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Appendix
Simple hybrid mode
When the speed pulse is not detected, position-
ing is performed in this mode. Only horizontal
movement is detected, so it becomes less accu-
rate. Also, when the positioning by GPS is not
available, such as when your vehicle enters a
long tunnel, the discrepancy between your actual
and calculated position may become bigger.
❒ The speed pulse data comes from the speed
sensing circuit. The location of this speed
sensing circuit depends on your vehicle
model. In some cases, it is impossible to
make a connection to it, and in such a case
we recommend that the ND-PG1 speed pulse
generator (sold separately) be used.
How do GPS and dead reckoning work
together?
For maximum accuracy, your Navigation System
continually compares GPS data with your esti-
mated position as calculated from the data of 3D
Hybrid Sensor. However, if only the data from the
3D Hybrid 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 avail-
able, they are matched with the data of the 3D
Hybrid Sensor and used to correct it for improved
accuracy.
To ensure maximum accuracy, the dead reckon-
ing system learns with experience. By comparing
the position it estimates with your actual position
as obtained using GPS, it can correct for various
types of error, such as tire wear and the rolling
motion of your vehicle. As you drive, the dead
reckoning system gradually gathers more data,
learns more, and the accuracy of its estimates
gradually increases. So, after you have driven
some distance, you can expect your position as
shown on the map to show fewer errors.
❒ If you use chains on your wheels for winter
driving, or if you put on the spare wheel, the
errors may appear to suddenly increase
because of the increased wheel diameter. The
system detects the fact that the tire diameter
has changed, and automatically replaces the
value for calculating distance.
❒ If the ND-PG1 is used or if your vehicle is oper-
ating in Simple hybrid mode, the distance cal-
culation value cannot be replaced
automatically.
Map matching
As mentioned, the GPS and dead reckoning sys-
tems used by this Navigation System are suscep-
tible to certain errors. Their calculations may, on
occasion, place you in a location on the map
where no road exists. In this situation, the pro-
cessing 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.
Handling Large Errors
Positioning errors are kept to a minimum by com-
bining GPS, Dead Reckoning, and map match-
ing. However, in some situations, these functions
may not work properly, and the error may
become bigger.
When the positioning by GPS is
impossible
• If signals cannot be received from more than
two GPS satellites, GPS positioning does not
take place.
• In some driving conditions, signals from GPS
satellites may not reach your vehicle. In this
With map matching
Without map matching