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The principal approach to this new possibility is offered by VRML language, which has been
proposed in 1994 by Mark Pesce (Pesce. 1995), and which has been subsequently developed by
many research and commercial centres, giving rise to a complete and powerful language to
describe 3d data sets and to support interactive navigation in such environments.
The kind of navigation which is supported by VRML language is. first of all, the visual
navigation by moving a virtual camera in the three dimensional scenario. But more powerful is the
possibility to enrich a 3d model as an hypertext, by adopting the HTTP standard which is
supported by all Web navigation browsers. Therefore a VRML based navigation browser can be
activated by a Web browser, and connecting URL links to relevant parts of the 3d model makes
possible to get back the required Web page. The adoption of this methods, standards and tools
opens up the possibility of creating a distributed environment to support co-operation among
researchers in the field of earth research.
The approach that we adopt to the development of a virtual environment for earth landscape
analysis and navigation is base on the following main stages: first of all a DEM is constructed by
interpolation methods; the DEM model is subsequently enriched with colour rendering parameters
derived from analysis of satellite images; the rendering of the DEM is performed so that a
perspective projection with moving camera position can be generated; a variety of analysis tools
can be furtherly applied to generate different views of relevant parameters.
All the above mentioned stages can be performed using the interactive system TISS,
which, moreover allows us to create animation sequences that can be coded into standard video
files that can be played inside TISS or by using Mpeg or Quicktime plaversc (Mpeg and Quicktime
are standard methods to code an image video sequence).
To further extend the level of interactivity with the reconstructed landscape, we have also
implemented a simple program that converts the DEM data structure into the standard VRML
representation. This recently standardised 3D description and modelling language is the best
environment to insert into the landscape model other data, creating, for example. 3D tematic maps,
or integrating man-made buildings coded as geometric models.
The system is based on a set of modules that allow us to:
- reconstruct the Digital Terrain Model (DEM) by adopting a variety of interpolation
techniques (kriging and fractal fBM),
- to associate to each element (pixel ) of the terrain model a colour code which corresponds
to the spectral reflectance of the earth sampled area.
- to generate Photorealistic rendering of the reconstructed DEM with their proper colour
codes and by simulating different illumination conditions.
- to navigate interactively in the reconstructed and rendered landscape.
- to display a navigation sequence pre-determined along an exploration path, producing an
image sequence like a movie film.
2.0 MODELLING THE EARTH LANDSCAPE
In order to make a Virtual Reality model of the Earth landscape, a fundamental step is the
reconstruction of a three dimensional geometric model of the real world, both natural objects such