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AERIAL TRIANGULATION WITH AUXILIARY DATA, DISCUSSION 103 
introduction of auxiliary data provide a greater 
elasticity than the instrumental one. Experience 
at our Institute led us to the conclusion that it 
is always preferable to introduce auxiliary data 
as an element of absolute orientation of models, 
especially owing to the present scarce precision 
of the data themselves. Furthermore, we wish 
to point out that the introduction of auxiliary 
data is very simple in analytical triangulation, 
since it requires only a slight modification of the 
general computation programme. Also, for solar 
triangulation which usually appears to be rather 
laborious, the preparation of a suitable and 
simple calculation programme allows us to de- 
termine quickly from the solar co-ordinates on 
the photograph the data necessary for the ca- 
mera orientation. 
Let us examine now in more detail the 
statoscopic triangulation and the solar one. In 
regard to statoscopic triangulation, we have 
already had the opportunity to remark that the 
idea considered in Dr Brandenberger’s report, 
of an improvement of the statoscopic data to 
be obtained when considering the A rotations 
of the fixed camera in instrumental triangu- 
lation, is purely illusory. In fact, it gets rid of 
the bz absolute value introduced and takes the 
statoscopic triangulation back to one which is 
similar to the triangulation with bz = 0. 
On the contrary, a method of correction of 
at least a part of the statoscopic accidental er- 
rors — which we successfully experienced re- 
cently with analytical methods — is as follows. 
First of all, the strip is calculated and the 
heights of the camera are recorded. The dif- 
ference will be made between those heights, 
after the linear distribution of the closure er- 
ror, and the ones obtained from the statoscope. 
A diagram of the same differences will be 
drawn. An interpolation curve is built, allowing 
us to calculate — even if it is empirically — 
sufficiently approximate values of accidental 
errors of the statoscope. However, this is not 
a new method since it is also used with radar 
profile methods. 
Finally, each model is turned taking into 
account the corrected bz statoscopic compo- 
nents thus determined. The analytical method 
lends itself particularly to the application of the 
simple proceedings because the accidental er- 
rors of each model are really very small. 
The results which have been obtained until 
now are encouraging, since the mean height 
error of the camera, with a simple statoscopic 
triangulation, in a 100 kilometre strip taken 
from 4,500 metres altitude, equal to + 3.6 
metres, in this way is reduced to + 2.8 metres. 
Experiments are continuing on longer strips 
and also on very rugged terrain. 
As far as solar triangulation is concerned, 
the analytical method allows us to apply the 
solar data more widely than is done instru- 
mentally. In fact, using the plotting machine 
we are practically obliged to compute omega 
from the knowledge of while analytically it 
is possible and may be convenient to derive 
q or o from the free bridging and to calculate 
the other two rotations through the co-ordinates 
of the image of the sun. 
By analysing the problem in theory, the 
conditions have been determined in which we 
may use one or other of the indicated pro- 
ceedings so as to be sure to attain a sufficient 
accuracy. 
Of course, good results from these pro- 
ceedings depend, for the most part, on the pre- 
cision of auxiliary instruments. We have been 
pleased to read about the results obtained by 
Dr Brucklacher with statoscopic triangulation. 
As for the sun, which already supplies good 
proximation, we deem it possible to increase 
precision to the extent of obtaining the direc- 
tion of the rays of the sun with an approxima- 
tion similar to the one of the direction going to 
the point of the ground. 
We have begun at our Institute to experi- 
ment with the different proceedings of the in- 
troduction of solar data and their coupling 
with statoscopic ones, although the photogra- 
phic material at our disposal was not taken in 
the most suitable conditions. In the near future, 
we will carry out a more intense experimental 
research on long strips. 
Prof W. SCHERMERHORN: This is a very im- 
portant subject in aerial triangulation. It has 
already occasioned this morning a discussion 
between myself and Mr De Masson D'Autume. 
A lot of work is being done in this field in dif- 
ferent places. Only part of this has been made 
public. If possible, next Wednesday there will 
be another meeting of Commission III in the 
afternoon. There will be two successive hours. 
At 1.30 we shall have a discussion on the report 
of experimental works organised by Commis- 
sion III and then at 2.30 a discussion on the 
general report of Commission III and the pre- 
paration of resolutions. I hope that it will be 
possible to curtail those discussions to such an 
extent that we may give more space to this 
most important subject; perhaps we can cut 
down a little on those which are less important. 
  
  
  
  
  
  
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