The Global Positioning System (GPS) is managed by the U.S. Air Force and became fully operational in 1993. It uses 24 satellites that orbit 11,000 miles above Earth and constantly broadcast signals. A GPS receiver needs signals from at least 4 satellites to determine its 3D position and time offset. The system has three segments - space (satellites), control (ground stations), and user (receivers). Receivers use trilateration of distance measurements to satellites to calculate their latitude, longitude, or UTM coordinates. Accuracy can be affected by satellite geometry, orbits, multipath signals, and atmospheric conditions.

1. GLOBAL POSITIONING SYSTEM
PRESENTED BY
D.KAVIYA
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The current system is managed by the U.S Air
Force for the Department of Defense (DOD).
The current system became fully
operational June 26, 1993 when the 24th
satellite was lunched.
A minimum of four GPS satellite signals are
required to compute positions in three
dimensions and the time offset in the
receiver clock.
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4. 
Space segment

Control segment

User segment
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The GPS uses a constellation of 24 satellites that
orbit the earth at about 11,000 nautical miles,
once every 12 hours.
The orbital position is constantly monitored and
updated by the ground stations.
Each satellite is identified by number and
broadcasts a unique signal.
Space Segment--Satellite Signals
•The GPS system uses two types of signals to calculate distance.
Code-phase ranging
Carrier-phase ranging
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The receiver collects, decodes and processes the
satellite signals.
The basic receiver does not include a transmitter.
Different levels of precision are available.
The receiver determines its location by trilateration.
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Knowing its distance from
three satellites, the
receiver can determine
its location because there
is only two possible
combinations and one of
them is out in space.
In this example, the
receiver is located at b.
The more satellite that
are used, the greater the
potential accuracy of the
position location.
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8. Once the GPS receiver has located its position it is
usually displayed in one of two common formats:
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Latitude and longitude
Universal transverse Mercator (UTM).
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9. Latitudes
and
longitudes
are angles.
Both use the center of the earth as the vertex, but they use a different zero
reference.
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10. The world is divided into 60
zones of latitude, each 6o wide
at the equator, that extend from
84o N to 80o s.
These zones begin at 180o longitude and
are numbered consecutively eastward.
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11. Each system has its advantages and disadvantages.
UTM
Latitude and longitude
Advantages
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With the proper
instruments, a person can
determine their position at
the site without using GPS.
Used by most maps
Disadvantages
Difficult to determine
distances between two or
more points.
Advantages
Best method for determining
distances between two points.
Disadvantages
Not as useful for finding a
location.
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12. The ground segment has one master control, one alternative master control
station, 12 command and control antennas and 16 monitoring sites.
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13. 
Satellite geometry
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Satellite orbits
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Multipath
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Atmospheric effects
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14. Though
it has some limitation, it does not
considered as a big error
Because these errors are only nano errors
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