About GPS and GPS Accuracy

The Global Positioning System is a network of 27 (24 in operation and three extras in case one fails) satellites in six different orbital paths. A GPS unit measures the speed of each satellite and compares it relative to your location. Once it has established contact, the device reads out the altitude, longitude and latitude. The unit keeps taking measurements and averages them constantly, which means that as time passes the device determines a more accurate position. A GPS device must acquire at least three satellites to determine a two-dimensional reading; four satellites are required for a 3D reading; and the accuracy grows as more satellites are acquired. GPS satellite signal are notoriously weak, and obstructions like dense tree cover and tunnels can impede the signals. GPS works anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.

Today's GPS receivers are extremely accurate, thanks to their parallel multi-channel design. 12 parallel channel receivers are quick to lock onto satellites when first turned on and they maintain strong locks, even in dense foliage or urban settings with tall buildings. Certain atmospheric factors and other sources of error can affect the accuracy of GPS receivers. Most GPS receivers are accurate to within 15 meters on average.

Newer GPS receivers with WAAS (Wide Area Augmentation System) capability can improve accuracy to less than three meters on average. No additional equipment or fees are required to take advantage of WAAS. Users can also get better accuracy with Differential GPS (DGPS), which corrects GPS signals to within an average of three to five meters. The U.S. Coast Guard operates the most common DGPS correction service. This system consists of a network of towers that receive GPS signals and transmit a corrected signal by beacon transmitters. In order to get the corrected signal, users must have a differential beacon receiver and beacon antenna in addition to their GPS.

Related Categories

• GPS Systems