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is placed over the horizontal reference plane table. To precisely define the 
position of the plane surface with respect to the projected model, a grid pattern 
of small light spots is also projected onto this same surface, thus giving the 
illusion of a transparent plane passing through the projected model. Changes 
in elevation of this plane are accomplished by the vertical movement of the 
projectors, and when these are set to the desired elevation, the operator traces 
the contours or other information onto the plotting surface. 
Experience indicates that this method is somewhat faster than conventional 
methods for medium and small scale mapping and the topographical detail 
plotted tends to give a better graphic portrayal of the terrain being mapped. 
This is partially explained by the fact that the operator has a better opportunity 
to employ his knowledge of »topographic expression». It is also apparent that 
this system holds the interest of the operator more than those which restrict 
the viewing area. 
Besides its application to mapping, the advantages of this system for geo 
logical, forestry and agricultural and other studies such as pipeline, railroad 
and highway location are obvious. 
Table à dessin et à traçage combinés pour emploi conjoint avec les 
stéréoprojecteurs du type Multiplex 
L’emploi d’une table spéciale pour combiner le dessin, et le traçage permet de tirer pleinement 
parti des caractéristiques spéciales des stéréoprojecteurs du type Multiplex en fournissant au techni 
cien une vue d’ensemble du modèle stéréoscopique tout entier. Le technicien peut ainsi utiliser 
pleinement l’acuité de sa vue normale et ne compte pas entièrement sur l’acuité de la vision stéréo 
scopique. De plus, vu que le traçage se fait directement sur l’image projetée, chaque ligne que l’on 
dessine fait l’objet d’un contrôle automatique. 
La méthode consiste à diriger les images fournies par les projecteurs Multiplex sur la table 
horizontale qui forme le plan de référence et sur laquelle on a fixé du papier à dessin blanc ou 
d’autres produits se prêtant au traçage. On projette également sur cette surface une série de points 
lumineux qui créent l’illusion d’un plan transparent au niveau du dessin. Le mouvement vertical 
des projecteurs assure les changements d’élévation. 
Pour la cartographie à petite échelle ou à échelle moyenne, la méthode semble plus rapide que 
certaines autres méthodes utilisant la projection car le traçage se fait à main levée. De plus, les 
détails que l’on trace assurent une meilleure représentation graphique du terrain. On a également 
constaté que la méthode porte la technicien à s’intéresser davantage à son travail. 
L’emploi de cette méthode de traçage peut être étendu à d’autres domaines, tels que ceux de la 
géologie, de la sylviculture et de la voirie (tracé des routes). 
»Theoretical principles of construction on which the recent O.M.I.-Nistri 
plotters are based», par M. U. Nistri, Italie. Resume: 
The author refers to articles of his which have appeared in various Italian and 
foreign magazines and in which he has illustrated the evolution of his ideas in the 
course of practice and from daily experience acquired during more than thirty 
years of photogrammetric activity. 
After having made mention to technical and practical criteria that have guided 
him in the realization of his new photogrammetrical instruments presented at this 
Congress, he recalls that his antique predilection for the double direct optical 
principle has not hindered him from turning his attention and his studies to 
universal plotters with stereoscopic binocular vision. In this respect he cites his 
Photostereograph mod. Alfa presented at the Congress of Photogrammetry held 
in Paris in 1934. This instrument and his creation of the Multiplexes demon 
strate how, since then, he has been guided by the sound conception of adopting, 
for each instrument, the most suitable principle for the different technical and 
economical needs in the practical employ of photogrammetry. 
Thereafter he refers to the principle on which the Photostereograph mod. Beta 
is based, and to the characteristics and advantages of its realization which, 
to the well known and appreciated virtues of the Porro-Koppe principle, unites 
U. Nistri: Theoretical 
principles of construction 
on which the recent 
O.M.I.-Nistri 
plotters are based.