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and information systems, for which an important part of the work is executed on
the monitor with the displayed map information. However, a line map is very
abstract and can lead to errors, especially if the map information is incomplete
and not updated. The incorporation of aerial or even terrestrial photographs dis
played together with the line map might be very helpful.
Intergraph and Siemens (Sicad) have already developed such information sys
tems with the possibility of image underlaying, in which the aerial photographs
are shown on the monitor. By using orthophotos, it is possible to create a geo
metric reference which can also be used for the data updating in the information
system. Of course, this image underlaying requires the digitalization of the aerial
photographs.
6 . Complex digital mapping systems
It can be deduced from these various aspects that digital image processing will
considerably change the whole mapping process based on aerial photographs.
But in a similar way to the analytical plotter, which not only took over the func
tionality of an analog plotter but also induced new possibilities, digital mapping
will also open new perspectives. However, the result should no longer consist in
one unique standard instrument, but rather in a series of components which can
be combined to make up a system. Such a system could be composed of the follow
ing elements :
scanner for the transformation of a photogrammetric analog image into digi
tal form
image memory of several gygabites for the storage of image information, most
probably in connection with optical discs
image composer, image processor with monitor for grey-tone adaptation and
the assembly of images as well as for the mounting of letterings
parallel processor for the automatic derivation of a digital terrain model and
the elaboration of orthophotos or landscape models, but also for tasks like
automatic aerial triangulation
geographic information system with underlayed aerial photographs
(monoplotter)
stereoscopic measuring instrument (digital or analytical) with image injection
for the verification of the results of the automatic plotting and for visual
restitution
electrostatic plotter for the production of half-tone images and line maps
photographic image recorder for the reproduction of high-quality printing
masks
This list may be incomplete, but it shows that the stereoscopic plotter will no
longer play the central role it still assumes today. Numerous processes, such as
for instance image matching, might be done completely automatically, without
supervision. For computations, efficient processors - most probably parallel pro
cessors - will be required, such as the Transputer array, currently developed at
the Institute of Photogrammetry for image correlation. Such processors could
also be used for other computer-intensive operations like the management of a
database for geographic information systems.
