n of the negative 
formed at a scale 
that in every case 
p at this scale has 
their dimensions, 
Kelsh Plotter are 
tor the Multiplex 
itive) and a mag- 
an, for negatives 
of 125 mm. No 
the map is estab- 
possible. But for 
ap the solutions 
plotting scale is 
ways on a much 
reoscopic image, 
times the plot is 
imple. Image 1: 
2,000 of the ter- 
iap of N. Africa 
ice at 1.: 20,000 
nages, trace and 
s 1s generally 1. 
ale maps. In the 
greater than the 
A5 or the Zeiss 
uses 1.:12,500 
ral Service uses 
) of ?/s between 
ith the scale of 
y reduction). It 
it 1s Important, 
ing the stereo- 
nd calculation 
Is rather com- 
lotting. 
g rapid, suffi- 
(355) 
ciently accurate solutions of the problems obtained by calculation in the first 
group. 
3. Those which are based on successive approximations. 
The last two simple classes can be done by operators who have very little 
knowledge of mathematics. 
Most of the national reports considered the third class sufficient for plot- 
ting; the optical-mechanical method of Von Gruber or its derivitives are usual- 
ly employed (elimination of the parallax at the nadirs, and over-correction at 
one of the nadirs by adjusting the cross-tillt W and swing). 
Let us recall that this method is theoretically applicable only to negatives 
nearly vertical and to level terrain. 
Sweden, Switzerland, Austria, USA, Italy (IGM and E.LR.A.) and the 
Public Works Ministry of Belgium report current use of the Von Gruber Me- 
thod. 
Sweden reports that in special cases the calculation method of Hallert is 
also used, Switzerland also indicated the empirical method of Zeller-Branden- 
burger. 
Austria indicated that for scientific purposes the graphic method of Krames 
is employed though still in the trial stage. In Italy, for oblique negatives the 
graphic method of Santoni is also used. This method uses the measured paral- 
laxes of six selected points, the height of the apparatus and the inequality of 
these parallaxes symetrical to the base. 
The IGM of Brussels and the IGN of Paris use a novel graphic method 
invented by M. Poivilliers since the last Congress for orientation of the stere- 
oscopic model. (See summaries of this report). This method is in entirely 
rcutine application at the two organizations, including its use for aerial trian- 
gulation. Its great value is to require only three points of the image in a 
plane perpendicular to the base at any abscissa. This condition is particularly 
important because it permits the choice of a plane so as to avoid regions near 
indeterminate conditions for a model of high relief, or in the case of partial 
models (models with coast lines or large areas of water) to chose the most 
favorable section for the working of the graph. Finally the graph with which 
the method is applied is very simple, consisting of the intersection of two 
straight lines. 
In summary, the numerous analytical studies made on the formation of 
the stereoscopic model and the errors of relative orientation are only very little 
embodied in practical methods conveniently used by operators who are little 
accustomed to calculations, and permitting simple solutions of the problem. 
If theoretically these procedures are most interesting for aerial triangula- 
tion, they are not less interesting for plotting unusual models or those covering 
rough terrain. 
Let us note the particular method applied in Finland: first, the nearly 
absolute orientation of each negative from images of the horizon; next, refine- 
ment of the relative orientation, then refinement of the absolute orientation 
on the ground control. 
Methods of absolute orientation. 
Some of the National reports said only that absolute orientation is ob- 
tained by ground control or air triangulation.