Global Positioning
    System
 The System
 The Position Solution
 Hardware
 Ionospheric And
    Atmospheric Delays
 The Signals
 Dynamic Positioning
 Static Positioning
 Coordinate Systems
 Conclusions

Global Positioning System

Introduction

The topic of GPS will be dealt with in this subject at a very introductory level. These reference notes are designed to accompany a course in plane surveying, whereas GPS positioning takes place on a complex surface which can be only approximately modelled by a spheroid. In order to understand fully the solution to GPS positioning a high level of geodetic and mathematical knowledge is required. This will be provided in the later years of the Geomatic courses.

The Navigation Satellite Timing and Ranging (NAVISTAR) Global Positioning System (GPS) is a network of orbiting satellites that can be used to provide information on the location of a signal receiver on the earth's surface. The system has the potential to revolutionise the practice of surveying and navigation, and investigations and applications to date give some truth to this prediction.

In it's simplest form, a signal receiver on the surface of the Earth (say mounted on a surveyor's tripod, on a boat, or in an aircraft) receives signals from the satellites. Clocks within the signal receiver measure the time the signal has taken to travel from the satellite to the receiver's position on the Earths' surface. As the rate at which the signal is travelling is known, the distance from the satellite to the receiver can be determined. If the distance of the receiver's position can be measured in relation to four different satellites, then the three dimensional location of the receiver can be determined with respect to these satellites. If the positions of the satellites is known then absolute location can be derived. This can be performed in a matter of minutes in a hand-held receiver for less than $1000AUD, or to around centimetre precision using more sophisticated, more expensive, instruments.

The availability of the system now means that anybody can determine a unique location on the surface of the planet or navigate across it, not just those lucky few learned in the black arts of astronomy and geodetic positioning (that is, Geomatics professionals). Yacht owners, bush walkers, 4 wheel drivers, BMW Series 7 owners, ambulances, CFA fire tenders, pilots, explorers, inhuman Serbian snipers, Polaris missiles, the French Marines, Greenpeace and techno-junkies all now have access to positioning information previously unavailable.