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Some types of vehicles may not output a speed signal while
driving at just a few kilometres per hour. In such a case, the
current location of your vehicle may not be displayed cor-
rectly while in traffic jam or in a car park.
How do GPS and dead reckoning
work together?
For maximum accuracy, your navigation system continually com-
pares GPS data with your estimated position as calculated from
the data of built-in sensor. However, if only the data from the
built-in sensor is available for a long period, positioning errors
are gradually compounded until the estimated position becomes
unreliable. For this reason, whenever GPS signals are available,
they are matched with the data of the built-in sensor and used to
correct it for improved accuracy.
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If you use chains on your wheels for winter driving or put on
the spare wheel, errors may suddenly increase because of
difference in wheel diameter. Initialise the sensor status and
it may recover the accuracy to normal condition.
For details, refer to
Clearing the status
on page 56.
Map matching
As mentioned, the positioning systems used by this navigation
system are susceptible to certain errors. Their calculations may,
on occasion, place you in a location on the map where no road
exists. In this situation, the processing system understands that
vehicles travel only on roads, and can correct your position by
adjusting it to a nearby road. This is called map matching.
With map matching
Without map matching
Handling large errors
Positioning errors are kept to a minimum by combining GPS,
dead reckoning and map matching. However, in some situa-
tions, these functions may not work properly, and the error may
become bigger.
When positioning by GPS is
impossible
GPS positioning is disabled if signals cannot be received
from more than two GPS satellites.
In some driving conditions, signals from GPS satellites may
not reach your vehicle. In this case, it is impossible for the
system to use GPS positioning.
In tunnels or enclosed parking garages
Under elevated roads or similar structures
When driving among high buildings
When driving through a dense forest or tall trees
If a car phone or mobile phone is used near the GPS aerial,
GPS reception may be lost temporarily.
Do not cover the GPS aerial with spray paint or car wax,
because this may block the reception of GPS signals. Snow
buildup can also degrade the signals, so keep the aerial
clear.
p
If a GPS signal has not been received for a long time, your
vehicle’s actual position and the current position mark on
the map may diverge considerably or may not be updated. In
such case, once GPS reception is restored, accuracy will be
recovered.
Conditions likely to cause noticeable
positioning errors
For various reasons, such as the state of the road you are trav-
elling on and the reception status of the GPS signal, the actual
position of your vehicle may differ from the position displayed on
the map screen.
If you make a slight turn.
Positioning technology
Positioning by GPS
The Global Positioning System (GPS) uses a network of satellites
orbiting the Earth. Each of the satellites, which orbit at a height
of 68 900 000 feet (21 000 km), continually broadcasts radio
signals giving time and position information. This ensures that
signals from at least three can be picked up from any open area
on the earth’s surface.
The accuracy of the GPS information depends on how good the
reception is. When the signals are strong and reception is good,
GPS can determine latitude, longitude and altitude for accurate
positioning in three dimensions. But if signal quality is poor, only
two dimensions, latitude and longitude, can be obtained and
positioning errors are somewhat greater.
Positioning by dead reckoning
The built-in sensor in the navigation system also calculates your
position. The current location is measured by detecting driving
distance with the speed pulse, the turning direction with the gyro
sensor and inclination of the road with the G sensor.
The built-in sensor can even calculate changes of altitude, and
correct the discrepancies in the distance travelled caused by
driving along winding roads or up slopes.
If you use this navigation system with connecting the speed
pulse, the system will become more accurate than no connec-
tion of speed pulse. So you connect the speed pulse without fail
to get the accuracy of positioning.
p
The position of the speed detection circuit vary depending
on the vehicle model. For details, consult your authorised
Pioneer dealer or an installation professional.
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< CRB4783-A >
Appendix
Appendix
