Särtryck ur Svensk Lantmäteritidskrift, nr 3, 1964. 
495 
A Bridging Method with Correction for the 
Influence of Earth Curvature and Conver 
gence in the Individual Model the Effect 
of Correction for Earth Curvature 
By Knut Thulin 
Some critical views on the ordinarily used theories for bridging 
Theories for bridging and adjustment methods for bridging have 
been developed a long time ago and are still of current interest. 
The practical results of bridging, however, have not always been as 
good as the theories have promised and in a report on the results of 
the triangulations and adjustments carried out by Commission A of 
OEEPE [1] is for instance stated that the results in many cases dif 
fered significantly, sometimes they were even contradictory. 
One of the most important reasons for the difficulties to receive a 
good result from bridging has been that the influence of the curvature 
of the earth has been neglected or not correctly treated. 
In photogrammetric literature there are many examples. The follow 
ing can be mentioned. 
The classical bridging method 
In textbooks we can read that the absolute orientation of a new 
model will be automatically performed with the relative orientation. 
Only the new photograph may be altered and this conjunction of 
successive photographs in a strip is a postulate for bridging. 
Professor R. Finsterwalder says in ¡2] that this method gave rapidly 
increasing systematic and unavoidable errors, primarily elevation errors 
of second degree. He says nothing about the influence of the curvature 
of the earth among the reasons to the errors. 
The reasons may be found in the conception of the straight aerial 
traverse. 
The straight aerial traverse 
In [3] we find: 
»Dabei denken wir uns das unverfälschte Gesamtmodell mit ge 
streckten einander parallellen Zügen der Projektionszentren P und 
der Modellnadire N, einander gleichen Basislängen b und Projektions 
abständen h der einzehren Teilmodelle (Abb. 371)».