Global Positioning System 

WHAT IS GPS???A very precise positioning system

Developed and maintained by the US Department of Defense (DOD)

* 24 satellites* 20,200 km high orbit

Satellite based

Some facts about gps… Official name of GPS is Navigational Satellite

Timing And Ranging Global Positioning System (NAVSTAR GPS)

It costs about $750 million to manage and maintain the system per year

Mainly used for navigation, map-making and surveying

The GPS project was developed in 1973 to overcome the limitations of previous navigation systems

 It became fully operational in 1994. Roger L. Easton is generally credited as its inventor.

GPS consists of three major segments

1.Space segment

2.Control segment

3.User segment

1. SPACE SEGMENTA

constellation of 24

satellites

Kwajalein Atoll

US Space Command

Control Segment

Hawaii

Ascension Is.

Diego Garcia

Cape Canaveral

Ground AntennaMaster Control Station Monitor Station

3.User segment It consists of receivers that decode the signals from the

satellites.

The receiver performs following tasks:Selecting one or more

satellitesAcquiring GPS signalsMeasuring and trackingRecovering navigation data

Characteristics of gps Free Precise Reliable All weather Anytime and anywhere Unlimited user capacity

almost

How gps work… Uses measurements from 4+ satellites

Distance = travel time x speed of light

Determining gps position… The distance (x)

from one satellite tells us we're located somewhere on the surface of an imaginary sphere centered on that satellite with a radius of x.

x m

iles

Determining gps position… Distance

measurements from two satellites limits our location to the intersection of two spheres, which is a circle.

Determining gps position… A third

measurement narrows our location to just two points.

Determining gps position…

A fourth measurement determines which point is our true location

Signal structure Each satellite transmits its own

unique code Two frequencies used

L1 Carrier 1.57542 GHz L2 Carrier 1.22760 GHz

CodesCA Code use L1 (civilian code) P (Y) Code use L1 & L2 (military

code)

How accurate is gps??? Many factors can affect the accuracy

of GPS data. Accuracy can range from 1 centimeter to over 40 meters

significant parameter:-• Number of

visible satellites• Satellite

Geometry• Receiver Errors• Multipath

• Satellite Clock Errors• Time spent on measurement

• Atmospheric Effects• Operator knowledge and awareness

Multi path error

Satellite geometryPosition dilution of precision

Good PDOP Poor PDOP

Application of gps in automobiles In farmland Disaster

relief/emergency services

GPS Aircraft Tracking Robotics Missile and projectile

guidance Target tracking

Gps receivers

THANK YOU…….

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