65 
DIGITIZATION OF RELIEF DATA AND EXPLOITATION 
OF DIGITAL TERRAIN MODELS AT I.G.N. (FRANCE) 
Antoine BERNARD 
Institut Géographique National France 
2 avenue Pasteur 
94160 Saint-Mandé - France 
The collection of digital geographical data, particularly 
relief data, is now being undertaken by the IGN in two dif 
ferent ways of digitization at medium scales. 
The first way processes existing topographic maps at 1:25000 
and works either by automatic lecture of contour lines 
sheets with an electro-optical scanner (then skeletonizing 
and vectorizing of the contours),or by manual following on 
conventional digitizer. In both cases an interactive proces 
sing on graphic working station (with color display) is used 
for editing and addition. 
The second way, by photogrammetry, is used for the mountai 
nous areas and is based on stereo-plotting from air-photos 
at 1:60000, then by adjustment and clipping of different 
models . 
Both types of data are stored in the same data base and are 
transformed into various products : 
. cartographic outputs of contour lines at different scales; 
. digital terrain models for various applications (ortho 
printing) ; 
. slope maps, perspectives, intervisibility maps, insolation 
maps etc . . . 
. processing of spatial imagery (corrections, classifica 
tions). 
In the future another way could be used after the launching 
ofSPOT satellite (1984), when stereoscopic images will beco 
me available at very small scales (1:400 000), providing 
through analytical stereo-plotting direct acquisition of 
altimetric data at 1:100 000.