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(b) Geometrical__£)re : processing of SPOT imagery
Images which will be sent by the SPOT satellite (schedu
led to be launched in 1984) will have to be geometrical
ly corrected. First level corrections will take into
account :
- earth rotation
- earth curva ture
- satellite altitude variations
- satellite velocity variations
- angle of view from the satellite.
At level II, control points will enable to rectify
vertical views.
At level III, D.T.M.'s will be used, together with
control points, to rectify both vertical and oblique
imagery. The precision that can be achieved thanks to
D.T.M.'s may enable to revise maps at scales lower than
or equal to 1:50 000 with SPOT imagery.
(c) Perspective views
The operator chooses the point of views and the pers
pective is plotted on a profile by profile basis, the
hidden points being got rid of.These perspectives can
be useful to planers, geologists and geomorphologists ; ;
they also serve a teaching purpose (the image of the
terrain can be very easily interpreted), and are used
at IGN-Fasa control.
D.T.M. - DERIVED CARTOGRAPHIC OUTPUTS
(a) Slope and slope orientation maps
The terrain slope is computed for each D.T.M. grid element.
Slope and slope orientation maps can therefore be pro
duced which are helpful for solving problems linked with
planning and agriculture. Graphic output equipment used
includes a high speed colour plotter which produces an
easy-to-read document, and a film raster plotter.
(b ) Insolation maps
Calculation takes into account not only terrain slope and
orientation, and the cast shadows produced by the surroun
ding relief, but also absorption factors according to the
elevation of the sun and to the altitude of the point. It
is expected to use simultaneously a model of nebulosity.
Graphic outputs are of the same kind as those used for
si ope maps .
(c ) Intervisibility maps
It is determined the set of all points which are visible
either from a given point of view, by an observer being at
a given altitude, or from several points of view.
This kind of map concerns mainly regional planners, with
the framework of respecting the visual environment (choice