1. George Ritchie

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 times
Accurate Time is achieved by solving unknowns
Need to know where each satellite is in sky
Finally 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 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.

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 £100
Differential Sub-Metre – costs from £2000
Differential 5mm – cost from £25000
Need to Identify Accuracy Requirement.