Real-World Computing: GPS

The GPS system consists of a set of about 28 satellites that circle the earth and continuously broadcast an extremely accurate time signal. GPS receivers simultaneously receive the time signal from several satellites, and use the minute differences between the received times to accurately calculate the position of the receiver.

The simplest way to receive information from a GPS unit to a computer is to connect the GPS to the computer using a serial cable, and receive the NMEA data stream. The NMEA data stream consists of sequences of "sentences" containing information about current position, time, waypoints, and so on. With appropriate software, a computer can receive this information and display the current position on a moving map display, for example.

GPS manufacturers such as Garmin also have their own proprietary protocols for communicating with GPS and other navigational hardware.


The DNS database has the capability to hold the exact location of every named computer on the Internet. The DNS LOC site has lots of information about DNS LOC, including an application that draws the location of Internet hosts on a map.

Recreational GPS

There are some fun things you can do when you have precise worldwide location capability.

GeoCaching is like a worldwide "treasure hunt". People have hidden caches around the world, and have entered their coordinates on the site. With a handheld GPS, you can visit the listed locations to find what others have hidden.

The Degree Confluence Project is an effort to visit and take pictures at every whole-number latitude/longitude crossing point. No matter where you are on the planet, you are at most about 80 km away from the nearest confluence point.

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Greg Hewgill <>