137
AppendixNAVI/AV
Map matching
As mentioned, the GPS and dead reckoning sys-
tems used by this navigation system are suscepti-
ble 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 matching.
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
case, it is impossible for the system to use GPS
positioning.
With map matching
Without map matching
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
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