Posted to GPS Articles 2008-10-28
The Global Positioning System (GPS) is a Global Navigation Satellite System (GNSS) which was launched in 1973 by the United States Department of Defense. Currently it is the only functioning GNS system in the world. GPS was originally intended for military applications, but in the 1980s, the US government made the system available for civilian use. The Global Navigation Satellite System has at any time 24 to 32 satellites; which orbit the earth, at an approximate altitude of 12,600 miles.
At least six satellites are within line of site from almost anywhere on the surface of the earth. Generally, GPS works in any weather conditions, anywhere in the world, 24 hours a day and has no subscription fees or setup charges to use. Its official name is NAVSTAR-GPS and you may see this name used by manufacturers in the instruction books for there GPS navigational devices such as the Garmin nuvi 275T.
Each GPS satellite continuously broadcasts a Navigational Message. The GPS device, the consumer is using encodes information to identify its location. In addition, manufactured devices can now overlay maps, streets, even retail outlets for the user to more effectively travel.
So how does it work?
A GPS satellite circles the earth twice a day in a predetermined orbit and transmits information to earth. GPS receivers gather this information and uses triangulation to calculate the user's exact location. In other words, the GPS receiver is telling you where you are, with an extremely accurate calculation, and displays the user's position on the unit's electronic map.
A GPS unit has to be locked on to the signal from a minimum of three satellites to calculate a 2D (2 dimensional) position (longitude and latitude) and track movement. With four to six satellites in view at any given time, the receiver will determine the user's 3D location (longitude, latitude and altitude). Once the user's position has been located, the GPS device can calculate other information, such as bearing, track, speed, distance, destination, sunrise and sunset plus more.
Today there are many GPS devices manufactured to use this satellite system including auto GPS, Handheld GPS, Cell phones and car location systems to name a few.
