Garmin GPS 12 MAP Owner's Manual

Also see for GPS 12 MAP: Declaration of conformity Supplementary guide Owner's manual & reference Specifications Quick guide

Garmin GPS 12 MAP Owner's Manual Manual pdf 13 page image

3The Global Positioning System (GPS) is asystem of 24 satellites which circle the earthtwice a day in a very precise orbit and transmitinformation to earth. The GPS 12 MAP mustcontinuously “see” at least three of thesesatellites to calculate your position and trackyour movement. At times, additional satellitesmay be needed to determine a position.By using an almanac (a timetable of satellitenumbers and their orbits) stored in the receiver’smemory, the GPS 12 MAP can determine thedistance and position of any GPS satellite and usethis information to compute your position.Your GPS receiver can only see satellites abovethe horizon, so it needs to know what satellites tolook for. To use this almanac data, your GPS needsto be told its general location (“initialized”) orgiven the opportunity to find itself.Initialization is necessary under these conditions:• The first time you use your receiver.• After the receiver has been moved over500 miles from the last time you used it.• If the receiver’s memory has been clearedand all internally stored data has been lost.Because the GPS 12 MAP relies on satellite signalsto provide you with navigation guidance, the GPSreceiver’s view of the sky will generally determinehow fast you get a position fix—or if you get a fix atall. GPS signals do not travel through rocks,buildings, people, metal, or heavy tree cover, so keepa clear view of the sky for best performance.Once the GPS 12 MAP has calculated a positionfix, you’ll have anywhere from five to twelvesatellites in view. The receiver will select thesatellites in view to update your position. If someof the satellites get blocked or “shaded,” thereceiver uses an alternate satellite to maintain theposition fix. A GPS receiver needs four satellites toprovide a three-dimensional (3D) fix, however, itcan maintain a two-dimensional (2D) fix withonly three satellites. A three-dimensional fixmeans the unit knows its latitude, longitude, andaltitude, a two-dimensional fix means the unitknows only its latitude and longitude.GETTING STARTEDWhat is GPS?When new (or if a posi-tion cannot be deter-mined after 5 minutes),the GPS 12 MAP willprompt you to initializethe receiver. The unitneeds a starting positionto determine which sat-ellites are in view.Check the Satellite Sta-tus Page for ‘2D Naviga-tion’ or ‘3D Navigation’to verify a position fix.