In The Name Of God

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• In The Name Of God

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Global Positioning System

• By Moloud Heidary

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What I want to talk about?

• Definition of GPS.
• Determining position.
• Applications in military, navigation, surveying,
  .

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Definition

• 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
  scientific experiments.)

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( Global Positioning System ) ?? ????? ?????? ?
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Definition (cont)

• 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.

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NAVSTAR

• 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.

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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.

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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.
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Accuracy

• 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.

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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 spacecraft.

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Determining Position

• 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 spheres intersect.

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• 1- Satellite's position is determined relative to
  the Earth.
• 2- Location on Earth is located relative to the
  satellite.
• 3- THEN the Location's position on the Earth can
  be determined from the VECTOR sum of the other
  two measurements. All measurements must are done
  to such a precision that the location on the
  Earth is known to within 15 m.

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METHODS

• The distance from the satellite is determined by
  the time it takes for a radio wave to reach the
  site from the satellite.
• 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 imprecise.
• 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.

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Method(cont)

• 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 different
  satellites

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Receivers

• 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
  specified destinations.
• Some specialized GPS receivers can also store
  data for use in Geographic Information Systems
  (GIS) and map making.

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Receivers (cont)

• 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.

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GPS 315

• 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.

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Applications

• GPS has different uses such as
• Military
• Navigation
• Mobile satellite communication
• Location based services
• Surveying
• agriculture

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Military

• 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 coordinates.

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Navigation

• 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 vehicles.

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Mobile Satellite Communications

• 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.

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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.

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Location-based services

• 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
  US90 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.

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Surveying

• 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
  equipment.

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Agriculture

• 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.

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• Any question?

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Thank you !

• an essay by Larry Bogan ,December 18, 1998.
• http//www.gpsuser.pdf.
• http//www.erols.com/dlwilson/gpscomp.htm
• www. Wikipedia .com