What is GPS
The 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 installation fees.
How GPS Works
GPS satellites circle the earth twice a day in a precise orbit. Each satellite transmits a unique signal and orbital parameters that allow GPS units to decode and calculate the exact location of the satellite. GPS receivers use this information and trilateration to calculate a user's exact location. Essentially, the GPS receiver measures the distance to each satellite by the time it takes to receive a transmitted signal. With distance measurements from a few satellites, the receiver can determine a user's position and display it.
To calculate your 2-D position (latitude and longitude) and track motion, a GPS receiver must be locked on at least 3 satellites. With 4 or more satellites in sight, the receiver can determine your 3-D position (latitude, longitude and height). Generally, a GPS receiver will track 8 or more satellites, but it depends on time of day and where you are on Earth. Once your position has been determined, the GPS unit can calculate other information, such as
- Trip dist
- Distance to Target
What is signal
GPS satellites transmit at least 2 low-power signals. The signals move through the field of view, which means that they will pass through clouds, glass and plastic, but will not go through most of the fixed objects such as buildings and mountains. However, modern receivers are more sensitive and can usually trace through houses. A GPS signal contains 3 different types of information
It is an I.D. code that identifies which satellite transmits information. You can see which satellites you receive signals from on the unit's satellite side.
Ephemeris data is needed to determine a satellite's position and provides important information on the health of a satellite, current date and time.
Almanac data tells the GPS receiver where each GPS satellite should be any throughout the day and displays the orbital information of that satellite and all other satellites in the system.