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Buyers Guides > Getting the most from your GPS Satellite Navigation System

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Introduction

GPS or "Global Positioning System" devices rely on transmissions from a "constellation" of satellites; 24 in total, of which up to 8 may be "visible" from the surface of the Earth at any one time, placed into orbit by the U.S. Department of Defence. A GPS receiver requires signals from 3 satellites, 4 if altitude or elevation is to be calculated, and uses a process known as "triangulation" to calculate its own position on the surface of the Earth to within 50' or less in many cases.

GPS receivers usually feature a display of some kind, typically a large 3.5" or 4.3" colour LCD ("Liquid Crystal Display"), on which a map and/or visible directions are displayed, along with a number of various options. Most GPS receivers similarly have a programmed "voice" or possibly a selection of voices, so that directions can be delivered audibly as well as, or instead of, visibly. This can be a boon for drivers meaning that the screen itself, need not be a distraction.

A GPS receiver has obvious advantages over a traditional road map or road atlas, in terms of accessibility and convenience, but also offers the benefits of route planning according to your own personal preferences, and the ability to change your route based on traffic congestion, and other causes of delay. If you frequently travel into unfamiliar areas (rural areas in particular) where meaningful landmarks, and road signs are often in short supply, a GPS device is often the only effective means of navigation.

GPS Satellite Navigation Tips, Tricks & Techniques

GPS Locks

When a GPS device is switched on, particularly when switched on for the very first time, it downloads so-called "almanac" information from each of the GPS satellites that it will use to calculate its location. It may take anything up to 30 seconds for the data from each satellite to be received, completely error-free, and if a GPS receiver is moving around or obstructed by trees, buildings, etc., many retries may be necessary to receive this information accurately. This extends the TTFF or "Time to First Fix" considerably, and in some cases may result in erroneous calculations that are inaccurate by anything from a few feet to a mile or so. The accepted procedure for downloading this information efficiently and accurately to a GPS device is to leave the device powered on, but motionless, under an open sky for a period of 20 minutes or so. This procedure needs to be applied the first time that you turn a GPS unit on, but can also be useful during the lifetime of a unit, if the acquisition of satellite signals becomes noticeably slow.

Waypoints

A waypoint is quite simply, any location that you store in a GPS receiver; it could be for example, your home, a landmark, or even something as ordinary as a motorway service station, and may be referred to in your GPS documentation as "landmark", "location", or "favourite", but all waypoints are effectively treated in the same way.

GPS software typically maintains the latitude, longitude and elevation of each waypoint, along with other information such as the date and time when it was created. You can usually create a waypoint by marking your current location if it is somewhere that you wish to return to, or from previously saved coordinates or from a collection of waypoints available from the Internet. The precise method of creating, and editing, waypoints may vary from GPS receiver to GPS receiver, but typically each can be given a unique name or icon such that it can be easily identified.

While it may be tempting to create waypoints for your home, work, and anywhere you go on a regular basis, if your GPS is set to direct you along the quickest route, you may find new ways of driving to these familiar places, and make some fuel savings as a result. Do remember that, while it may be possible to create a hundred or more waypoints, there is a finite limit. You should therefore, only really create waypoints at locations where you require direction. The downside of this of course, is that GPS receivers do tend to display the straight line distances between waypoints, so the more waypoints you create the more accurate distance measurements are likely to be. If you do require additional waypoints, create them without supplementary information such as comments, to save space. If you are travelling a specific familiar route, it may also be possible to direct a GPS unit via its interface, to ignore waypoints other than your starting point and destination, as a means of saving you distance and time.

Audible Directions

Many GPS receivers provide the facility to listen to audible directions (and possibly mobile 'phone calls, or MP3 music) through the existing loudspeakers in your car, rather than an inferior speaker on the GPS unit itself. An FM transmitter allows a GPS receiver to transmit signals on any unused frequency – generally easy to locate in rural areas, but perhaps more challenging in urban environments, where the FM frequency band is more crowded, and these can be received and played back on a conventional car audio system. Another alternative of course, is to physically connect a GPS unit; via its headphone or "audio out" jack, to the auxiliary input of your car audio system.

Batteries

Many GPS devices are supplied with AC and 12-volt DC charging options, and rechargeable batteries. Battery life generally speaking is limited to between 2 and 3 hours however, so it is advisable to use a power source, rather than the battery, wherever possible, and to save the batteries for emergencies or unforeseen circumstances (in a car, or elsewhere) where battery power is the only option, for whatever reason. Bear in mind that optimal performance of a new rechargeable battery can often only be achieved after two or three, complete charge and discharge cycles. Overcharging may shorten the life of a rechargeable battery, as may subjecting it to extremes of temperature; by leaving it in a car during the summer or winter, for example, and in any case, a rechargeable battery can only be charged and discharged a finite number of times.

Security

GPS units are obviously highly desirable, and not only with consumers who acquire them by legitimate means; thieves are on the lookout for units left in unattended cars, or the marks left by the suction cups used to secure units to the windscreen, which often indicate a GPS unit in the glove compartment, so it is wise to take some security precautions. It is advisable to remove a GPS unit from your car every time it is to be left unattended, and to remove any trace of mounting, by wiping away any marks. Friction mounting, with a weighted mount that can be easily be hidden in the glove compartment, or under a seat, and leaves no marks, may be a useful alternative if taking a GPS unit with you is impractical. Furthermore, however tempting it may be, do not enter the full postal address of your home into a GPS unit; if your GPS unit does fall into the wrong hands, this information effectively gives a thief carte blanche to burgle your home at a time when they know that you are not there.

Practice Makes Perfect

If you are a "professional" driver, and you intend to rely on a GPS receiver to provide you with accurate directions for work, or any other critical purpose, it is advisable to run through the procedures for operating the equipment; determining your position, creating waypoints, etc., before you need to do so in a "real life" situation. It pays to read the manual, and familiarise yourself with the basic functions, either in "simulator" mode which some units allow, or in "live" mode, during your journey to work for example, so that you can be sure that your GPS unit is functioning correctly, when you really need it, and simply get used to its presence, visibly and/or audibly, in your car. ervices Authority") offers information on preparing for retirement, insurance policies, etc., and much more content from many more providers is likely as other bodies embrace the new technology.