26
A Trimble 4000SE (RTCM input) was placed some meters
away from the former receiver to be linked to the different
DGPS corrections radio receivers. A previous static baseline
was recorded.
Unfortunately, not having the possibility of using more than
one DGPS receiver, we did not got simultaneous sessions
testing the three RTCM correction sources, so that the
conditions were not exactly the same in the three cases.
5158085 —
We took further measurements a week later, on Nov 30th
1999, to compare more results, positioning our Trimble
4000SE receiver on the main reference point.
Fig. 3 shows planimetrie positioning (UTM - ED50) for
RTCM received corrections and reference points.
5158080 —
5158075
¿5 5158070
o
LU
5158065
5158060
DARC
D ..„ 1Ë
r p
LW PRAGUE
t
* DARC (2)
!l ALE (2)
LW PRAGUE (2)
C ALF
416530 416535 416540 416545
ED50 UTM Easting (m)
416550
416555
Fig. 3: Planimetric positioning for RTCM received corrections and reference points; (2) indicates Nov 30th 1999 session.
Frankfurt am Main Podëbrady (Prague)
SAFfC
„DARC(2)
\ ALF<2)
\ O
/LV PRAGUE<2>\
/O
O !
LV/PRAGUE
ALF
Fig. 4: Reference point, mean values and signals’ propagation
direction.
Tables 5 and 6 show the statistic parameters relative to the
measures obtained in different days using Pfinder software,
while Table 7 reports the differences between the mean value
of each distribution and the relative reference point.
In Fig. 4, mean values for each distribution are translated
referring all to one reference point.
As expected (being the source of corrections a few kilometres
away only), DARC diffused RTCM corrections gave the
higher accuracy, even if there were some «bad» points due to
a very high PDOP value (8.6) in Nov 24th measures, or a
probable multipath effect (due to the operators’ presence) at
the beginning of the record of Nov 30th. Anyway good
results and a great repeatability are shown by distributions
obtained by using LW diffused corrections from Podebrady.
This confirms the idea of adopting existing and unused LW
transmitters to cover most of Central Europe by RTCM
corrections dissemination, thus having a continuous and
homogeneous DGPS system, good enough if no very high
accuracy is required.
