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Definition of GPS.
Applications in military, navigation,
The Global Positioning System, usually
called GPS, is the only fully-functional
satellite navigation system(allow small
electronic devices to determine their
location (Longitude, Latitude, and Altitude)
in within a few meters using time signals
transmitted along a line of sight by radio
from satellites. Receivers on the ground
with a fixed position can also be used to
calculate the precise time as a reference for
GPS has become a vital global utility,
indispensable for modern navigation on land,
sea, and air around the world, as well as an
important tool for map-making and land
surveying. GPS also provides an extremely
precise time reference, required for
telecommunications and some scientific
research, including the study of earthquakes.
GPS receivers can also gauge altitude and
speed with a very high degree of accuracy.
The United States Department of
Defense developed the system, officially
named NAVSTAR GPS (Navigation
Signal Timing and Ranging Global
Positioning System), and launched the
first experimental satellite in 1978.
GPS as public good:
Although the cost of maintaining the
system is approximately 400 million$
per year, including the replacement
of aging satellites, GPS is available
for free use in civilian applications as
a public good. In late 2005, the first in
a series of next-generation GPS
satellites was added to the
constellation, offering several new
capabilities, including a second
civilian GPS signal called L2C for
enhanced accuracy and reliability.
This taxi in Kyoto equipped with
GPS navigation, is an example
of how GPS technology can be
applied in routine activities.
This is a great little GPS
receiver that lets you know
where you are, and where you
need to go. It's Bluetooth so you
can use it in your pocket, with
your iPAQ or laptop, and with
whichever software your
choose. your love this device.
The GPS (Global Positioning System) is a
"constellation" of at least 24 well-spaced satellites that
orbit the Earth and make it possible for people with
ground receivers to pinpointtheir geographic location.
The location accuracy is anywhere from 1 to 100
meters depending on the type of equipment used . In
coming years it reduce into 1cm with DGPS(. The
DGPS eliminates selective availability (SA) and
provides a much more accurate determination of
time and position). The GPS is owned and operated
by the U.S. Department of Defense, but is available for
general use around the world.
How does it work:
GPS works like this:
A minimum of 24 GPS satellites are in orbit at 20,200
kilometers (12,600 miles) above the Earth. The
satellites are spaced so that from any point on Earth, at
least four satellites will be above the horizon.
Each satellite contains a simple computer, atomic
clocks, and various radios. With an understanding of its
own orbit and the clock, the satellite continually
broadcasts its changing position and time. The
satellites use their on-board atomic clocks to keep
precise time, but are otherwise very simple and
unsophisticated when compared to other modern
A GPS receiver "knows" the
location of the satellites. By
estimating how far away a
satellite is, the receiver also
"knows" it is located
somewhere on the surface
of an imaginary sphere
centered at the satellite. It
then determines the sizes of
several spheres, one for
each satellite. The receiver
is located where these
• 1- Satellite's position is
determined relative to
• 2- Location on Earth is
located relative to the
• 3- THEN the Location's
position on the Earth
can be determined from
the VECTOR sum of
the other two
are done to such a
precision that the
location on the Earth is
known to within 15 m.
The distance from the satellite is determined by the
time it takes for a radio wave to reach the site from
distance = (speed of light) x (time of flight)
This is very simple but there are a few difficulties:
The receiver clock is not exactly synchronized with
the satellite clock so the time of flight will be
The satellite and receiver are in different velocity
reference frames and gravitational regimes .
The speed of light is 300,000 km/s in a vacuum.
However, while traveling through the Earth
Ionosphere and Troposphere, the radio waves
travel at slightly slower speeds.
The location is a vector and
must also include direction. In
order to do this, distances
from several satellites are
required. This is called
triangulation. We wish to find
our latitude, longitude and
height above the center of the
Earth. These are three
different numbers and would
require distances to three
If the receiver is also equipped with a display
screen that shows a map, the position can be
shown on the map.
If a fourth satellite can be received, the
receiver/computer can figure out the altitude as
well as the geographic position.
If you are moving, your receiver may also be
able to calculate your speed and direction of
travel and give you estimated times of arrival to
Some specialized GPS receivers can also
store data for use in Geographic Information
Systems (GIS) and map making.
Many different types of receivers have become
less and less expensive in recent years. They are
now portable enough to put in your pocket.
Internal active antenna are sensitive enough to
pick up 8 satellites even under tree cover. An
external antenna is still better and more flexible.
• Affordable and easy to use, the GPS
315 is the ultimate outdoor guide.
Nine easy-to-follow graphic
navigation screens show bearing,
heading, distance, speed and more
on a high-resolution.
GPS has different uses such as:
Mobile satellite communication
Location based services
GPS allows accurate targeting of various
military weapons including cruise
missiles and precision-guided munitions,
as well as improved command and
control of forces through improved
locational awareness. The satellites also
carry nuclear detonation detectors,
which form a major portion of the United
States Nuclear Detonation Detection
System. Civilian GPS receivers are
required to have limits on the velocities
and altitudes at which they will report
GPS is used by people around the world as a
navigation aid in cars, airplanes, and ships.
Personal Navigation Devices(PND) such as
hand-held GPS are used by mountain
climbers and hikers. Glider pilots use the
logged signal to verify their arrival at turn
points in competitions. Low cost GPS
receivers are often combined with PDAs, cell
phones, car computers, or vehicle tracking
systems.. The system can be used to
automate harvesters, mine trucks, and other
Satellite communications systems permit
"remotes” to communicate with "hubs"
via satellites. A typical system uses
satellites in geosynchronous orbit: this
requires a directional antenna (usually a
"dish") that is pointed at the satellite.
When the "remote" is portable, as on a
ship or a train, the antenna must be
pointed based on its current location.
Essentially all modern antenna
controllers incorporat a GPS receiver to
provide this location information.
Location-based services :
GPS functionality can be used by
emergency services and location-based
services to locate mobile phones.
Assisted GPS is a GPS technology often
used by the mobile phone because it
reduces the power requirements of the
mobile phone and increases the
accuracy of the location obtained.
GPS receivers come in a variety of formats,
from devices integrated into cars, phones,
and watches, to dedicated devices .The
availability of hand-held GPS receivers for a
cost of about US$90 and up has led to
recreational applications including location-
based games like the popular game
Geocaching. Geocaching involves using a
hand-held GPS unit to travel to a specific
longitude and latitude to search for objects
hidden by other geocachers.
More costly and precise receivers are used
by land surveyors to locate boundaries,
structures, and survey markers, and for
road construction. There is also a growing
demand for Machine Guidance such as
Automatic Grade Control systems that use
GPS positions plans to automatically control
the blades and buckets of construction
GPS Machine Guidance is used for
tractors and other large agricultural
machines via auto steer or a visual aid
displayed on a screen, which is
extremely useful for controlled traffic
and row crop operations and when
spraying. As well as guidance, GPS
used in harvesters with yield monitors
can provide a yield map of the
paddock being harvested.