provide precise forced centering of the instrument. Next, the
team determined which bogies to monitor. Over time, some
of the bogies had been treated with grease to reduce friction.
In order to provide a complete assessment, the team decided
to monitor six of the treated bogies and the same number of
untreated bogies. They installed mini prisms on each bogie,
using clamps to prevent damage to the historic structure.
The technicians then used the Trimble S8 to establish precise
relationship between the two mounting plates. The instru-
ment measured across the cupola to a prism installed on
the opposite mounting plate, and to an orientation point
visible from both stations. They repeated the process from
the second mounting plate. Because of the difficult access,
the technicians used the Bluetooth connection and Trimble CU
controller to operate the instrument remotely from a safe
location about 15 m (50 ft) away. The Trimble S8 AutoLock™
functionality could automatically point the instrument
to the center of the prism targets to produce fast, precise
With the setup operations complete, the technicians
proceeded to survey all the points on the bogies from
both stations. Using Trimble Access software, the process
conducted six measurement cycles at intervals of four hours.
Each point was measured 10 times per cycle.
In order to track the thermal expansion of the arches, the
teams used a thermal camera and ambient thermometer
to measure temperatures in the cupola three times per day.
Among the thermograms obtained, six referred to moni-
tored bogies and one to the ceiling of the cupola. Ambient
temperature was during the periods when the total station
measurements took place.
The Structural Model
During the operation’s planning phases, DICAM experts had
predicted the bogies would move along only the X and Y-
axes, with practically no motion in the vertical component.
The monitoring measurements confirmed their prediction.
The movements occurred in a range between -0.4 mm and
0.4 mm (-0.02 to 0.02 in). By combining the thermographic
and total station measurements, the researchers could de-
velop a structural model of the cupola. The model indicates
that a temperature variation of 1°C (2°F) corresponded to a
movement of 0.1 mm (0.004 in) in the bogies. While the mo-
tion is almost imperceptible, the cupola structure is able to
accommodate the thermal expansion. After more than 100
years, the bogies are still performing their task perfectly.
Thanks to the expertise of the University of Palermo team and
the advanced survey technology, the spirit of the Massimo’s nun
can continue to wander peacefully through the theatre’s halls.