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Title
International cooperation and technology transfer
Author
Fras, Mojca Kosmatin

52
together with an orthophoto as texture source more
than 99 percent of the data is needed to store photo
texture in an uncompressed way. Experiments
prove that lossy compression techniques, such as
JPEG, shrink the original texture files to some 5
percent of its former size without significant loss of
quality.
Although uncompressed during visualization the
texture can be stored in small files thus enabling
faster loading from disk. Decompression in memory
is much faster than disk reading. The resulting loss
of information and accuracy is acceptable, as the
images are used mainly for visualization and
animation purposes.
3 IMPLEMENTATION
More than 25 years ago a modular program system
(SCOP) for the generation and management of
high-quality DTM data with a hybrid data structure
was developed at our institute in Vienna (Institute of
Photogrammetry and Remote Sensing
[http://www.ipf.tuwien.ac.at]) in very close cooperation
with INPHO GmbH in Stuttgart (Germany)
[http://www.inpho.de/scop.htm]. In the course of the
years the functionality of SCOP has continuously
been extended and improved.
The DTM is integrated in SCOP as the central data
base, and so it is possible to derive in a very flexible
way (using additional modules) numerous follow-up
products. Some important modules are:
ISOLINES (derives isolines from any digital
surface described in the data structure of
SCOP, this can be elevation models, slope
models or difference models)
DOP (generation of digital orthophotos based
on the high quality DTM data structure)
PERSPECT (produces static 3D views of the
DTM in form of a perspective representation or
a parallel projection)
PROFILE (interpolates single heights and height
profiles - longitudinal, parallel, cross-sections -
for any polygon position within the DTM area)
TDM (management and archiving of huge
amounts of terrain data using a relational data
base system with efficient geometric queries)
As a consequence of the increasing demand for
interactive visualization an additional module to
SCOP has been developed and implemented. This
new Animated Terrain Model (ATM) tool provides an
easy way for preparing and exporting SCOP DTM
data for interactive 3D visualization.
If the exported area is also covered - maybe only
partly - by an orthophoto or an orthophoto mosaic
this image data can be mapped as texture
information over the animated terrain model. Areas
without texture information are visualized as gray
shading. In addition the predefinition of viewpoints
and even a whole camera path for an automatic
flight through the model can be done graphically in
ATM (Figure 2).
Figure 2 User interface of ATM showing coded DTM
and defined flight path.
The data is then exported using the data format
VRML97. VRML is an acronym for "Virtual Reality
Modeling Language". It is the international standard
(ISO/IEC 14772) file format for describing interactive
3D worlds and objects on the Internet [Carey R.,
Bell G., 1997]. It is in fact the 3D analogy to HTML.
This means that VRML serves as a simple, multi
platform language for publishing 3D Web pages.
For visualizing such data a VRML viewer is
necessary. This viewer can either be a standalone
program or it can be integrated as plug-in into a
HTML browser. There are a lot of such viewers on
the market (CosmoPlayer™, CASUSPresenter™,
VRwave™, WorldView , ...) for every current
operating system, most of them as freeware [The
VRML Repository]. Therefore, no additional cost
may arise for the final user. The VRML world
enables the users to interactively examine and
visualize their data.
As this data format is used on the Internet it is
basically designed for a small amount of data.
Therefore, special attention has been given to
managing large data set, that have to be dealt with if
DTMs or orthophotos are examined and visualized
interactively. In order to achieve this goal all
requirements for efficient visualization mentioned
above have been realized in ATM.
The whole DTM model is split up into Tiles, each
one stored in different levels of detail. The image
pyramid of the orthophoto is also divided using the
same Tile limits. The number of grid points and the
number of pixels within one Tile as well as the
degree of data reduction for the LODs can be set by