The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008
3.2.2 Case 2: Real-Time Kinematic Positioning Highway
Mapping
Various RTK survey tests were executed at different distances
from the permanent stations aiming at testing the substructure
and the accuracy quality of the network. The equipment used
was the Leica Geosystems SR520 and GRX1230 receivers. The
initialization test (KIS) was performed using the GRX1230
geodetic GPS receiver in the broader area of the Paralimni town.
The campaign was scheduled in order to have the maximum
GPS visibility. The recording interval for the kinematic chain
was set equal to 2 sec. The measured points were processed
from the two permanent stations of Lamaca and CavoGreko
(southeastern of Cyprus) in order to test the method
effectiveness on various baseline distances. Specifically, the
test distances varied from about 1 to 21 Km.
For every occupied point, we calculated the distance between
the point obtained from DGPS and the one from kinematic post
processing (KIS-PP) (Pala et.al., 2003, Xinhua, WU. et.al.,
2004). In addition, some points of the kinematic also were
measured with RTK in order to simultaneously evaluate the
accuracy of this method against the other techniques. It is
critical to report that several problems came up, mainly due to
obstacles to the radio-modem signal communication. Therefore,
a GPRS connection is preferable (Gao Y., 2002). Also a post
processed single point position (SPP) based on C/A code data
was estimated and evaluated accordingly. A part of the
kinematic chain trajectory starting from the broader area of the
Paralimni with direction to Lamaca is shown on the following
Figure 2.
Figure 2. The GPS Kinematic trajectory
The comparison between obtained positions from phase (fixed)
solutions, using different permanent station data, shows an
agreement at the order of few cm, value which meets the
manufacture’s accuracy specification.
Also, the results confirmed the expected sub-meter precision for
the code differential mode. Such accuracy data are quite useful
for fleet management. In addition, it is proved that DGPS, due
to the high rate of collecting the necessary information, is
probably the best mobile method for map generation (or update)
for scales 1:5000 and smaller. There is no need for initialization,
cycle slip fixing and ambiguity resolution and of course the
installation cost is highly reduced.
solution, for selected points of the kinematic trajectory. As it is
known the height dimension is the mainly affected one so this
quantity was selected to represent the worse case. It is clearly
shown that the differences are lower than 5 cm except for a few
points where the re-initialization was necessary after loss of
signal lock (lower than 4 satellites tracking) (Hofmann-
Wellenhof et.al., 1997).
Height differences between Kinematic - RTK
Figure 3. Height differences between Kinematic and RTK
solutions
In addition to the above test, another survey was concurrently
contacted using only low-cost handheld GPS receivers (at cost
of 300 €), aiming at accuracies at the order of 1 m. The
achieved DGPS results confirmed that accuracies of better than
1 m are achievable under regular survey conditions (Fig. 4).
DGPS Positioning Error
(4.0—5.0) m
(5.0—6.0) m
(3.0—4.0) m 0.2%
0.2%
1%
(2.5-3.0)
6.0 m kqi novio
{2.0—2.5) \ /
3%
(1.5—2.0) m 5%
(0.0—0.5) m
4!%
5%
(1.0-1.5) m S'
16% L ^|H
(0.5—1.0) m
27%
Figure 4. Accuracies of the DGPS solution. In 68% of the cases
the accuracy is better that 1 m.
3.2.3 Case 3: Parcel identification and measurement with
low-cost GPS receivers
This application aims at the evaluation of the performance of
the PSI network in the determination and improvement of the
position of parcel boundaries for the update of the national
vineyard cadastral. With the use of data from low cost portable
GPS receivers as also from the referenced stations of the
Cyprus PSI network, the technique of relative kinematic
positional determination is applied using C/A code data. The
parcels chosen f are shown in Figure 5. The closest permanent
PCI network station is used as a referenced receiver.
The following diagram (Figure 3.) shows the height differences
between the post-processed kinematic solution and the RTK
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