Global Positioning Systems (GPS) are changing the way in which people gather data for GIS. Forest companies use them to capture the boundaries of clear cuts, municipalities use them to gather locations of manholes, gutters, stop lights, etc., utility companies use them to locate poles, transformers, etc., remote sensing specialists use them in obtaining training sites and for quality control, and hikers use them to keep track of trails. GPS has 'democratized' data gathering in a way that no other technology has. Given how important GPS has become with respect to GIS, it is important that you have some understanding of how the 'global positioning system' operates, and what some of the potential problem areas can be.

There are many good pages on the net which describe Global Positioning Systems (GPS). Some of them provide fairly nontechnical introductions (such as the overview by Peter Dana at the University of Colorado Geographer's Craft), others provide more detailed technical discussions. A well organized list of links to many of the GPS sites around the world is maintained by the Geocommunity (GPS Links). Check out the How stuff works.com pages for an illustrated description of how a GPS receiver works. There are a number of sites listed in the Geocommunity site that provide non-technical overviews of GPS--check out the GPSy Resource Library, among others. A brief description (PDF) of the Russian GPS--GLOSNASS.

The BC Government specifications and guidelines for using GPS technology for resource mapping are available online. The US NOAA organization has a page which allows you to download for free GPS data for post-processing your GPS data. It should be useful for people working in the Vancouver area and the southern part of Vancouver Island. A discussion on why you can't use a GPS to generate an accurate DEM.

An ArcUser article describing the difference between GPS-based elevations and geodetic (the typical map-based) elevations. ESRI's ArcPad solution to linking GPS and GIS in a PDA. Some interesting web sites: satellite tracking, a list of GPS tracking sites. Winnipeg is the first city in the world to use GPS-based pay parking. A discussion of the European Galileo GPS project. The Chinese are also producing a system (called Beidou), the first system used a very different approach while the latest versions follow the approach described in class.

A project that may mean the end of GPS as we know it--Lightsquared: The interference issue. Interference solved? The GPS vendors' view.

Learning objectives

• Understand how GPS has fundamentally change spatial data collection;
• Recognize that precise GPS missions must be planned in advance (a prediction tool here);
• Understand important GPS terms such as WAAS, trilateration, DOP.

Text: GPS is mentioned in several places throughout the text, but nowhere in detail. Peter Dana's overview is probably the best 'outside' source for a general overview of GPS. Movies: 1, 2 [Overheads: 1 per page; 3 per page]

Keywords: trilateration, almanac (example), ephemeris, differential GPS (DGPS), DOP (PDOP, GDOP), LORAN, WAAS, Doppler effect (audio)