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.
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[BROKEN]);
- Understand important GPS terms such as WAAS, trilateration, DOP.
Required Readings
Pocket GPS World: How does the Global Positioning System work?
Overheads: Lecture 12: Global Positioning Systems
Recommended Readings
There are many good pages on the net which describe Global Positioning Systems (GPS). Some of them provide fairly nontechnical introductions others provide more detailed technical discussions. Here is a link to a magazine that covers recent advances in GPS and other related technologies: GPS World Magazine
Video Clips
Useful Resources
NOAA: Continuously Operating Reference Station (CORS) and, related, from Garmin: What is WAAS?
Can You Use GPS Data to Make a DEM? - A discussion on why you can’t use a GPS to generate an accurate DEM
ESRI: Mean Sea Level, GPS, and the Geoid - an ArcUser article describing the difference between GPS-based elevations and geodetic (the typical map-based) elevations
Winnipeg Free Press: Plug the meter? Forget about it - Winnipeg was the first city in the world to use GPS-based paid parking
N2YO.com - satellite tracking website
GLONASS: The Russian GPS compared to the US system
European Space Agency (ESA): What is Galileo?
Wikipedia: BeiDou Navigation Satellite System - The Chinese are also producing a system (called Beidou).
The Financial Express: US cops get Bond-style Global Positioning System bullet to track cars -
How Stuff Works: 2-D Trilateration
About Tech: GPS Almanac
DOP, the non-technical description
Wikipedia: Loran
Wake Forrest University: Doppler Effect Video/Audio Clips
Keywords
trilateration, almanac, ephemeris, differential GPS (DGPS), DOP (PDOP, GDOP), LORAN, WAAS, Doppler effect (audio)