Satellite Navigation

Guide to In-Car Satellite Navigation

Introduction to Satellite Navigation

If you do a lot of driving, or simply enjoy your gadgets, the latest and most popular accessory for your car is an in-car satellite navigation system. These receivers tell you where you are and show you where you're going. You enter the location you want to go to and the software works out a route and displays it on a map on-screen. Your current position is marked on the map which updates as you go. They usually provide turn by turn directions and some use digital voices to tell you your next move. Some even allow you to change the voice to that of a popular celebrity. You could have Tony Blair telling you how to get to the airport if you wish! Whatever system you choose, you should never get lost again!

These in-car satellite navigation systems or Sat Nav as it is often abbreviated to, use GPS (Global Positioning System) technology. This technology is a way to determine location based on signals beamed from a network of over 20 satellites which are in six orbital paths around the Earth. A GPS unit tracks the speed of each satellite and compares it relative to the unit's location, therefore calculating the unit's latitude, longitude, and altitude

This technology was originally meant to be only used for military purposes but has now been opened up for civilian use.

How In-Car Satellite Navigation Works

Each of the 24 satellites orbit the Earth twice a day, travelling at approximately 7,000 miles per hour. They orbit at about 12,000 miles above the Earths surface and they are positioned so that least four of them are visible in the sky at any time.

For a GPS receiver to work, it must be able to receive the signals from at least three different satellites. The more satellites it can track, the more accurate its positioning will be. Most GPS devices track three or four satellites at a time. They are usually accurate to within 3 or 4 metres.

All car-based Satellite Navigation GPS systems enter your location into map files stored in the receiver's memory. This specifies your location on the map, and means that the software can calculate distances and directions to other locations that you enter.

Using the map information the receiver will track your path on the map as you move. It will also calculate routes to locations that you enter, following the roads that are in the electronic map. The best route to your desired location is displayed on the map, and route instructions are either displayed or "said" out loud by a computer-generated voice. Following these instructions your GPS system will guide you to your destination. Remember though to keep your eyes on the road!

Other Satellite Navigation Features

The software usually tracks other driving data. You'll be able to find out how far you've travelled, how long you've been driving and average speed information. It can also tell you when you are expected to arrive at your destination. Everything is done automatically; just enter the address of your destination. Most will accept post codes as destinations.

Many GPS devices enhance their map data with preprogrammed points of interest. These include petrol stations, restaurants, motorway services, cash machines etc. It really takes the guesswork out of travelling!

Types of Satellite Navigation Receivers

Most in-car Satellite Navigation systems come with either windscreen or dashboard mounts and can be independently battery powered, or connect to your cars power via a cigarette lighter or the DC power outlets increasingly found in modern cars.

The best of the car GPS systems let you read the route instructions on the display or hear them from a computer-generated voice. This option is particularly useful as you don't have to take your eyes off the road, but if you don't want to listen to the voice instructions they can be turned off.

There are different types of displays offered by various devices. Generally you have a choice of traditional overhead-view 2D maps or text instructions, although many of the newer models have 3D maps.

The other big difference between the various devices is whether the maps and points of interest are preloaded onto the device's hard drive or have to be downloaded from your computer (using media cards or CD's) as you need them. The advantage of preloading is convenience, of course; the advantage of load-as-you-go systems is that you can download updated maps as they become available. In any case, make sure you get adequate map coverage for whatever regions you frequently travel.

Other features to look for are portability, which lets you take the system with you when you change cars, audible notification when you are coming to a turn or junction and the ability to quickly recalculate your route if you take a wrong turn. Also make sure you're comfortable with the size and clarity of the display.

One final point - make sure that your in-car satellite navigation system is removed from the vehicle or completely concealed from view when you leave your car. They are becoming the latest piece of hot property on the black market and thieves will steal them immediately if given the opportunity.