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excluded, i.e. those where comparison was not
possible.
A vectorial diagram was also traced
in which each vector indicates the differences
between the examined and reference phases.
From these results it was noted that the maximum
vertical displacement was 16.6 mm reached during
phase 30 (figure 2).
Another processing was carried out in order to
control the platform's tensional level. For this,
the points were subjected to rigid
rototranslation, i.e. maintaining the reciprocal
distances in order to minimise the deviations.
The result obtained was that of greatly reducing
the size of the deviations passind to a maximum
value of 6 mm. It was thus assumed that the
deformations were mainly due to rigid movements of
the structure and so the tensional state of the
elements were not increased greatly during the
loading operation.
7. CONCLUSIONS
The survey results showed that the structure
undergoes small stresses. So, from a structural
point of view, the jacket had no problem during
the load out.
The photogrammetric survey gave good results in
terms of accuracy and quantity of data.
Stereophotogrammetry was tested in detail in
shipyard surveys and did not create special
problems even although it was used in very bad
environmental conditions with little nightime
light and the shooting had to be carried out in
very limited times.
The survey could not have been carried out using
any other method because the topographic measuring
requires times which would have been unacceptable.
One possible adjustment to allow a better
structural analysis could be to evaluate the
lowering of the boundaries ie. the launching beam
and the boat by geometric levelling.
The main result is undoubleddly that of having
verified the possibility of using
stereophotogrammetry to measure large structures
which may even be in movement.
This method also gives results in a very simple
form which may be processed for other aims such as
structural analysis or CAD representation.
8. ACKNOWLEDGMENTS
The author expresses his gratitude to Agip for its
permission to publish this report. Many thanks
also to colleagues from Industrial Photogrammetry
for the cooperation given during the survey and to
colleagues from the EDPI group for designing the
data processing programs.
Finally, special thanks also go to the Intermare
yard at Arbatax (Italy) for its cooperation during
the survey.
9. BIBLIOGRAPHY
References from BOOKS:
American Society of Photogrammetry, 1989.
Handbook of non-topographic photogrammetry. XI
Edition, pp. 349-356
References from JOURNAL
G. Bozzolato 1988. A new photogrammetric
procedure for offshore engineering surveys. The
photogrammetric record. 13(74): 277-287
References from GREY LITERATURE:
M. Rampolli, E. Bonora, 1990. CAD system use for
photogrammetric measurements of Agip's offshore
structures. In: Int. Arch. Photogramm. Remote
Sensing. Zurich Switzerland, pp. 349-362
M. Rampolli, 1990. Dimensional verification to be
carriede out at open sea on offshore structures by
means of photogrammetry. Int. Arch. The
European Oil and gas Conference.SER.
Palermo-Italy, p.409