Global Positioning System -GPS by yyc62487


									George Ritchie
         Global Positioning System -
 Global. All-weather, 24hour, satellite based navigation system operated
  by the US Department of Defence for Military and Civilian use.
 24 GPS satellites in 12 hour orbits at a orbital height of 20,200 Km, held
  in 6 orbital planes.
              GPS – The Basics

 Triangulation is the basis
 To triangulate, the GPS receiver measures distance
  using radio signal travel times
 Accurate Time is achieved by solving unknowns
 Need to know where each satellite is in sky
 Finally correct for signal delays through space.
              Positioning Calculation

 Passive Ranging to the Satellites enables computation of User’s Position.
 Distance from User’s GPS Antenna to each Satellite calculated.
 4 satellites required as a minimum to calculate User’s Latitude,
  Longitude and height.
              Positioning Accuracy

   Positioning accuracy stand alone better than 25 metres,
    typically 5 to 15 metres.
 Accuracy depends on:
      GPS System Biases
      Number of Satellites in view
      Geometry of Satellites in view
      Receiver Quality
 Different Applications require different Accuracies.
                Differential Accuracy

 Accuracy can be improved down to 5mm by using a variety of
  Differential techniques.
 Corrections from both Coastal Beacons and Satellite can achieve sub-
  metre accuracy.
 Correction from 2nd High tech Receiver can achieve 5mm accuracy.
 Catch is the cost!
 Stand alone with No Differential - 5 to 15 metres – cost from £100
 Differential Sub-Metre – costs from £2000
 Differential 5mm – cost from £25000
 Need to Identify Accuracy Requirement.

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