REVISION DES CARTES 
MAPPING. WITH A FACET PLOTTER 
H. YZERMAN, Suisse 
The restitution of single photographs may be a more economical way of plotting, when suf- 
ficient control points are available. 
An aerial photograph contains the following geometrical displacements, as compared with a may 
1) Conformal distortions, due to difference of scale. 
2) Perspective distortions, due to the inclination between the photograph and the terrain surface. 
3) Affin distortions, due to the required orthogonal projection of sloping terrain. 
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It is important to verify, that perspective and affin distortions are of different origin, and 
require independent correction. Also the maps may differ in scale, projection and affin distortion, 
so that the same parameters may be used for their compensation. 
There is no stereoscopy during the plotting from single photographs, unless the map is an 
orthophoto. It is therefore recommended to prepare the photographs by : Pricking points under a 
stereoscope at ground positions of built-up structures and the control points, in order to avoid 
interpretation errors in the single photographs. Also : Working inside stereoscopically outlined 
terrain facets. 
The conformal, perspective and affin distortions can then be easily corrected for by means 
of geometrical optics. 
The photo scale is assumed to be in the practical range of 4/3 rd to 1/5th of the map scale, 
so that a conformal zoom for that range should be provided. 
The À Z of a terrain facet is assumed not to exceed 1/3rd of the average Z, so that a pers- 
pective scale variation of 1.4 in the field of view should be provided. This allows for an in inclination 
of about 20? between photograph and terrain facet. 
The maximum slope of the terrain facet is assumed not to exceed 60?, so that an affin 
ratio of down to 1/2 should be provided. Even large scale oblique photographs of forest or glacier 
clad mountain sides could be restituted easily. 
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The orientation procedure could be straightforward, due to the independent parameters: 
1) Bring one diagonal of a quadrangle into coincidence with the conformal zoom. 
2) Place the Perspector in the direction of the mirror reversed parallax vectors, with respect to 
the already coinciding diagonal. 
3) Apply Perspector until the parallax vectors are equal and opposite. 
4) Place the affinity direction as the opposed vectors require, and apply the affin zoom. 
5) Reiterate the procedure to bring the four points of the facet into coincidence. 
Application of a Fácet Plotter could include the compilation, annotation, generalisation 
and in particular the revision of maps. 
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