About Garmin GPS Systems

Handheld GPS receivers are commonplace today. Most cell phones feature at least emergency GPS locating devices and the popularity of Garmin GPS receivers for recreational use has increased with the advent of geocaching. GPS devices can not only tell you where you are, but also guide you to the desired location.

History

In 1978, the first experimental GPS satellite was launched. By 1994, a network, or constellation, of 24 satellites had been launched into orbit. In 1996, President Clinton issued a directive stating that the GPS satellites were a dual-use system (for civilians as well as military) however the regular public continued to receive a degraded signal until 2000 when the previous selective availability was stopped, and everyone worldwide could receive a non-degraded signal.

Function

The primary function of the Garmin GPS is as a navigating tool. By picking up satellite signals the GPS device is able to triangulate the your location. The GPS device can help guide you to particular location as seen with Garmin's automotive navigational system and the handheld Garmin receivers used by hikers. Garmin GPS can also be used to calculate sunrise and sunset, altitude and the speed at which you are traveling.

Features

Most Garmin GPS systems are only accurate to within a distance of 15 meters. However, newer Garmin GPS receivers also come with Wide Area Augmentation Systems (WAAS). WAAS features a series of satellite and ground stations that are capable of correcting the GPS satellite signal, thus increasing accuracy to as little as three meters. Differential GPS is another form of correctional system used by Garmin GPS receivers and corrects the signal to an accuracy of within three to five meters.

Geography

The process by which a GPS receives its information and calculates a location is called trilateration. There are 24 satellites that orbit the earth, circling twice daily. The Garmin GPS receiver receives the signal from the satellite and compares the time that the satellite sent the signal to when it was received by the GPS receiver. That is how the GPS receiver calculates the distance. In trilateration, the GPS gets information from satellite A stating that it is 10 miles away. The GPS now knows that it is located within a sphere with a 10 mile radius from satellite A. A second satellite signal says the GPS is 15 miles away from satellite B. The receiver has to be located somewhere in the area that these two spheres converge. To further triangulate, the receiver gets a third signal that says the receiver is 5 miles away from satellite C. Where satellite A, B and C spheres converge is where the receiver is located. With the use of three satellites, the Garmin receiver can locate its longitude and latitude. A fourth satellite will locate the receiver's altitude.

Considerations

While Garmin GPS' are typically highly accurate, certain conditions can cause inaccuracies. If the satellite is traveling through the atmosphere it can cause ionosphere and troposphere delays, because the signal from the satellite is slowing as it passes through the atmosphere, however the GPS system does have a way to correct for these slight inaccuracies. Additionally, factors such as dense foliage and electronic interference can cause the GPS receiver to not see the satellites' signals.