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ANALOG OR DIGITAL MAPPING FROM AERIAL PHOTOGRAPHS ?
A Contribution to the Conception of Digital Mapping Systems
0. Kòlbl
Ecole polytechnique fédérale de Lausanne
Photogrammétrie, GR-Ecublens, 1015 Lausanne / Switzerland
Summary
Digital methods offer great flexibility for image processing; however, for visual
measurements, these techniques do not enable one to obtain performances simi
lar to those achieved by analog means for image presentation. Consequently,
digital mapping is preferable for largely automated operations like image
enhancement, the derivation of digital terrain models or the production of ortho
photos, whereas digital instruments do not currently provide performance
comparable to good analytical plotters.
New procedures will be added to the current photogrammétrie activities, like the
use of aerial photographs in geographic information systems or the reproduction
of maps based on pictorial information. This will result in instruments made up
of components such as : scanners, parallel processors, geographic information
systems with underlayed aerial photographs, stereoscopic measuring instru
ments and electrostatic plotters.
The author anticipates this evolution of photogrammétrie instruments, based on
his own experience, consisting mainly in the development of a system for the
automatic derivation of digital terrain models, including a high-speed processor
based on Transputer technology.
Keywords : Digital photogrammetry, Digital terrain models, Image processing,
Instruments, Land information systems, Photogrammetry
1 . Introduction
During the last few years, photogrammetry has drastically changed. The classi
cal procedures for image measurements on analog instruments are gradually
being replaced by analytical techniques and already partly by digital methods. For
sure, this development has not yet reached its final stage and more and more
interesting possibilities are arising concerning the automatization of image proc
essing and data management in information systems. In particular, the inter
relation between a photogrammetric plotter and an information system requires
good facilities for dialogue between the plotter and the database.
Most of the recent realizations depend on the progress in electronic data process
ing, and the desired speed and efficiency of computer processors is as yet only
partially available. A good part of this paper deals with future developments and
it is always a bit hazardous to extrapolate too far, as there is a risk of overesti
mating technological progress. The author, conscious of this danger, has tried to
