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Car GPS Navigation Systems - A Buyers Guide
In 1973 the U.S. Department of Defence launched the Navstar GPS network.
This consisted of 24 satellites orbiting the earth every 12 hours and
five ground stations. This positioning system was made available for
public use. With this capability, consumer location devices were produced
to accurately determine location and other data such as current and
average speed, directional heading, and elevation. These GPS devices need
an unobstructed view of at least four satellites to provide a reliable 3D
fix.
The GPS receiver overlays this location data onto map files stored on the
unit, to give a current position on the map as well previous track. The
receiver constantly recalculates position, giving real time position.
A typical GPS device contains:
* 12-channel receiver - the quality of the receiver determines how long
it takes the device to acquire a 3D fix.
* Antenna to capture satellite signals - positioned to get a clear view
of the sky.
* CPU to process the data and overlay on maps
* DVD Hard-drive - where maps on DVD's or available online are uploaded
and stored. Some cheaper units do not upload the maps, but reference
them off the DVD or CD.
* Display Screen - mostly color with handheld units using black and
white
* Voice Interface - more advanced units
How The GPS Device Gets A Fix
The first time you start your GPS device, its data store is blank so
needs a to collect satellite information to determine your position. This
is known as a cold start. Some units only take 30 to 45 seconds to
acquire a 3D fix during a cold start, while others can take several
minutes. Subsequent position updates only take 3 to 4 seconds. If you go
out of range from losing line of sight, such as passing behind a large
building or through a tunnel, a good receiver will instantly recover,
whereas weaker units will require more time to reacquire a 3D fix.
How Different GPS Navigation Units Differ
Location of Antenna - A factory installed in-dash unit antenna is
integrated into the dashboard where it has an unobstructed view of the
sky. Many portable models have a suction-cup-mounting device to position
the device on the windshield. Add-on antennas are also available.
Regardless of the type of unit and antenna, the important thing is to
keep the antenna visible to the greatest area of sky possible. Choose a
unit where this can be done AT THE SAME TIME as being able to maintain a
clear view of the screen.
Screens and Display - important to check how bright these are, and if
they are clearly visible from the mounted position in bright day light.
Onboard navigation systems are generally color screens, and portable
units are black and white to save power. Larger screens and integrate
better with other vehicle electronics.
Input Buttons - most enroute buttons are on the display screen. Ensure
these are easy to use when driving; that is they are big enough and
colored sufficently to see without causing a driving hazard.
Map Media - Earlier models were CD-based, requiring multiple discs to
cover the entire United States. Newer in-dash systems are DVD-based; only
1-2 DVD's required for an entire country of maps.
Cost - In-dash systems are usually more expensive than portable
counterparts. Aftermarket in-dash models usually require professional
installation and can be just as expensive as the factory models.
Upgrading - always check how easy it is to upgrade the firmware and maps
on your GPS unit. Some units detach a portion to be connected to the
computer via USB, whereas others are done using a DVD. Those units which
can be upgraded online, are much more convenient.
Added Features of GPS Units
Apart from giving you a current position, a number of GPS navigation
devices can give you:
* A track of where you have been - the number of tracks and waypoints
stored varies from unit to unit. You may also want to save on part of a
track for future use.
* A path from your current position to your destination
* Maintain commonly used navigation paths for reuse.
* Points of Interest - user sets the types of points of interest, such
as tourist, bank ATM, petrol stations, historical, accommodation,
restaurants etc.
* Real time traffic reporting to avoid traffic delays. This can also
include road works.
* Voice recognition to receive destination instructions, and voice
guidance to give driving instructions
* Weather updates
* Street name navigation - instead of just turn left 200m it was say
'Turn left into Stanley St'
* Integrated Multimedia players - MP3 players, image viewers, and audio
books.
* Onboard or Portable GPS Navigation
The downside of onboard GPS Navigation units are susceptible to theft;
and you cannot take them with you to use in other vehicles or when
travelling abroad. Portable units, such as the Garmin StreetPilot 2720,
can be used in multiple cars; being easily moved from car to car.
Depending upon the power supply and portability, portable and handheld
units can be taken when travelling or used on cycles, boats, private
aircraft etc. For more information on Car GPS Navigation Systems
About the Author
Nicola Carr is a technology strategist and publisher of Go-Reviews.com.
She provides product reviews and buying guides on a wide range of
technology. She is also a feature writer for Electrosmart Digital
Publishing and RichMediaMix demonstrating how technology is integrating
into business and media.
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