2.- Guiding the floating mark - The terrain carriage and thus the floating mark are guided free- 
handedly. The carriage runs on a compound-slide system roughly at the level of the rugged base 
frame and also at the level of the two space points. The result of this arrangement is high hori- 
zontal-position accuracy with a point error of about 20 um as referred to the photograph. 
The carriage runs on rollers on the rails. The wide separation between these rollers guaran- 
tees proper parallel guiding and prevents any rotation of the carriage. 
The terrain carriage is suspended in the guide system and does not stand on the internal tra- 
cing table. This leaves a few millimeters' space between the manuscript and the terrain carriage. 
The carriage will thus neither damage nor degrade the manuscript by its motion. 
A system of counterweights greatly facilitates the operator's work, causing only minimum 
residual forces act on the terrain carriage. As a result, the floating mark can be smoothly and 
accurately guided along terrain features. 
3. - Internal tracing table - The internal tracing table has a useful drawing surface of 68 x 40 cm2. 
Here also there is enough room for accommodating overhanging parts of the manuscript so that 
they will not obstruct the work. The table is of the luminous type. 
4.- Viewing - Right angle viewing and a fixed optical system guarantee high viewing quality. Ey- 
piece magnification is 6 x. The optical system of the Planitop has no moving parts. 
9.- Tracing device - For the Planitop also, tracing tools are available for a wide range of diffe- 
rent techniques : pencil, ball pen, ink-pen holder and scribing tools. 
6.- Digitization - The Planitop is likewise suitable for digitization. Linear encoders are used for 
the horizontal coordinates and rotary encoder for elevation. An Ecomat-11 recording unit serves 
for coordinate display and output. 
Practical work 
In the following a few examples are given on mapping and map revision done with Plani- 
cart and Planitop. 
1.- Revision of 1:5 000 and 1:25 000 maps in Germany. 
The Topographic survey at Bad Godesberg is using the Planicart to revise maps of 1:5 000 and 
1:25 000 scale. The instrument has given excellent results. All the work was performed on the 
internal tracing table. 
The different operations in the Planicart were the following : 
a) Relative and sufficiently accurate absolute orientation. 
b) Sectional exploration of model and map sheet for changes. 
) Partial positioning of model in relation to fixed map sheet. 
) Plotting of outlines of new features. 
) Graphical completion and treatment. Moving the y-carriage after disengaging it in 
y was found of advantage for this operation. 
c 
d 
e 
The 1:5 000 map was revised on the basis of air photos of 1:13 000 scale. Two and a half days 
were needed for one map sheet (two models). 
The 1:25 000 map was revised on the basis of air photos of 1:64 000 scale. Here, 13.5 days 
were required per map sheet (two models). 
The Topographic Survey of Bad Godesberg also tested the Planitop for revising its 1:25 000 
map. This work was based on 1:32 000 photography. This was directly plotted on the internal tra- 
cing table at the 1:25 000 map scale. The results were very satisfactory. They were compared 
with a Planicart plot of the same map sheet and showed very good agreement. The differences 
found were due to differences of interpretation explained by variations in model scale (1:10 000 
was used in the Planicart). 
2. - Mapping in 1:1 250, 1:2500 and 1:10 000 scales in England. A further example for graphical 
plotting with the Planicart is his use by the British Ordnance Survey. Here all the possibilities 
of the Planicart are used : Restitution with the focal-lengths 305 mm, 153 mm and 85 mm and 
plotting on the internal and the external table. 
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