Global Positioning System (GPS) is a satellite-based navigation system consisting of at least 24 satellites. GPS works in all weather conditions, anywhere in the world, 24 hours a day, without subscription fees or setup fees. The US Department of Defense (USDOD) originally put satellites into orbit for military use, but they were made available for civilian use in the 1980s. However, today GPS is being used for daily conveniences instead of military, so it can even be used for businesses, like the geo fencing service.
GPS satellites circle the Earth twice a day in the right orbit. Each satellite sends unique signals and orbital parameters that allow GPS devices to decode and calculate the exact location of the satellite. The GPS receiver uses this information and trilateration to calculate the user’s exact location. A GPS receiver measures the distance to each satellite with the amount of time needed to receive the signal being sent. By measuring distances from several more satellites, the receiver can determine the user’s position and display it electronically to measure your running route, map golf courses, find your way home or adventure anywhere.
To calculate your 2-D position (latitude and longitude) and track movements, the GPS receiver must be locked to a signal of at least 3 satellites. With multiple satellites, the receiving end can determine your exact 3-D location. (latitude, longitude, and altitude). Generally, a GPS receiver will track 8 or more satellites, but that depends on the time and where you are on earth. Some devices can do all that from your wrist.
After your position is determined, the GPS unit can calculate other information, such as :
Distance to destination.
Sunrise & Sunset.
and more so.
The current GPS receiver is very accurate, thanks to its parallel multi-channel design. Our receiver quickly locks it to the satellite when it is first turned on. They retain the tracking key in dense trees or in urban environments with tall buildings. Certain atmospheric factors and other sources of error can affect the accuracy of the GPS receiver. Garmin GPS receivers are usually accurate within 10 meters. Accuracy is even better on water. Some accuracy of the Garmin GPS receiver is enhanced by the WAAS (Wide Area Augmentation System).