GPS LOCATIONS FOR GIS: GETTING THEM RIGHT THE FIRST TIME

The Global Positioning System (GPS) is a very powerful tool which has, and will continue to provide the location data for attributes in many Geographical Information Systems (GIS). Manufacturers of GPS equipment have developed low cost, user-friendly receivers and software which are capable of easily satisfying many users' positioning requirements. Assuming the successful operation of GPS receivers and software, other measures are necessary to ensure the integrity of positions being entered into a GIS. This paper addresses one very essential consideration in using GPS for GIS: coordinate systems. As well, three positioning techniques suitable for many GIS are discussed and compared: single point positioning; differential positioning; and single point positioning with precise orbits and clocks. Results based on this last, recently introduced technique show that metre level accuracies may be achieved with a single receiver. Finally, a few suggestions are offered for novice users to help get GPS positioning right the first time.