8.3.5. 
8. 3. 6. 
41 
The lateral points are chosen at a distance of the adjacent base of 8/9 of the half- 
size of the photographs. For instance for plates 18 X 18 cm, the distance between 
the nadir point and the lateral points shall be abt. 80 mm. For these points a 
dispersion circle of 10 mm has been allowed. 
The residual parallaxes are measured at by and registered in the form. Their 
determination is carried out in two cycles by observing them twice in the same 
order during two successive series of observations, executed independently, either 
monocularly or with the use of the Dove prism. 
The approximate absolute orientation, giving the transversal inclination of the 
first couple, is obtained on three known control points. 
The definite absolute orientation is determined by computation. 
The reading of the coordinates X, Y, Z of the control points must be done in two 
cycles. 
It is not permitted to make alteration at the relative orientation of the couple 
during the observations. The values of x, y, «, bx and by are registered. 
Two not signalized points situated near the nadir must be used for the transfer 
of the scale. Readings are carried out twice. In order to ensure a good identifi- 
cation of the observed details, the Centres must make a sketch of each point used 
for the transfer of scale. This sketch is made in two copies. One of these is 
attached to the weekly report, sent with the observation results to the Bureau 
Exécutif or the Presidency of the Commission. 
As no pricking has been carried out for the work of B, it was necessary to take 
measures in order to make sure of the correct identification of the special points 
used for the triangulation. 
For the transfer of the X and Y, while observing the connection points of couple 
n with couple n + 1, it is not permitted to modify the indications of the drums of 
the X and Y. 
The relative orientation of the new couple must be carried out by means of the 
parametres x, y, «, by, bz of the new perspective bundle. 
The comparison of the two successive models is done by using two auxiliary 
points, situated above and under the nadir respectively; these points are chosen 
at a distance of abt. 8/9 of the half-size of the photograph from the flight axis. 
The observation of a large number of control points is limited to the special test 
pairs (couples témoin). One of the couples acts as such in each strip or block and 
is generally chosen at the beginning of the triangulation. 
The number of points to be observed in these models is at least 20-25. 
In the other couples of the strip the number of points to be observed has been 
limited, the observations have been reduced to details chosen in accordance with 
the following scheme: 
X X 
X 
x x 
N, 000 N; 
X X 
X 
X X 
If the couple being observed shows a great difference in level, it is advisable to 
read also the heights of at least two well-identified points, of which one is 
situated on the highest place and the other in the lowest part of the model. 
The triangulation must be executed in one sense, starting with the first model in 
which known points are available and following the triangulation to the end of 
the strip.