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International cooperation and technology transfer
Fras, Mojca Kosmatin

particularly difficult for the reception of the GPS signal
(Fig. 11).
Fig. 11. Measurement of a point with the
GPS+GLONASS RTK technique.
The tunnel is about 2 km long and its course is rather
tortuous, both in planimetry and in altimetry. In fact, we
measured differences in height between successive
vertices only a few hundred meters apart of up to 18
meters. A preliminary marking out performed to obtain
information for the realisation of the working plan was
followed by a rigorous measurement of the vertices of the
polygon. A planimetric precision of 2 cm and an
altimetric precision of 3 cm was required for this
measurement \ The survey was performed with a mixed
technique, GPS+GLONASS and traditional. The satellite
technique was used in the static and fast static mode. The
planimetric orientation of the GPS+GLONASS survey
was carried out with some trigonometric vertices of the
first order network and a vertex of the IGM95 GPS first
network. For calculation of the orthometric heights of the
tunnel’s course, we performed an altimetric link, by
trigonometric levelling, of some datum points in the area.
During construction of the tunnel, after the surveys had
been performed, we proceeded to control the excavation
operations. This was carried out by sampling some
These precisions are required whenever the excavation operations in a
tunnel are performed with an in-line tunnelling machine.
vertices of the polygon, selected on the basis of their
position along the course (start of tunnel, end of tunnel
and where the conduit intersected various constructions
and existing works: a railway link, a cave, a hospital,
etc.). The control was performed with the traditional
topographical technique and the GPS+GLONASS RTK
technique; the established precisions were close to those
indicated in the measurement of the vertices. The RTK
survey was carried out with the same instrumentation
described in section 1. The radio link connection was
realised with a Satel AS2X with selectable frequency and
directional antenna; this apparatus permits larger ranges
than the conventional ones and thus is particularly
suitable in the presence of vegetation. The threshold
filters for the fixes were selected at 4 cm for planimetry
and 3 cm for altimetry. The acquisition interval was set at
1" and the cut off at 5°. The measurement session lasted
one hour. For the co-ordinate transformations, we used
the parameters calculated during the static
GPS+GLONASS survey. Despite the difficult operating
conditions, there were always 5 satellites visible, with a
PDOP never greater than 3. The cycle losses were
frequent, but the apparatus was always re-initialised in the
minimum possible time. The traditional survey was
performed with a NIKON DTM850 integrated station.
Table 2 summarises the mean values (and range) of the
absolute differences between the co-ordinates of the
sample points measured with the GPS+GLONASS RTK
instrumentation and the co-ordinates of the same points
measured with the traditional instrumentation.
Differences in the
Mean value
Table 2. Differences in the co-ordinates measured with
the RTK technique and with the integrated theodolite.
The results of this test revealed the following aspects:
• the acquisition capacity of the GPS+GLONASS RTK
system even in the presence of vegetation and
obstacles to signal reception;
• minimum times of re-initialisation;
• the possibility of operating with a fix filter that is very
low in relation to the operating conditions;
• precisions of positioning comparable to those
obtained with traditional topographical
The availability on the market of GPS+GLONASS
receivers on the L1-L2 frequency has led to appreciable
advantages in operational geodesy. In this paper, we have