A comprehensive series of calibrations of a Galileo-
Santoni Special "A" stereometric camera pair was carried
out in preparation for the structural deformation
measurement of a model box girder bridge. The
calibrations are described here. A qoniometer was built
for the infinite focus calibration which in turn was
required as a basis for comparison of the close focus
calibrations. A new method of calibrating the cameras at
less than 4m object distance was then devised, which
proved capable of very high precision. It forms the only
truly original part of this work.
Results of all the calibrations were then examined
and an unexpected change in principal distance was found
at the close focus. The change is shown to be dependent
on the positions of the entrance and exit pupils. The
opportunity is taken to explain an effect known as the
variation of principal distance with object distance, and
to show that this variation is, in fact, non-existent.
A simulation of the structural project was created in
the laboratory and photographed. The photogranmetric
results were obtained first using the maker's value of the
principal distance, then using the principal distance
derived from the infinite focus calibration and finally
from the values obtained in the actual close focus
calibration. The three results demonstrate the increase
in accuracy obtained by calibration, and also the
importance of the lens effect described above.
Details are given of the photogrammetric process used
on the box girder bridge. Finally, a critical appraisal
is made of the use of photogrammetry in a project such as
this