30 O.E.E.P.E., Commission A 
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Results of Bridging and Adjustment Works of the Commission A 
of the O.E.E.P.E. from 1956 to 1959 
by LUIGI SOLAINI and CARLO TROMBETTI. 
1. During the period from 1956 to 1959 eleven European Centers have carried out for 
the O.E.E.P.E. Commission A, 111 bridgings using aerial strips 90 to 100 km in length, 
including 40 to 50 photograms each. These strips were referred to at the preceding 
Stockholm Congress. 
As a rule, the bridging of a strip has been repeated with the plotting instrument; the 
first time starting from an internal base, and the second time from an external one. 
The methods of bridging which have been used in preference were the one with 
bz = 0, the statoscopic and the solar ones. 
The Commission prepared a report where the qualitative results obtained are given; 
at present it is in print. Successively particular studies on specific problems will be com- 
mitted to some Centers. 
2. The study of bridging methods has been carried out on co-ordinates resulting from 
the bridging itself. The instrumental co-ordinates were previously transferred to the first 
model system and submitted only to a linear distribution of closing errors in X, Y, Z, for 
the purpose of reducing errors along the strip to a quantity which could be better re- 
presented graphically. For the triangulations with bz = 0 and statoscopic bz the Z were 
corrected for the differences between the two values of y of the photogram common to 
the two successive pairs. 
The strips could dispose almost for each stereoscopic pair of points on the ground 
determined using classical methods of triangulation and levelling, so it has been possible 
to calculate the real errors of the points of the bridged pairs, near the axis of each strip, 
so as to allow an accurate study along each axis. 
258 curves of error have been constructed (86 for each coordinate X, Y, and Z). Of 
these: 123 refer to the method bz — 0, 72 to the statoscopic and 54 to the solar methods. 
3. The study on the above mentioned “curves of error” has been carried out separate- 
ly for the three methods of bridging and finally comparisons of the whole matter were 
carried out too. 
First of all the examination was concerned with the resemblance of the two curves 
of error concerning two bridgings starting respectively with internal and external bases 
assuming the most similar working conditions. Such a repetition of the passage outlines 
the influence of the instrument in the propagation of systematic errors. 
Afterwards a judgement was expressed on the regularity of the same curves con- 
sidering chiefly their longitudinal symmetry: this phenomenon has its more evident 
repercussion in the simplicity of adjustment laws. 
Finally it has been given the statistical distribution of the maximum entity of the 
errors of each bridging, dividing it into three intervals: errors less than 20 meters, those 
between 20 and 80 meters, and those greater than 80 meters. In effect a maximum error 
of 20 meters in planimetry can be overlooked in plotting at medium scale, without carry- 
ing out any adjustment; while errors greater than 80 meters cannot be easily tolerated 
even by means of adjustment. 
3.1. The strips bridged by the method bz — 0 which start from an internal base have 
often caused (6096) curves of error similar to those starting from an external base. The 
course of the curves of error has frequently been (45%) very regular. 
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