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