The global positioning system (GPS) was developed by the US Department of Defense and is officially known as NAVSTAR GPS. Initially, the global positioning system was available only to the US military and government, but after a period of time the system was made available for commercial use. Today, GPS is used by people from all walks of life and advances in technology have made possible integration of GPS receivers into all types of handheld devices, even modern day cell phones come equipped with GPS receivers. To better understand GPS, it is important to understand how GPS works.



There are currently 27 NAVSTAR satellites orbiting the globe, only 24 of these satellites are currently in use (the remaining 3 are backups if any satellite fails). Each satellite is positioned at an altitude of 12,000 miles from the earth and makes two complete rotations every day. These satellites have been positioned so that, at any given time there are at least 4 satellites ?visible? in the sky. A GPS receiver uses a process called trilateration to calculate the exact position of a person.

To better understand the process of trilateration lets start with a simple example. Let's assume you are located at a point X on the planet, your GPS receiver is actively receiving signals from at least 3 GPS satellites at any given time. A GPS receiver calculates the exact position of a person by using the signal strength from each satellite to narrow down the position. Say there are three satellites A, B and C from which the GPS receiver is receiving signals. By using the distinct signals the GPS receiver calculates the distance of the three satellites from the earth as well as from each other. The final coordinate calculation is not a simple one and is a series of complex results, but the end result is that the GPS receiver can effectively pinpoint the exact location in terms of longitude and latitude.

What is equally impressive about GPS is that each NAVSTAR satellite is equipped with an atomic clock to synchronise it with other satellites. The GPS receiver constantly resets its clock to stay in sync with GPS satellites. So, not only does the GPS system give you your location, but it also gives you the most accurate time on the planet!

GPS might seem fool proof, but factors like the earth's atmosphere and heavy cloud cover actually put off the calculations of a GPS receiver. To make the readings even more accurate, a GPS receiver uses signals from a stationary GPS receiver station. A stationary GPS receiver station already knows its precise location, so a GPS receiver can utilize the signals from a receiver station to correct any errors. This technique of calculating coordinates is known as differential GPS and almost all commercial GPS receivers available in the US come equipped with differential GPS.

The leading GPS device manufacturer today is Garmin. Garmin has one of the most comprehensive ranges of GPS devices and also makes quality GPS navigation devices. To buy Garmin GPS devices visit www.outdoorsman-essentials.com.

How GPS navigation devices work

A traditional GPS device only calculates the co-ordinates in terms of latitude and longitude. Since differential GPS allows for pinpoint accuracy, it is now possible to display the exact location of a person on a map by juxtaposing the co-ordinates with known co-ordinates. GPS navigation devices today offer features like choosing the best route to a destination, detailed route maps, calculating the distance already travelled and also the popular ?bead crumb trail? that shows the exact path traversed. Contrary to popular belief, GPS navigation systems only have a limited number of maps stored into them, and additional maps have to be fed into the device's memory. If the GPS navigation system does not have a map it cannot offer more than just the GPS co-ordinates.