hello the article about gps is for your reference
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An Introduction to GPS

GPS is now widely applied for car, outdoor, fitness, specialty and cell phone, etc. It receives signals from GPS satellites, and the quality of signal is determined by many factors, like solar radiation, atmosphere conditions and terrain.

Generally not all signal from the satellite gets through to your GPS, the signal scattering is usually from vegetation, sometimes from terrain, buildings, or other objects between you and GPS satellite.

There are a lot of styles for GPS receiver in the market, including car GPS, general outdoor GPS, fitness GPS, specialty GPS and cell phone GPS.

General Outdoor GPS

Outdoor GPS is widely used in outdoor activities like hunting, travelling, climbing, etc. It is well designed to fit in the palm of your hand with integrated electronic compass and barometric altimeter, some applies touch screen and integrated camera.

An electronic compass functions like a real compass, with the electronic compass, you not only know the direction you are heading for, but also know the specific location.

The barometric altimeter is to determine altitude by air pressure, its accuracy rests on calibration frequency and weather. The weather condition will cause the barometer to show slightly higher or lower elevations, but calibrating more often at known elevations can minimize error.

Fitness GPS

Fitness GPS is mostly used to record the progress of exercises. It records important data in exercises and track improvement. Some includes a heart rate monitor, with which you can track heart rate according to elevation, speed and so on. With separate devices, it is difficult to relate the two kinds of data. Besides, some cycling receiver includes a cadence sensor to collect cadence data. Fitness receivers also have option to report elevation values with a barometric altimeter.

Car GPS

Car GPS navigation system is a very hot electronic device to the market these years, it can tell you where you are, how to reach the destination, choose the shortest or fastest route. Thus, you can avoid the traffic jam and go down the right path.

Additionally, some car GPS supports Bluetooth technology so that you can use the GPS in conjunction with your cell phone, reports traffic and weather instantly, plays audio files.