(354) 
As the precision of the plotting is above all a function of the negative 
scale, a little precision is gained if the stereoscopic image is formed at a scale 
clearly larger than the scale of the negatives; this is not to say that in every case 
if the drawing is at the scale of the stereoscopic image, the map at this scale has 
corresponding precision. 
Universal plotting machines are generally limited by their dimensions, 
particularly by the amplitude of their Z movements, 
On the contrary, apparatus such as the Multiplex or the Kelsh Plotter are 
confined to an important minimum magnification about 2.4 for the Multiplex 
in reference to the air negatives, (about ten times to the diapositive) and a mag- 
nification of 5 times for the Kelsh Plotter. 
In France for example with the Poivilliers Type B, one can, for negatives 
at 1 :25,000, form the image at'1+10,000 for a focal distance of 125 mm. No 
more for a focal distance of 150 mm. 
The scale of the negatives has been fixed when the scale of the map is estab- 
lished; the scale of the stereoscopic image is chosen as large as possible. But for 
choosing the plotting scale compared to the scale of the map the solutions 
adopted differ; for the Multiplex and the Kelsh Plotter, the plotting scale is 
necessarily the scale of the stereoscopic image and the map is always on a much 
smaller scale, 2 or 5 times smaller. 
Universal plotters sometimes draw at the scale of the stereoscopic image, 
the plot being reduced afterward to the scale of the map; sometimes the plot is 
made approximately the same scale as the map. 
The first plan of operation is followed in Austria for example. Image 1: 
: 12,500 plot 1 : 12,500, map 1 : 25,000. In France for the 1: 100,000 of the ter- 
ritories, image 1 : 25,000 to 1 : 50,000, plot 1 : 50,000; for the map of N. Africa 
image and plot 1 : 40,000, map 1:50,000; for the map of France at 1 : 20,000 
with negatives 1:25,000 taken with 150 mm focal length images, trace and 
map at 1:20,000. In the Netherlands the relation of the scales is generally 1. 
In Canada plotting is at 1 : 10,000 or 1 : 15,000 for 1 : 50,000 scale maps. In the 
USA with universal plotters the scale of the plot is about 20% greater than the 
map. In Sweden, with Wild A6 the ratio is 1, with the Wild A5 or the Zeiss 
Stereoplanigraph, 1/1.5 or !/. The Italian Geographic Institute uses 1 : 12,500 
image 1 : 20,000 plot and 1 : 25,000 map. The EIRA and Cadastral Service uses 
plots twice the map scale. The Belgian IGM has adopted a ratio of °/s between 
plot and map scales. 
Generally, a maximum stereoscopic image scale is chosen with the scale of 
the plot equal or larger than the map (to improve the plot by reduction). It 
is above all the scale of the negatives in relation to the map that is important, 
not the scale of the image or even less the scale of the plot. 
Methods of Relative Orientation. 
One can distinguish three main kinds of methods for forming the stereo- 
scopie model: 
1. Those which are based on measurement of parallaxes and calculation 
of the elements of orientation or of their residal errors; methods rather com- 
plicated and more convenient for air triangulation rather than plotting. 
2. Those which are based on graphic methods permitting rapid, suffi- 
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