20 
c) . Observation system» 
Fixed horizontal photo-planes enable the employment of a fixed comparator type ob 
servation system. Light sources are provided for the observation of transparences and 
paper prints. The measuring marks are luminous dots with adjustable intensity. The 
magnification is x6 and the field of view is 40 mm. 
d) . Tracking and measuring device. 
As driving agent for planimetrie motions, a sphere is employed, supported by an arm, 
mobile on cross-slides. The operator rolles the sphere over a plane friction surface. 
The displacements of the X- and Y-slides are transferred via mechanical links twice 
reduced to the projection system. These motions are also transferred to the plotting 
device - the transmission ratio to the latter can be changed continuously. The plani 
metrie coordinates cannot be measured. 
For tracking in height (Z), a hand wheel is provided. The height measurements are 
performed by means of a drum with masks and a setting knob (for gears) for changing 
the scale. 
For plotting of profiles, the sphere (for tracking) has to be replaced by a pin, which can 
glide along a groove on a rail fixed on the tracking surface. The rail is located and orien 
ted along the desired profile. On the drawing table, one of the coordinate carriages must 
be connected to the Z-drive. 
e) . Plotting device. 
The drawing table, located at the left on the top of the instrument, is slightly inclined 
towards the operator. The X- and Y-carriages of the plotting device are coupled with 
the corresponding carriages of the tracking device by means of mechanical proportion 
links. The transmission ratio can be changed continuously between 2:5 and 5:2. The 
guides of the coordinate carriages of the plotting device are provided with lead screws 
(which are normally not used). For plotting of profiles, one of the carriages must be 
disconnected from the proportion link (tracking device) and connected via the lead screw 
to the Z-drive. 
The size of the drawing surface is 500x500mm. 
III. 7 Medium Scale Plotter-G . S . I, (Geographic Survey Institute - Tokyo), 
a). General. 
The instrument has been developed for plotting of topographic maps in scale 1:25.000 
from 9" x 9" wide angle near vertical photographs. The construction is compact and 
to some extent similar to that of the Stereograph-Drobyshev. 
The principle of the projection system is well suited for affine restitution, although 
it has not been designed for this purpose. 
The main parts of the instrument are: the projection system, the observation system, 
the tracking device (for model space), and the plotting device.