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laser scanning for elevation measurement and airborne video
for thematic data in time. The laser scanning is to replace the
traditional photogrammetric approach to obtain profiles of the
beach and foredunes (see figure 3 and 4). These techniques
seem to be much more promising for these kind of areas then
digital photogrammetry: the lack of texture doesn't influence
the accuracy of laseraltimetry data badly, and the little objects
to be gathered by vectors won't need high precision images like
(scanned) photographs.
As of 1996, a DEM of the beach and foredunes of the Dutch
coast will be provided annually, based on laser scanning data.
Also, once every year the complete coastal zone (incorporating
dunes) will be surveyed. Video data will provide information
on e.g. vegetative cover, development and migration of blow-
outs. In addition, by means of bird's-eye-views a good visual
impression of the coastal area is obtained (Huising and
Vaessen, 1996).
4.2.3 Road network database The appearance of the final
product 'road network database' is mostly as desired by the
users. À major problem is to keep this database up-to-date, i.e.
all roads and existing streets are present in the database, and
streets and roads which are changed in position, are moved in
the database.
Photogrammetry could be a suitable technique for updating the
database, in particular digital photogrammetry giving the
opportunity to use low-cost pc-systems in stead of expensive
analytical plotters or analogue stereoscopes.
During 1994 and 1995 we carried out a test using our pc-
mapping system DVP of Leica, and scanned aerial photographs
scale 1:18.000. This small scale basis product accompanied
with a comparative low-accuracy mapping system, delivered a
relatively cheap update process; the human power costs are
about $ 0.6 million and the costs for the instruments used are
about $ 0.05 million (Wicherson and Van der Kraan, 1995).
4.3 Future expectations
At this moment at least two other topics are in view for using
digital photogrammetry efficiently in the future: automatic
2.
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Figure 3: Beach profile, as currently produced
aerotriangulation, substituting semi-automatic aerotriangulation
performed on the DCCS, and generating vegetation maps
digitally.
4.3.1 Automatic aerotriangulation Many reports that have
been published during the last years give an optimistic prospect
of the operational use of automatic aerotriangulation, see for
example (Tang and Heipke, 1996). The DPW-770 of Leica
provides a module for automatic aerotriangulation. We tested
this module extensively during our benchmark in 1995, and the
earliest results were promising indeed. Subsequently we will
carry out extended tests in 1996, and if these tests bear out our
careful optimism, we can substitute the DCCS by a stripped
version of the DPW-770, embodying only the most necessary
modules for automatic aerotriangulation.
4.3.2 Digital vegetation maps As described in chapter 2, the
vegetation maps are only available in digital format at the very
end of the process. This mainly analogue process can be sub-
stituted by a digital-photogrammetrical process, probably with
rather much profit.
The idea is to scan false colour photographs and to use a pc-
based photogrammetric mapping system, like our DVP.
Advantages of using digital images and techniques above our
current process using analogue images and techniques, are the
possibilities to use old vector maps for superimposing purposes
and to fasten up the internal process by removing the stage of
scanning, skelettonizing, vectorising and correcting the vector
map. Moreover the possibility arises to quantify vegetation
types by using (semi-)automatic multi-spectral classification as
an extra product.
Despite these advantages, we still don't use digital photo-
grammetry because of some technical problems (huge storage
capacities needed) and other organising aspects, like starting
problems resulting in loss of production, and minor importance
given to implement this technique in our production
environment at the moment.
Figure 4: Laseraltimetry DEM of a part of Ameland, heights are
represented in grey values.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996