61 
Because the triangulation should be carried out after the so-called free method i.e. 
without any condition, only the elements of orientation of the new camera have been 
employed. For two strips the statoscope has been recorded during the flight; the relative 
data have, however, not been used. 
For the triangulation with the Stereosimplex III used by the Delft Centre, special 
procedures had to be adopted, because this instrument has no means to reverse the base 
and the observation of the photographs. 
With the aid of grid measurements the zeros of the instrument have been carefully 
determined; afterwards the photos were transported, while taking into account the dif- 
ferences of the zeros between the two cameras. 
In all cases the residual parallaxes have been read twice and registered; hardly ever 
do they exceed 0,03 mm; in general they are less than 0,02 mm. The mean square value 
is for all Centers lower than 0,01 mm on the model, i.e. in all cases lower than 5 u in the 
plane of the photographs. 
The azimuth of the first model was established in such a way as to eliminate as mue 
as possible the necessary change of b ; as it was not furnished by the Presidency of the 
Commision, its value is not exactly “equal for the same strip. The absolute orientation 
was effected in an approximated way by two Centres, and by the others until a satis- 
factory precision was obtained. 
As the photographs were not pricked, two or three points near the nadir were chosen 
for the transfer of scale; sometimes, as a check, also the heights were read of two points 
situated on the line perpendicular to the base passing through each nadir, but without 
changing the relative orientation or the base. At the Delft Centre three points were prick- 
ed on each plate for the comparison of two successive couples. The concordances between 
the coordinates of the lateral points determined in two successive couples, were generally 
gocd; the Centre in Ziirich remarks that the differences are smaller for the wide-angle 
photographs. 
After each connection of images the coordinates of two control points were read in 
two successive cycles, according to instructions given by the President of the Commission. 
The number of these points, which were very numerous, has been reduced during the 
work, because the reading of the coordinates took too much 
time, and also badly influenced the precision of the trian- 
be 
d 
X X X gulation. 
The location of the control points should, as much as 
N 0 0 0 N, 
; = possible, be similar to that in the figure. The Centre in 
X Ux x = ; : 
Vienna has observed an average of: more than 16 !) points 
X X per couple, that at Delft: 5-6?) and the Centre in Zürich 
7,6 and the EIRA: 7,5. 
The time needed for each connection varies between two and three hours, depending 
on the dispositions which the Centres have taken for the different operations, i.e. the 
number of points chosen for the transfer of scale, the observed control points, the training 
of the operator; the method of relative orientation, etc.; of this total time half has been 
devoted to the reading of the coordinates of the control points. 
In general no difficulties have been encountered during the work; only three diapo- 
sitives of test III, sent to Delft, showed a considerable reticulation and one photograph 
sent to the EIRA had perhaps a local deformation which rendered the relative orienta- 
tion very difficult. 
Not all control points were properly visible; those situated on the roads showed not 
sufficient contrast with the background, which caused difficulties for the identification 
and the pointing; this concerns only 10—1596 of the number of established points. 
1) Only the original strips (IX and X), flown by Austria, have been triangulated. 
?) Though about 8 points could have been used, the observers, wrongly, discarded the center 
points.