2 Global Positioning System -GPS 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.
3 GPS – The Basics Triangulation is the basis To triangulate, the GPS receiver measures distance using radio signal travel timesAccurate Time is achieved by solving unknownsNeed to know where each satellite is in skyFinally correct for signal delays through space.
4 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.
5 Positioning AccuracyPositioning accuracy stand alone better than 25 metres, typically 5 to 15 metres.Accuracy depends on:GPS System BiasesNumber of Satellites in viewGeometry of Satellites in viewReceiver QualityDifferent Applications require different Accuracies.
6 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 £100Differential Sub-Metre – costs from £2000Differential 5mm – cost from £25000Need to Identify Accuracy Requirement.