GPS Basics
What is GPS and how does it work?
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What is GPS?
Global Positioning System (or GPS as it’s better known) is essentially a technology that allows a suitably equipped receiver to pinpoint its position anywhere on the planet’s surface. Over the last 12 years it has had a major impact in navigational systems for everything from walkers to pilots.
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The Colorado 300
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How GPS works
Satellites orbit the Earth at a height of around 11,000 miles and send a stream of radio signals out identifying their exact position. By knowing how far away you are from 4 or more satellites and how far the satellites are away from each other your receiver can work out where you must be.
The 24 satellites of the original system are divided to give complete cover of the whole planet, so 12 satellites cover each hemisphere at any one time.
A minimum of 6 satellites should be within radio signal range and direction at any time. For a good location fix a minimum of 4 satellites signals are required, the more satellites that are ‘visible’, the greater the degree of accuracy.
Software within a GPS receiver takes the signals from each satellite and through triangulation converts the signals into longitude, latitude and elevation. This information can then be converted into a useable format of either a text or graphical display and related to a map.
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Limitations of GPS
It’s important to remember that GPS itself is NOT a mapping solution, but merely a triangulation system that gives your position in relation to a system of orbiting satellites. This position is then translated, to varying degrees of accuracy, to a position on a map by a separate software application.
GPS is not a replacement for the traditional hill walkers’ skills of map and compass use, but is an additional resource that may be used either on its own or in combination with these traditional skills.
It is important to remember that your personal safety is your own responsibility at all times, and whilst GPS is a useful tool it should not be relied on as the sole means of navigation in the outdoors.
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Does GPS work everywhere?
Because the system uses radio waves, the ability to receive a signal is partially dependent upon the surrounding environment, although increases in the sensitivity of the receivers are improving this situation. Dense woodland, tall buildings, and canyons in particular can make reception difficult or reflect the signal giving a false reading.
The recent SiRF III chipsets have gone a long way to reducing this problem and a GPS receiver based around this chipset should be suitable in almost any outdoor location – and even indoors within reasonable distance of a window or line of sight. Despite the advances in chipset sensitivity, Ionospheric distortion, caused by high solar activity, can cause dramatic malfunctions by slowing the progress of the radio signals through the ionosphere.
This is one of the reasons why GPS is not a total replacement for map and compass skills.
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GPS Basics
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Getting Started
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GPS Buyer's Guide
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Using Your GPS
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GPS and Your PC
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