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.