Car owners guide to: Satellite Navigation (Sat-Nav)
 Thanks
to cheaper production and falling prices of portable devices, 'Sat
Nav' became the latest high-tech "must have" for UK consumers
in 2005. The demand gave rise to a big choice of models available
from a variety of mostly non-specialist retailers, and at ever more
appealing prices.
The more sophisticated fixed or "embedded" in-car navigation
systems have also come down in price but have nonetheless remained
very much in the "serious user" bracket. These fixed Sat
Nav systems offer a number of benefits over the portable devices,
whilst losing out on the one big advantage of the latter - their
portability and therefore ability to be moved from car to car, from
yours to your partner's car, a hire car or a friend's car.
GPS Satellite Navigation - how does it work?
Global Positioning satellites are constantly circling the Earth
(GPS stands for 'Global Positioning System'). Each follows a set
path and speed around the globe and therefore, at any particular
time, each satellite will be at a very precise location in the sky.
Signals being constantly beamed to Earth from each satellite can
be read by receiving equipment down below to very precisely position
objects on the ground.
As long as the satellite receiver on the ground can read the position
of at least three satellites, a process of mathematical triangulation
allows it to calculate its own location. Portable Sat Nav devices
generally rely entirely on GPS positioning technology along with
sophisticated digital mapping.
The navigation device receives enough information from the satellites
to provide a relatively accurate position on the ground, but digital
mapping and some clever software is needed to synchronise the satellite
signals and correct for slight errors. In this way, the Sat Nav
device will show you on the road even if the satellite signals would
have you motoring through the houses 30 feet to your right!
Most fixed In-Car Navigation systems will also include a gyroscope.
This adds extra accuracy and becomes especially useful whenever
satellite reception is impeded. The fixed systems also use a separate
antenna that can be positioned for best reception. With the portable
devices, it may be necessary to buy and mount an additional antenna
if your vehicle has a heated or reflective windscreen.
In all cases, there is an ongoing cost to Sat Nav in the form of
updated maps. Apart from any specific rental offers, there's no
recurring cost - the maps you get are yours to keep and use for
as long as you like - but of course new roads are built, roundabouts
are added, road priorities change, and new postcode areas are added.
You should ideally replace your map discs every couple of years,
and the cost can be anything from £100 to over £400.
The GSM human-assisted option
There is another option which keeps the map centrally located and
all you have in the car is a button on the dashboard which, when
pressed for two seconds, connects you via GSM (mobile phone) with
an operator who can talk plain English with you. He or she will
send the journey plan to the box in your car by phone. You are then
guided to your destination by very accurate voice instruction.
The annual subscription on this type of navigation equates to about
the same as the CD-based Sat Nav units. The big plus is that the
map is always up to date. This system also takes into account traffic
jams and can be made to alert you to the location of speed cameras.
Its use of the GSM phone system also allows the operator to assist
in finding your vehicle if it has been stolen.
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