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Proceedings International Workshop on Mobile Mapping Technology
Li, Rongxing

Figure.2 Management Diagram of “MultiGateStation”
There are two methods of high-accuracy GPS-based
positioning: Differential GPS (DGPS) and Real-Time
Kinematic GPS (RTK-GPS). As shown in Figure 3, DGPS
is a GPS-based positioning technique in which a GPS
receiver is set up at a known location and at a meas
urement location, and range errors at the measurement
location are corrected by transmitting range errors meas
ured at the known location (ARn) to the meas-urement
location as correction data. The positioning accuracy of
DGPS is several meters (about 1-2 m in the horizontal
direction and about 3-5 m in the vertical direc-tion), which
are suitable for rough positioning but are not accurate
enough for precise location management. GPS receivers
used for DGPS, however, are inexpensive. In addition, in
Japan, DGPS service that uses FM multiplex broadcasts
for vehicle-mounted navigation systems is a-vailable in
almost all parts of the country. Consequently, in areas
within range of the FM multiplex broadcasts, DGPS
positioning can be carried out relatively inexpensively.
Another advantage of DGPS is that extreme deterioration
of accuracy does not occur even when satellite trans
missions or correction data transmissions are interrupted
under the influence of the surrounding topography: sys
tem operation returns to normal immediately after com
munications are reestablished.
The set-up for RTK-GPS is similar to DGPS, as shown in
Figure 4: a GPS receiver is set up at a known location and
at a measurement location. In the case of RTK-GPS,
however, information transmitted to the measurement
location is not correction information but GPS satellites'
Figure.3 Differential GPS (DGPS)
observation information obtained from measurement at
the known location. At the measurement location, this
information is used to calculate the measurement location
through baseline analysis between the known location
and the measurement location. The positioning accuracy
of RTK-GPS is several centimeters (about 2 cm in the
horizontal direction and about 5 cm in the vertical
direction), which is high enough for precise location
management. Since, however, RTK-GPS receivers are
more expensive than DGPS receivers, an RTK-GPS-
based rolling management system is more expensive
than a DGPS-based system. Another disadvantage of