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154 RELATIVE ORIENTATION IN MOUNTAINOUS TERRAIN, DISCUSSION 
mately flat terrain, and the formulae for this 
type of terrain which was present in the Monti 
di Revôira experiment. 
As you can see from the table there are 
three elements which are unchanged: the dby., 
the dz» and dg». The corrections came out for 
rough as well as for flat terrain, depending 
upon the actual shape of the terrain in that 
case. 
Then we have the other two elements: the 
db. and do». There are differences, but for the 
standard error of unit weight soy there were no 
differences which could be noted. Consequent- 
ly, in that case we used the formulae for flat 
terrain for the computation of certain of the 
elements of orientation and also for the deter- 
mination of the standard error of unit weight 
which defines the accuracy of the relative 
orientation after an adjustment. 
Further we had the opportunity to test the 
formula for error-propagation from the relative 
orientation through the absolute orientation to 
the final results of the plotting. As you can see 
from Table 1 in the Additional Remarks to 
the General Report of the sub-Commission 
IV:4, there is very good agreement between 
the theoretical and the practical results, al- 
though in that case we used nothing but the 
mean square value of the measured y-paral- 
laxes in nine points as an expression for the 
sy here. This means an approximation, yet the 
results agreed so well, but I certainly hesitated 
to publish them from the beginning. 
With these words I just wanted to say that 
the actual shape of the terrain is very impor- 
tant, of course. Monti di Revôira represents 
just one of the infinite number of possible 
shapes of the ground. 
Mr A. J. VAN DER WEELE: I should like to 
thank Mr Hallert for his contribution, particu- 
larly with regard to the formulae for the com- 
parison of flat and mountainous terrain. 
Is there anyone from the floor who wishes 
to make additional remarks or who has a 
question? 
As this does not seem to be the case, I 
declare this session closed as far as this par- 
ticular subject is concerned.