latter should be classified into groups with similar effects on the output. 
It is convenient to form a minimum number of distinct groups of disturbances, which 
are sufficiently representative of the system-performance. 
The following classification is suitable for the case under consideration: 
1. Stochastical disturbances: 
a. uncertainty in the visual perception and interpretation: X 
b. sensitivity of the scanning mechanism in the projection: l 
(including the friction, inertia, mass etc. related to the plotting speed and the 
operator’s reacting ability), 
c. those originating in the plotting device: L 
(e.g. dry friction, etc.).