What is Global Positioning System (GPS)?

Posted by on 10/20 at 09:51 AM Permalink

The Global Positioning System, commonly known as GPS, is a network of satellites that determines a ground based user’s specific latitude, longitude, and altitude. GPS devices have become more integrated in our daily lives through navigation computers in cars to emergency locators in cellular phones. GPS can even keep the time accurate on watches and VCRs. Portable GPS receivers are becoming increasingly popular for young and old alike.

Read Full Article Here:
http://www.geeks.com/techtips/2006/portable-gps-receivers.htm

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    Posted by Ted Tatro  on  10/22  at  05:54 PM

  1. I recently purchased a GPS for a watercraft, it is a Lowrance-350A. On the left side top to bottom there are 7 buttons, sens, range, zoom, auto, waypt, waypt-quick save, and menu. On the right side it has a button program much like you would see on a dvd player handheld control, except at the bottom of the controls there are 2 buttons, left, event marker, and right, man overboard. Along the bottom the buttons are sonar, GPS, Plotter, Windows and off and on. Can you tell me if this can be used in an automobile and an approximation of its value? THX, TJT.

    2. Posted by Jon  on  10/22  at  06:28 PM

  2. Accuracy is very high now.  see artical below
    http://www.ngs.noaa.gov/FGCS/info/sans_SA/docs/statement.html

    3. Posted by Bill Schober  on  10/22  at  09:03 PM

  3. A correction to your TechTip: President Bill Clinton signed an order, over 6 years ago, that made non-gov GIS far more accurate that 100 meters!  My GPS units, with WAAS enabled, are accurate to less than a couple feet!!!  Check your facts a little better.  Also GPS watches not only keep better time, but hey also give your current Lat. and Long.

    4. Posted by Finn Lassen  on  10/23  at  06:47 AM

  4. There are several inaccuracies in the article.
    “...satellites that determines...”. The satellites themselves don’t determine anything. They continuously broadcast their data. Their broadcasted signals are used by the GPS receiver to determine the receiver’s location.
    The comparison to RADAR is inapt. If you want to talk about GPS’s predecessors you could mention LORAN, VOR/VORTAC and ADF. All based on fixed groundbased stations that continuously broadcast their signals in all directions. Those signals are used by the applicable receivers in aircrafts, boats or other vehicles to determine position. RADAR is different in that the groundbased station transmits a signal and receives the signal back after it has bounced off the target you’re trying to locate. The target does not know its location unless told by the RADAR station by two-way radio.

    I don’t believe that the current GPS system uses the doppler effect.

    As far as I know, the “de-tuning” (selective availability) was suspended several years ago and accuracy is now down to 15 meter or better.

    Calling an emergency locator beacon with built-in GPS a “GPS transponder” is a misnormer, as least for aircraft emergency locator beacons automatically activacted on impact. May be true for LowJack systems.

    Are you aware of any cellphones being produced today that does not have a GPS receiver built-in (whether hidden or not)? I thought that was mandated by law since 2005.

    5. Posted by Ernie  on  10/23  at  04:13 PM

  5. Article has major flaws.

    1. Selective Availability was turned off in 2000, current accuracy of the signal is approximately 10meters.

    2. Majority of Airliners do not have GPS, they use Inertial Nav.

    3. Majority of General Aviation aircraft that fly in the Air Traffic Control System have Certified GPS systems.

    6. Posted by Michael  on  10/25  at  07:34 AM

  6. As many have mentioned, the correct accuracy for civilian GPS is less than 10 meters. The sentence originally said ‘to approximately 10 meters’ instead of 100. This was a revision typo at publication time and is being corrected. I realize that many GPS receivers can go beyond this limit too. Not all airliners use GPS as older aircraft have not converted, but GPS is available for use in both public and private aircraft.

    I am glad to see that people are reading the Tech Tips and feel passionately to help correct mistakes. Thanks for reading.

    7. Posted by John Nakata  on  10/30  at  05:11 PM

  7. If your GPS receiver had a clock with absolute accuracy of a few nanoseconds of UTC, then your receiver can triangulate from just 3 satellites.  Just 1 microsecond error can be about 1000 ft.  However, a forth satellite can resolve the problem of not having a super accurate clock in your receiver.  So, most consumer receivers need to receiver at least 4 satellites.

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