2. Definition
 The Global Positioning System (GPS)
is a space-based satellite navigation
system that provides location and time
information in all weather, anywhere on
or near the Earth, where there is an
unobstructed line of sight to four or more
GPS satellites.

3. How does GPS works ?
 First the GPS satellites gives signal to
the moniter station than that signal will
be given to master station give names
to the places and areas than that master
station will finally give signal to the qausi
zenich satellites and finally the devices
will get information and signals.

5. Structure
 The current GPS consists of three major segments.
These are the space segment (SS), a control segment
(CS), and a user segment (US).] The U.S. Air Force
develops, maintains, and operates the space and control
segments. GPS satellites broadcast signals from space,
and each GPS receiver uses these signals to calculate its
three-dimensional location (latitude, longitude, and
altitude) and the current time.
 The space segment is composed of 24 to 32 satellites in
medium Earth orbit and also includes the payload
adapters to the boosters required to launch them into
orbit. The control segment is composed of a master
control station, an alternate master control station, and a
host of dedicated and shared ground antennas and
monitor stations.

6. Trilateration
 Imagine you are standing
somewhere on Earth with
three satellites in the sky
above you. If you know how
far away you are from satellite
A, then you know you must
be located somewhere on the
red circle. If you do the same
for satellites B and C, you can
work out your location by
seeing where the three circles
intersect. This is just what
your GPS receiver does,
although it uses overlapping
spheres rather than circles.
 The more satellites there are
above the horizon the more
accurately your GPS unit can
determine where you are.

7. GPS control Segments
 Master Control
Station
The master control station, located at
Schriever Air Force Base in Colorado
Springs, Colorado, is responsible for
overall management of the remote
monitoring and transmission sites.
GPS ephemeris being a tabulation of
computed positions, velocities and
derived right ascension and
declination of GPS satellites at specific
times, replace "position" with
"ephemeris" because the Master
Control Station computes not only
position but also velocity, right
ascension and declination parameters
for eventual upload to GPS satellites
 Monitor Station
Six monitor stations are located
at Schriever Air Force Base in
Colorado, Cape Canaveral,
Florida, Hawaii, Ascension
Island in the Atlantic Ocean,
Diego Garcia Atoll in the
Indian Ocean, and Kwajalein
Island in the South Pacific
Ocean. Each of the monitor
stations checks the exact
altitude, position, speed, and
overall health of the orbiting
satellites. The control
segment uses measurements
collected by the monitor
stations to predict the
behavior of each satellite's
orbit and clock.

8.  Ground antenaa
Ground antennas monitor and track the
satellites from horizon to horizon. They
also transmit correction information to
individual satellites.

10. Uses of GPS
 Military.
 Search and rescue.
 Disaster relief.
 Surveying.
 Marine, aeronautical and terrestrial navigation.
 Remote controlled vehicle and robot guidance.
 Satellite positioning and tracking.
 Shipping.
 Geographic Information Systems (GIS).
 Recreation.

11. Four Basic Functions of
GPS
 Position and coordinates.
 The distance and direction between any
two waypoints, or a position and a
waypoint.
 Travel progress reports.
 Accurate time measurement.