21
Special Publication reprinted from:
Nachrichten aus dem Karten- und Vermessungswesen
Reihe II: Deutsche Beiträge in fremden Sprachen — Heft Nr. 18
Verlag des Instituts für Angewandte Geodäsie, Frankfurt a. M.
An Auxiliary Instrument for the Revision of Maps and Quick
Preparation of Cadastral Maps and Other Large-Scale Plans
By Erwin Gigas, Frankfurt a. M.
This article has been published in German in the publications of the “Nachrichten aus dem Karten-
und Vermessungswesen — Reihe I/Heft Nr. 30“.
A problem of decisive importance in cartography is the revision of maps. At the
present stage of technical progress the map details (construction and displacement of
roads, construction of settlements, expansion of towns, construction of bridges and
canals etc.) are subject to such a frequent and varied modification, that a topographic
map is out of date and obsolete already within a few years. The so far used procedure
of collecting informations in Construction services, Road administrations etc. is ad
vantageous because of its cheapness, but it is time-consuming. These informations,
frequently not distinguishing between “completed“ and “planned“, require a detailed
checking in the field, mostly a topographic supplementary survey is also indispensable.
Therefore it suggested itself to make use of aerial photographs, as obtained from
regularly systematic photo flights, for this purpose. Aerial photographs give reliable
information and show all.topographic modifications, no matter whether completed or
under construction. It is a well-known graphical method to transfer these informations
into a map, but this method has the disadvantage, that considerable time is required,
and that always a control is necessary which is mostly as time-consuming as the
graphical process itself. If we now succeed in transforming in a simple manner the
perspective projection into an orthogonal projection, then revision work could be re
duced to a minimum. An aerial photograph, rectified in this way, can directly be printed
onto a culture negative, on which places to be changed have been opaqued, or may be
laid under the negative for tracing. Then the cartographer can scribe the new map
details on the coated foil to show the present state.
The differential rectification is suitably made either by a linear profile scanning
of the model (see e. g. Ahrend, Brucklacher, Meier, Utz: „Der Orthoprojektor Gigas-
Zeiss“. — Bildmess. u. Luftbildwes., Berlin 1964, 3, pp. 153—160) or automatically by
means of a photo-electric automaton (Stereomat).
The differential rectification can be made fully automatically and the thus ob
tained information can always be used again for later photo flights, if instead of a
direct coupling a store unit is installed between the plotter and the Orthoprojector,
and thus the scanning is once made sheet by sheet. This procedure provides that
contour lines are unchanged, what generally is the rule, negligible modifications
excepted.
If we suppose that systematical photo flights are executed at 3—5 years intervals,
then the advantage of intercalating a store unit is evident. The store unit is also useful,
if several plotters are operated at different places, but differential rectification shall
only be performed with a centrally placed Orthoprojector.
Based upon these considerations and financed by the Deutsche Forsdiungsgemein-
schaft a first instrument of the Orthoprojector type was constructed for the Institut
für Angewandte Geodasie. This instrument has proved to be advantageous and suitable
also for other purposes.
