233 
Mr. Wassef recommends the use of statistical methods to establish the distinction between 
different types of errors. He feels that the comparison only of the final results does not permit 
a good confrontation of the methods. 
Mr. Verlaine wonders why all tests are executed without using auxiliary equipment and why all 
compensations have been made bloc-wise. He desires that future work fill up this gap. 
Le président indique qu’il pourra être tenu compte de ce voeu dans l’organi 
sation de la suite des travaux. 
Il clôt les débats à 11 heures et cède la parole à M. Bachmann (Suisse) qui 
présidera la séance consacrée à l’essai no 2. 
The president indicates that during the organisation of future work, this wish can be taken 
into account. 
He closes the discussion and leaves the chair to Mr. Bachmann to preside the session devoted 
to test nr. 2. 
(Voir la séance de la commission II, page 171.) 
La séance du 23 juillet 1956, à 9 heures (c) 
Le président ouvre la séance à 9 heures 05 et donne la parole à M. L. Ekehmd 
(Suède) pour sa communication intitulée: »Photogrammetric Triangulations 
controlled by local Geodimeter Basis or Polygons». Un résumé de la com 
munication est ainsi conçu: 
Introduction 
In the north of Sweden there are waste areas still lacking geodetic control 
net. As there is a great demand of photogrammetric large scale maps in this 
part of the country — especially for hydroelectric works — the control survey 
is an important current problem. Generally a control net is produced through 
stereo triangulations in first order stereo machines. The scale is often determined 
by means of local bases. Up to now the bases are measured on the ice of large 
lakes or rivers. The development of the Geodimeter — the electro-optic distance 
measuring instrument by Dr Bergstrand — has given the geodet and the photo- 
grammetrist new possibilities to control maps in a simple way. The instrument 
makes it possible to determine bases 5—40 km in length with an accuracy of 
1: 500 000. 
The stereotriangidation method 
A special aero triangulation method »model triangulation» has been developed 
which is especially useful in these cases when the planimetric control survey is 
performed by local bases. The principle of the method is published in (1) and (2). 
The stereo models are separately orientated in the instrument and then nu 
merically transformed to one system. The connection points are drawn on the 
negative as fine crosses. 
Influence of systematic instrument errors on the shape of the triangulation 
strip is eliminated by turning every other model 200 s when putting the pictures 
into the plotting machine. 
The effect of this turning procedure has been investigated by practical tests 
and by grid measurements in A5 and A6. In a ten model strip triangulated in 
A5 the x- and y-errors were reduced to less than 1/5 thanks to this turning. 
Tests have also been performed to transfer the scale and azimuth between the 
models on mechanical way. (3) 
L. Ekelund: Photogram 
metric Triangulations 
controlled by local 
Geodimeter Basis. 
(Publ. HIE 1)