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To measure areas from a map, there are three automated in
strument types at our disposal
a. Electro-planimeters
The outline of a parcel of land is traced by following it with a
magnifying glassthe area is registered on punched tape or punched
cards, and is at once available for further administrative or techni
cal processing by a computer. The Z 80 planimeter made by Zuse
and the Planimeter made by Stanley-Cintel belong to this class
of instrument. This type of instrument is less suitable for measuring
areas of quadrangular parcels.
b. Co-ordinate readers
There is a great variety of instruments within this class of which
I will mention only a few. In the first place the Polar Digimeter
made by Coradi, which is often wrongly called a planimeter because
of its appearance. The coordinates of the corner points defining a
land area are measured from which the area is derived by calculation.
Besides these there is a large range of co-ordinate readers capable
of measuring co-ordinates in a rectangular system. I mention a few
examples. In the first place the co-ordinate reader made by Benson
the reading area of this instrument is 50 x 70 cm. The points whose
co-ordinates are to be found are set by using a reading penwhen
the following system which operates under the working area reaches
one of these points registration is effected by pressing a button or
pedal. Because of its incremental motors it is possible that the
following system remains at a maximum distance of 0.05 mm in the
X and Y directions from the desired spot.
A co-ordinate reader resembling this instrument is the D-Mac
Pencil Follower. The reading area is 100 X 45 cm; the drafting
paper is placed on rolls.
Coradi has recently developed the Orthogonal Digimeter, avail
able in various sizes (from 80 x 80 cm up to 130 X 200 cm) and
designs. Its construction certainly allows accurate operation, but
does not permit quick operation.
For a similar development from Jena, I refer to [105].
N. V. Hagen Systems of Holland has recently developed its
HAROMAT Coordinate Reader. This instrument is available with
either 2 or 3 counting devices. It is provided with an effective area
of either 92 X 154 cm, or 117 X 154 cm. Its manner of construction
allows very quick operation. Recording of co-ordinates is possible
in any desired form: punched paper tape, punched cards,
magnetic tape, on-line with a computer. Interchangeable printed
circuits permit the use of any desired code. The recording system
of the instrument may also be coupled to all spindle equipped
photogrammetric restitution instruments. In this case, a third
counter is added. The operation board is not necessary in that case.
