The
Global Positioning System (GPS)
Introduction
to GPS
The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.
Global
Positioning System (GPS) comprises of three parts:
- 24
satellites that orbit the Earth
- Ground
control stations which monitor the satellites
- GPS
receivers can be attached to persons or animals, or mounted on
an object, such as a vehicle
The
satellites are synchronised to emit encoded navigational information
(exact positioning and exact time). Any vehicle equipped with a
GPS receiver will intercept these transmissions. Using a simple
mathematical formula derived from triangulation, the receiver is
able to calculate its own longitude, latitude, velocity and even
altitude. For companies implementing GPS applications, this information,
most often, would be transmitted to a central dispatch or control
location.
Originally
designated the NAVSTAR (Navigation System with Timing And Ranging)
Global Positioning System, GPS was developed by the US Department
of Defense to provide all-weather round-the-clock navigation capabilities
for military ground, sea, and air forces.
Since
its implementation, GPS has also become an integral asset in numerous
civilian applications and industries around the globe, including
recreational uses (e.g. boating, aircraft, hiking), corporate vehicle
fleet tracking, and surveying. GPS employs 24 spacecraft in 20,200
km circular orbits inclined at 55 degrees.
These
spacecraft are placed in 6 orbit planes with four operational satellites
in each plane. All launches have been successful except for one
launch failure in 1981. The full 24-satellite constellation was
completed on March 9, 1994. GPS receivers use triangulation of the
GPS satellites' navigational signals to determine their location.
The
satellites provide two different signals that provide different
accuracies. Coarse-acquisition (C/A) code is intended for civilian
use, and is deliberately degraded. The accuracy using a typical
civilian GPS receiver with C/A code is typically about 100 metres.
The military's Precision (P) code is not corrupted, and provides
positional accuracy to within approximately 20 metres.
Numerous
on-line tutorials on how GPS works and it's applications are available,
including those at the University
of Colorado. GPS satellites are controlled at the GPS Master
Control Station (MCS) located at Falcon Air Force Base outside Colorado
Springs, Colorado. The ground segment also includes four active-tracking
ground antennas and five passive-tracking monitor stations.
Basic
Concept of GPS-based Applications
Fundamental
concept in GPS applications is that you can determine fairly accurately
(ordinarily within 10-30 metres) the location of any device that
has a GPS transceiver mounted inside the device. This determination
of this location is facilitated by a series of satellites maintained
by US defense establishment. Having determined the location of an
object one can track it's movement as it moves. Therefore, you can
implement a number of business and personal applications based on
this location like fleet management, health services in the public
sector and number delivery services.
How
it works
GPS
satellites circle the earth twice a day in a very precise orbit
and transmit signal information to earth. GPS receivers take this
information and use triangulation to calculate the user's exact
location.
Essentially,
the GPS receiver compares the time a signal was transmitted by a
satellite with the time it was received. The time difference tells
the GPS receiver how far away the satellite is. Now, with distance
measurements from a few more satellites, the receiver can determine
the user's position and display it on the unit's electronic map.
A
GPS receiver must be locked on to the signal of at least three satellites
to calculate a 2D position (latitude and longitude) and track movement.
With four or more satellites in view, the receiver can determine
the user's 3D position (latitude, longitude and altitude).
Once
the user's position has been determined, the GPS unit can calculate
other information, such as speed, bearing, track, trip distance,
distance to destination, sunrise and sunset time and more.
GPS
Applications
One
of the fast-growing GPS applications is vehicle tracking. GPS-equipped
fleet vehicles, public transportation systems, delivery trucks,
and courier services use receivers to monitor their locations at
all times.
Public
safety services, police, fire, and emergency medical services, are
using GPS receivers to determine the nearest service vehicle to
an emergency, enabling the quickest response in critical situations.
Recently,
automobile manufacturers are installing moving-map displays guided
by GPS receivers. For example, several Florida rental car companies
are demonstrating GPS-equipped vehicles that give directions to
drivers on display screens and through synthesised voice instructions.
Triangulation:
Collecting of signals from three or more satellites in carefully
monitored orbit from which the receiver computes it's own spatial
relationship to each satellite to determine it's position.
Automatic
Vehicle Location (AVL) is a technologically advanced method of remote
vehicle tracking and monitoring using GPS.
Each
vehicle is equipped with a module that receives signals from a series
of satellites, and calculates it's current geographical location,
speed, and heading. This information can be stored for later retrieval
or, frequently, transmitted to a central dispatch/control location
where it is displayed on a high-resolution geographical map.
For
additional information please click on the links below:
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