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Title
International cooperation and technology transfer
Author
Fras, Mojca Kosmatin

41
Hood Section
b ~ 13 m
Fig. 9. Transverse section of the road embankment.
The GPS+GLONASS RTK survey consisted of:
• repositioning the planned sections on the ground,
during the various repetitions;
• measuring their variations.
The measurements were taken twice a week for six
months. The bi-weekly survey of a road embankment was
performed in this way. The operator positioned the
Master receiver on a vertex of known co-ordinates and
initialised the Rover receiver, with a standing time of no
more than one minute. At that point, he performed the
operation of plane calibration: within the GPS reference
system, he measured the co-ordinates of at least five
points on the ground which had co-ordinates known also
in the local system. When the double set of co-ordinates
was entered into the CDU-2, the parameters of the plane
calibration for passage from the GPS+GLONASS co
ordinates to the local ones were calculated (Fig. 10). The
maximum differences in the calibration were never
greater than 5 cm.
Fig. 10. Display of the Field Face Program in the CDU-2.
When the parameters of the calibration and the planned
co-ordinates of the sections were stored in the data
logger, the operator proceeded with the measurement of
the points in transverse directions. During the
measurement operations, the acquisition interval of the
single receivers was set at 1 sec and the minimum cut off
of the satellites at 5°. The survey of a single road
embankment, including the operations of repositioning,
lasted from 1.5 to 2 hours. In this time period, 15 to 20
sections were measured, i.e. 300 to 500 points.
The number of visible satellites was never less than 12-
13: on average 8 GPS and 5 GLONASS. The PDOP was
never greater than 2. In this way, it was sufficient to stay
with the Rover receiver on the survey points for no more
than two epochs of measurements (Fig. 7 and 8). The
same survey was performed with equipment similar to the
previous one but with receivers for only GPS
measurements in double frequency L1-L2 (GPS RTK).
The sampling interval was the same (1") and the cut off
was increased from 5° to 10°. With this equipment, the
interruptions of the signal were more frequent, especially
in correspondence to the scarps of the road embankments
which reach considerable heights and inclinations (Fig.
9). The number of dynamic re-initialisations was
increased and with them also the respective times of static
(of initialisation and of a single fix) and dynamic
stationing. Moreover, to permit the Rover device to
receive many satellites and therefore to record the
position, we were often forced to leave the area of
measurement, with a considerable increase of the
difficulty of surveying. From the operational point of
view, the experiment showed:
• the considerable capacity for acquisition of the
GPS+GLONASS RTK system, especially in
conditions particularly unfavourable for reception of
the signal, e.g. during the survey of scarps or the
calibration on vertices situated near electric power
lines;
• the good reception of the radio link signal from the
Master to Rover, which never suffered interruptions
that might compromise the execution of
repositionings and fixes;
• the reduced times of static initialisation and dynamic
re-initialisation;
• the good planimetric and altimetric precision, always
within the tolerances established by the client;
• the limitations of the GPS RTK system, both in the
phase of initialisation and the phase of acquisition.
Table 1 shows a comparison of the measuring times and
number of operators employed in the two satellite
techniques, as well as in the survey with an integrated
theodolite, for an equal number of points measured (300-
500). It can be seen that productivity was increased by
about 30% with respect to the traditional instrumentation,
while the presence of operators was reduced to the
minimum (only 1 GPS or GPS+GLONASS operator
versus 1 theodolite operator + 2 rod holders).
Measuring techniques
Measurement time
(minutes)
Operators
Integrated theodolite
240-300
3
GPS RTK
120-180
1
GPS+GLONASS RTK
90-120
1
Table 1. Comparison of the measurement times and the
number of operators for the different survey methods.
2.2 Localising reference points in woodland for a
water supply tunnel
The second application involves the checking of the co
ordinates of some vertices of an axis network for the
organisation of the course of a water supply tunnel. These
vertices are situated in an inaccessible wooded area,