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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