An Introduction to GPS and DGPS
| An Introduction to GPS and DGPS |
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The Global Positioning System (GPS) is made up about 24 satellites orbiting about 11,000 miles up which are constantly broadcasting a clock signal. GPS receivers on the ground pick up several of these signals and measure the different times that are received. Knowing those times, you can calculate where you are on the planet accurate to within a few meters. With the addition of ground based DGPS signals that accuracy improves to a few inches.
The basis of GPS is triangulation. By knowing the position of three satellites in space and your distance to each of them, you can calculate how far away from each you are, and thus your exact position on the planet or in the air. The more satellite signals you get the more accurate the calculation is. Trimble has an excellent introduction to GPS which I highly recommend reading for more information. For the GPS receiver to interface to the computer, it sends out the data in various formats. Each format is different but there is usually a standard NMEA format available. NMEA is a text stream with comma separated data such as |