- Databases management -
VWorldTerrain
technology is based on a principle of generation of geometry in real-time.
In order to achieve that, we have to apply data (x, y, z coordinates) to the
math equations which define the terrain rendering. These data are either:
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totally invented, as it the case for modeling, - or come from existing models, which are Digital Elevation Models (DEMs). |
Indeed, in order to achieve
a high degree of realism, especially when we come to projects which are based
on real world locations with real data, we use existing models.
Three types of data are in fact used:
-DEMs
(Digital Elevation Models), so as define topography (altitude) -Satellite imagery, so as to display the right colors. -Information on the type of ground and vegetation cover. |
1) Digital Elevation Models ( DEMs):
There are several types of DEMs, in terms of precision and according
to the various ways they can be obtained, namely from:
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geographical maps: use of contour lines - stereoscopic aerial pictures, so as to infer the corresponding ground relief - radar measures: made most of the time by satellites or space probes. |
In any case, those data are processed to make 3D terrain digital files, in which x and y generally express geographical coordinates (latitude, longitude) and z (altitude, in meters).
E.g.:
The Earth model we used for Eingana:
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GTopo 30 (USGS) data, x, y precision = 1km, vertical precision = 1m ( i.e.42 000 kms x 21 000 kms)
Marineris Valley (Mars) model:
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MOLA space
probe( NASA) data, x, y precision = 463 m, vertical precision = 1m
(i.e.2 000 kms x 1 000 kms).
Mount Saint Helens model:
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SDTS (USGS) data, x,
y precision = 10 m, vertical precision = 0,1m
(i.e.30 kms x 30 kms).
Those files are represented
by more or less large squares, depending on how much precise they are; they
have to be assembled according to the desired surface area.
It is therefore by interpreting these altimetric coordinates in real-time that
VWorldTerrain
is able to display simultaneously the desired environment’s topography.
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2) Satellite imagery:
After having recreated topography by linking up each point (altitude), we have
to apply realistic texture mapping to geometry.
The use of satellite pictures is of great help to achieve a realistic mapping,
since these are vertical pictures of the ground.
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There are various types
of satellites, but the ones used for imagery are observation ones.They are about
800 kms above the Earth and possess a heliosynchronous orbit, which means these
satellites are always in line with the Earth and the Sun and take pictures at
fixed times, with their back to the Sun.
These are 180 x 180 kms pictures. They contain various layers of information:
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3 RGB (red, green, blue) channels, which represent the visible channels
of the light spectrum. - 4 infrared channels (for remote-sensing: water, vegetation…) |
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Unprocessed image
By mixing these RGB channels, we obtain the true colours of the original picture.
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3) Information on the nature of the ground and vegetation:
These data are provided
by the satellite pictures infrared channels.
Indeed, after analysing and combining these channels, we can infer missing data
on lakes and river network, vegetation cover, etc ….
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This research work, called remote-sensing, with a joint research job out in the field, along with a very precise classification, results in the reproducing of the exact nature of the terrain with the corresponding vegetation, at the appropriate location.
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Therefore using and processing those three types of data in real-time is the key to the three-dimensional reconstitution of the universe accomplished by VWorldTerrain, with such an amazing realism.
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