Traqmate User Manual V1.0
June 14, 2005
Copyright © 2005 Track Systems Technologies, LLC
Page 44
GPS Frequently Asked Questions
What is GPS?
The Global Positioning System is a constellation of 24 satellites that orbit the earth twice a day,
transmitting precise time and position (latitude, longitude and altitude) information. With a GPS
receiver, users can determine their location anywhere on the Earth. The complete system
consists of 24 satellites orbiting about 12,000 miles above the Earth, and five ground stations to
monitor and manage the satellite constellation. These satellites provide 24-hour-a-day coverage
for both two-and three- dimensional positioning anywhere on Earth.
Development of the $10 billion GPS satellite navigation system was begun in the 1970s by the
US Department of Defense, which continues to manage the system, to provide continuous,
worldwide positioning and navigation data to US military forces around the globe. However, GPS
has an even broader civilian, commercial application. To meet these needs, GPS offers two
levels of service, one for civilian access and the second encrypted for exclusive military use. The
GPS signals are available to an unlimited number of users simultaneously, and there is no charge
for using the GPS Satellites.
How Does GPS Work?
The basis of GPS technology is precise time and position information. Using atomic clocks and
location data, each satellite continuously broadcasts the time and its position. A GPS receiver
receives these signals, listening to three or more satellites at once, to determine the users
position on earth.
How Accurate is GPS?
Traqmate is equipped with a form of differential GPS known as WAAS. A WAAS-capable receiver
can give you a position accuracy of better than three meters (10 feet) in absolute terms over a
large span of time. In product testing on racetracks, which typically have a good view of the sky,
recordings done close together in time were shown to be repeatable to one meter
accuracy
.
Under normal conditions, the GPS signal will provide a civilian user an accuracy of better than 15
meters (50 feet). However, using a technique called differential GPS (DGPS), the user can
increase the overall accuracy of the GPS receiver to approximately 1-3 meters. With DGPS, one
GPS receiver unit is placed in a known location and the position information from that receiver is
used to calculate correction in the position data transmitted to other GPS receivers in the area.
The resulting real-time accuracy is in the 10 foot range. Sub-meter accuracy can be obtained by
using DGPS and post-processing calculations in static positioning.
WAAS stands for Wide Area Augmentation System, which is a system of satellites and ground
stations that provide GPS signal corrections, giving you even better position accuracy. A WAAS-
capable receiver can give you a position accuracy of better than three meters, 95 percent of the
time. Currently, WAAS satellite coverage is only available in North America.
