What is it?
The Global Positioning System (GPS) is a navigation and positioning system which relies on a network of satellites orbiting the earth. These satellites were launched by the US Department of Defense for military use, but in the 1980s, the government made GPS freely available for civilian use as well.
How it works?
Each GPS satellite has an on-board atomic clock and continually transmits signals to earth containing the current time. Based on the time that it receives these signals, a GPS receiver can calculate the distance to each satellite and use this information to triangulate the receiver's exact location. A GPS receiver must be locked on to at least three satellites to calculate its latitude and longitude, and must be locked on to at least four satellites to calculate its altitude. By keeping track of positions and times, a GPS receiver can calculate other information such as speed, direction, and distance travelled. GPS receivers commonly use the NMEA protocol to transfer data to a computer.
Many factors can affect the accuracy of GPS readings, including atmospheric effects, radio signal reflections, clock errors, and even relativity. Most GPS receivers on the market claim to be accurate to within 3 to 15 meters (10 to 50 feet).
Types of GPS Trackers
Data Loggers
- A GPS logger records position information at regular intervals and stores the data to internal memory. A user can then download the data onto a computer for further analysis.
Data Pusher
- This type of device sends out information about its position at regular intervals. A server receives this data and analyzes it. These devices can be used to track vehicles or even wildlife.
Data Pullers
- These devices are similar to data pushers, except that, instead of broadcasting the signal at regular intervals, the device can be queried for it's data. An example of this is our very own gpsd.
Interesting Facts
- GPS satellites travel at about 7,000 miles per hour.
- GPS satellites are only built to last 10 years.
- Transmitter power is only 50 watts or less.
- US manufacturers cannot export GPS receivers that work above 60,000 feet traveling at over 1,000 knots.
