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Géoportail and 3D
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- Géoportail: start browsing in 3D
Géoportail: start browsing in 3D
A short, practical and entertaining introduction to three-dimensional cartography...
Before to start
First you have to download the 3D software (TerraExplorer) provided by Géoportail to your hard disk, then install it by unzipping it and clicking on the .exe box... Just a tiny effort before setting off on a fascinating flight into space.
At the controls
From outer space,
zoom in on the French region of your choice with the aid of the small virtual control in the top right of your computer screen - a graduated-scale cursor.
With it you can move up and down from a geostationary orbit thousands of kilometres above our planet, to... directly above your town, or even your own house! Above the cursor, a “joystick compass” lets you choose which way round you want to look at the map. In the bottom right-hand corner there is a small map of France, with a weather-vane shaped like an aeroplane indicating the compass point towards which the aerial view or map is oriented.
Heading south
For example, En Provence, you might choose to fly over the crescent-shape formed by Mont Ventoux, go back down to take a look at it in profile, go up again by clicking on the “See relief” icon, then leapfrog over the Pre-Alps to look at another crescent-shape, but this time the liquid one formed by Lake Geneva. Coming back towards Provence, you fly over some wooded areas and some urban areas dotted with turquoise blue flecks, which are in fact the swimming-pools in peoples’ gardens.
Between Carpentras and Avignon, you can see a number of large grey rectangles: these are the greenhouses where the famous aubergines, tomatoes and other vegetables of the Vaucluse region are grown.
Heading north
Now for a change of climate: go to the “Territories” section and select St-Pierre and Miquelon, off the coast of Newfoundland. You are now going to let Géoportail take you on a round-the-world voyage, hopping over the North Atlantic Ocean before re-entering the earth’s atmosphere just above this tiny string of French islands that tickles the edge of the vast lands of Canada. Zoom in on the town of Saint-Pierre and you’ll find yourself directly above the aerodrome, on the opposite side of the bay from the town. But it’s pretty cold in these parts, so you decide to set a course further south, towards the Antilles, then Polynesia, where you stay for a moment or two, before going on to hover above the volcano on Reunion Island... And that was your round-the-world voyage to the French overseas territories in relief!
Lexique
Altitude :
perpendicular height of a place above sea-level
Levelling:
technique for measuring differences in level so as to determine altitudes
Altimetry:
procédés de mesure et de représentation du relief d'un lieu ou d'une
région par l'établissement de courbes de niveau, de points côtés,
d'estompages, etc...
Contour line:
procedures for measuring and representing the relief of a site or region, by creating contour lines, spot heights, relief shading etc.
Digital Terrain Model (DTM):
portrayal of the shape of a site at ground level
Digital Elevation Model (DEM):
portrayal of the shape of a site at ground level and “above ground” features (buildings, forests etc.)
