Appendix
Appendix
51
Engb
Appendix
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
21 000 km, continually broadcasts radio signals
giving time and position information. This en-
sures 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 sig-
nals 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.
Handling large errors
Positioning errors are kept to a minimum by
combining GPS, dead reckoning and map
matching. However, in some situations, these
functions may not work properly, and the error
may become larger.
When positioning by GPS is
impossible
GPS positioning is disabled if signals cannot
be received from more than two GPS satel-
lites.
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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 re-
ception of GPS signals. Snow buildup can al-
so degrade the signals, so keep the aerial
clear.
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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 updat-
ed. In such a case, once GPS reception is re-
stored, accuracy will recover.
Conditions likely to cause noticeable
positioning errors
For various reasons, such as the state of the
road you are travelling on and the reception
status of the GPS signal, the actual position of
your vehicle may differ from the position dis-
played on the map screen.
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