Car owners guide to: Satellite Navigation > In-Car Sat Nav
 Portable
Sat Nav devices can be a good choice if you find yourself having
to hire cars at home or abroad, or if you have to drive a variety
of vehicles in your job, as they allow you to carry the device from
car to car. However, they fall short in matching the accuracy, ease
of use, display clarity (especially on road junctions) and cosmetic
integration of the dedicated In-Car Navigation devices.
If you've read our short introduction to Satellite Navigation you
will know that these devices make use of the Global Positioning
System to calculate the position of your vehicle with a good degree
of accuracy. As long as the car navigation receiver can read the
position of at least three satellites, then by a process of mathematical
triangulation it can work out where you are.
GPS is at the core of nearly all these devices, but added features
improve both the accuracy and useability of navigational aids in
the car, and it's these features that set apart the various types
of Sat Nav devices now on the market.
Fixed or 'embedded' Sat Nav systems
Most fixed In-Car Satellite Navigation systems consist of a miniature
computer connected to a CD, DVD or Data Card reader; a gyroscope;
and a GPS receiver and antenna. A feed from the vehicle's electronics
known as the 'speed pulse' supplies additional data to the navigation
computer. The speed pulse feed and gyroscope are features that considerably
improve the accuracy and reliability of fixed Sat Nav systems compared
to the portable devices.
The fixed systems tend to have large, high-quality displays, often
touch-sensitive and fold-away. This allows the device to neatly
fit into the same space as a conventional in-dash CD player. Most
will come with a remote controller and sophisticated mapping with
advanced search facilities and a huge number of Points of Interest
(POI) - these are useful places like petrol stations and bank ATMs,
and leisure spots such as restaurants.
Inputting your destination is easy, either by speaking the pre-assigned
name you've given to the address, or by entering the address or
post code on the remote control, or by touchscreen. They all support
the screen instructions with clear spoken directions delivered through
the vehicle's own speaker system for best clarity.
Most fixed car navigation systems can also retrieve and decode
realtime traffic information (via a TMC data feed - TMC stands for
Traffic Message Channel) and automatically re-route you around traffic
trouble spots.
Systems that use CD or DVD to deliver their mapping data will usually
double as an entertainment system. Once the required mapping data
is read into memory for a particular route or area, the reader is
free to play other discs.
All-in-all these are the most accurate and easy-to-use Sat Nav
systems for the car, but they do require professional installation.
They are relatively expensive, but don't forget that in most cases
you're also getting a CD or DVD player for entertainment too. And
the whole system will fit perfectly into your car's environment
- no trailing cables, no ugly and sometimes unreliable mounting
brackets.
How does the Sat Nav benefit from the Speed Pulse feed and Gyroscope?
These are the two most significant aspects of fixed In-Car Sat
Nav systems that set them apart from the portable devices in getting
you from A to B with minimum fuss.
Receiving speed pulse information from the engine management system
(or a speed pulse generator in the case of some older or diesel
vehicles), allows the navigation device to know how far along the
road the car has travelled.
Of course the triangulation of the satellite signals will allow
the device to track the vehicle, as long as it can see the satellites,
but having the speed pulse information provides even greater accuracy.
And if the vehicle passes through areas where vertical visibility
is restricted, such as between highrise buildings or steep hillsides,
you won't be left stranded.
While the speed pulse data tells the system how far the vehicle
has travelled, the Gyroscope provides information on which direction
you're headed. Again, this gets added to the data from the satellites
or, if there's no line of sight to the satellites, then the data
from the Gyroscope and speed pulse does a good job of tracking you
on the digital map until satellite reception is restored.
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