Introduction To

G.P.S.

Contents

What is GPSThe need for positioning

systemSegments of GPS

• Space Segment• Control segment• Users Segment

How GPS WorksTRIANGULATIONApplications of GPS

What is GPS ??

GPS, which stands for Global Positioning System, is the only

system today able to show you your exact position on the Earth anytime,

in any weather, anywhere. Full name : NAVSTAR GPS

- NAVigation Satellite Time And Ranging

Global Positioning System

The need for positioning system

From the beginning of civilization, people wanted to know where they are or how to go to somewhere.

Ancient sailors used wind and stars to get the direction.

Also people have been using compass, map, and other methods to know their location and direction.

GPS can tell you where you are

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

Satellite Based 24 satellites 20,200 km high orbit

Six orbital planes with four satellites each

55° inclination with equator

Segments of GPS

1. Space SegmentA constellation of 24 satellites

2. Control segmentA network of earth-based facilities

3. Users Segment

SPACE SEGMENT

24 satellite vehicles

6 obital planes

Obital period of 11 hr 55

min

20,200 km elevation above

Earth

Five to eight satellites

visible from any point on

Earth

CONTROL SEGMENT

Monitor and control GPS satellites

One master control station (MCS)

Five monitor stations

Three ground antennas

GPS Monitoring Station

User Segment

• Receive signal from satellites • calculate current position and speed/direction

How GPS Works ………

Uses measurements from 4+ satellitesDistance = travel time x speed of light

Time Difference

•The GPS receiver compares the time a signal was transmitted by a satellite with the time it was received.• The time difference tells the GPS receiver how far away the satellite is.

Calculating Distance

Velocity x Time = Distance

Radio waves travel at the speed of light, roughly 186,000 miles per second (mps)

If it took 0.06 seconds to receive a signal transmitted by a satellite floating directly overhead, use this formula to find your distance from the satellite.

186,000 mps x 0.06 seconds = 11,160 miles

TRIANGULATION• Suppose Satellite A to our

position is 11,000 miles• At this point we could be located

anywhere on the specified sphere

• Next, let us take another measurement from a second satellite, Satellite B

• Now our position is narrowed down to the intersection of theses two sphere

Satellite A+

Satellite B+

Satellite C+

Determining GPS Position

Satellite A

Satellite B+

+

• Taking another measurement from a 3rd satellite narrows our position down even further, to the two points

• These points are located where the 3rd sphere cuts through the intersection of first two spheres

• So by ranging from 3 satellites we can narrow our position to just two points in space

• We could make a 4th measurement from another satellite to determine the true point

• Or, We can eliminate one of the two points that gives a point which may be

too far from the earth• However, GPS receivers use a 4th satellite

to precisely locate our position

GPS for Navigation

Military Applications

• Digital Assistant for soldiers

(personal navigation)

• Search and rescue missions• Detect nuclear detonation with

sensors on satellites(optical sensor, X-ray sensor, EMP sensor, etc..)

Applications of GPS

Civilian Applications

• Vehicle navigation (for cars, airplanes, and ships)

- Use GPS to determine position, speed, and direction

Civilian Applications• Used in map-making and land

surveying

• Various usages in many fields of

industry

• Outdoor Activities (Hike/bike

trails, GeoCaching)

Civilian Applications• Location-based service (LBS), Social Network Service (SNS)

- Finding the location of family or friend- Integrate current location with social network- Using GPS-enabled phones (mostly smart phones)

• http://www.howstuffworks.com/gps.htm

•http://www.howstuffworks.com/38-how-gps-works-video.htm

• http://en.wikipedia.org/

References

Questions…???