Dorffner, Lionel
The production of the orthophotos was also done using
a software program developed in Vienna . In contrast
to conventional 2.5D orthophoto software, this
program operates on a full 3D data base and allows any
arbitrary spatial position of the orthophoto image
plane. The definition of the orthophoto planes was
done by approximating the visible part of the dome by
a polyhedron (Figure 5). The projection itself was
performed orthogonal on to the facets of the
polyhedron. For each of the 59 facets one orthophoto
was computed for an output scale of 1:25.
Figure 5. polyhedron used for orthophoto production
6 VISUALIZATION AND INFORMATION SYSTEM
For visualization a 3D photo-model was generated and stored using the data format VRML. VRML is an acronym for
"Virtual Reality Modeling Language". It is the international standard 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, platform independent language for publishing 3D Web pages. Using this possibility of making
VRML worlds available over the internet a great public can access this kind of 3D information.
To be able to view such a 3D scenes a VRML-Viewer is necessary. This viewer can either be a standalone program or it
can be integrated as a plug-in into a HTML-Browser. There are a lot of such viewers on the market for every current
operating system. Because most VRML viewers are available free no additional costs arise for the viewing software.
Within such a scene the user can interactively move around and examine the virtual world (Figure 6). Of course some
viewpoints and key-positions can be defined and then an automatic flight through the scene can be animated in real-time.
By using VRML additional information apart from geometry and texture can be linked to the 3D model. This
information can be in the form of text documents, sound sequences, movies or even other VRML scenes. All aspects of
virtual world display, interaction and internetworking can be specified using VRML. Using these possibilities 3D photo-
models combined with VRML technology have a very broad applicability as for example distributed visualizations,
interactive environments, interactive simulations for education, virtual museums, and more.
Figure 6. Visualization of the photo-model using the VRML viewer CosmoPlayer
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 177
