values are photoelectrically scanned in the correct correlation of x, y and z in the control unit Ph. 
This process of automatic readout and the respective exposure takes about two hours per model. 
As compared to the “direct method”, the “storage method” offers the following advantages: 
a) Plotting instrument and Orthoprojector may be operated at different speeds. 
B 
Fig. 5 Operation of Orthoprojector by "storage method”. 
b) Erroneous measurements can be erased in the store and repeated without destroying all pre 
vious measurements. 
c) In the control unit, additional information can be taken over from the store, so that, for example, 
the so-called mismatches caused by residual errors of measurement and the slope of the terrain 
can be reduced by “interpolation processes”. 
d) Several plotters with store can be used to drive, one GZ 1 instrument, since more time is re 
quired for measurement than for exposure. 
e) If re-flights are made years later, for instance for map revision, the respective storage plates 
can be reused, provided that the flights are designed accordingly. 
These advantages are obtained by a certain increase in the instrumental means employed. Figure 2 
shows at the right, beside the Orthoprojector proper, the control unit used in the storage method. 
Fig. 6 C 8 Stereoplanigraph with coupled storage device for recording of terrain profiles. The operator controls 
only the z-drive, while x and y are fed automatically. The knob v serves to select the traveling speed in 
y-direction.