GPS is a satellite-based navigation system that provides precise geographic positioning anywhere in the world. It uses a constellation of 24 satellites in medium Earth orbit that transmit signals allowing GPS receivers to determine their latitude, longitude, and elevation. The system is maintained by the US Department of Defense and provides free and accurate positioning to unlimited civilian users globally. GPS works by precisely measuring the time it takes signals from four or more satellites to reach a GPS receiver, allowing the device to calculate the user's position by triangulating the distances to the satellites. With factors like receiver quality, satellite geometry, and signal processing, positions can be accurate to within a few meters for most applications.

1. GLOBAL POSITIONING SYSTEM
Prepared By : Patel Jay C
ME(EC)-140870705004
An easy to use
technology for everyone

2. What is GPS ?
A very precise positioning system
• Developed and maintained by the US Department of Defense
(DOD)
• Satellite Based
* 24 satellites
* 20,200 km high orbit

3. BUT!
Although it is a very precise geographic positioning system
•It is very easy to get yourself into trouble
•Why?
•Because you (probably) don’t understand how it works
•And that leads to garbage
•Now First We learn the prerequisite terms

4. Latitude
What is Latitude?
• Lines of Latitude run horizontally
• Latitude is measured in degrees.
• The Equator is 0 degrees Latitude.
• Lines of Latitude locate places North or South of the Equator.
• The North Pole is 90 degrees N Latitude, and the South Pole is 90 degrees
S Latitude.

5. Longitude
• Lines of Longitude run vertically.
• They are also called Meridians.
• The Prime Meridian is found in Greenwich, England.
• The Prime Meridian is 0 degrees Longitude.
• Lines of Longitude locate places East or West of the Prime Meridian.
• There are 180 degrees of east Longitude, and 180 degrees of west Longitude.

6. Characteristics of GPS
• Free
• Precise
• Reliable
• Anytime & anywhere
• All weather
• Unlimited user capacity
Almost!

7. Segments of GPS
1. Space Segment
A constellation of 24 satellites
2. Monitor Station
A network of earth-based facilities
3. Users & Equipment
Source:Trimble

8. Segments of GPS
1. Space Segment
A constellation
of 24 satellites

9. GPS Monitoring Station

10. How GPS Works ………
Uses measurements from 4+ satellites
Distance = travel time x speed of light
Source:Trimble

11. Determining GPS Position
• Suppose the distance from
Satellite A to our position is 11,000
miles
• At this point we could be located
anywhere on the specified sphere
Satellite A
+
• Next, let us take another measurement
from a second satellite, Satellite BSatellite B
+
• Now our position is narrowed down to the
intersection of theses two sphere

12. 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
• So by ranging from 3 satellites we can narrow our
position to just two points in space
• These points are located where the 3rd
sphere cuts through the the intersection of
first two spheres

13. Satellite C
+
How do we decide which one is our true
location?
Satellite A
Satellite B
+
+
• We could make a 4th measurement
from another satellite to determine
the true point
• However, GPS receivers use a 4th satellite to precisely
locate our position
• We can eliminate one of the two
points that gives a ridiculous
answer
• The ridiculous point may be too far
from the earth
OR

14. Determining GPS Position

15. How accurate is GPS?
Depends on some variables
• Design of receiver
• Relative positions of satellites, technically known as PDOP (Position
dilution of precision)
• Postprocessing
• Time spent on measurement

16. GPS Receivers

17. GeoXT Versus Garmin
Mostly used for GIS data collection
Mostly used for
recreational purposes

18. How accurate is GPS?
Depends on some variables
• Design of receiver
• Relative positions of satellites, often known as DOP (Dilution of
Precision)
• Postprocessing
• Time spent on measurement

19. WAAS
• Wide Area Augmentation System.
• It provides FREE GPS differential correction data for visible satellites.
• Developed & operated by the FAA (Federal Aviation Administration) for flight
navigation but it’s available free to GPS users.
• WAAS-enabled receivers can provide sub-meter level accuracy anywhere in
most locations of the US and southern Canada.

20. WAAS
• Differential corrections are computed from ground stations and then
uploaded to geostationary satellites for broadcasting.
• WAAS-enabled GPS receiver automatically uses such correction data to
enhance the positional accuracy.

21. PDOP
Multipath
SNR
Sources of error
Source:Trimble

22. Multipath
• When GPS signals arrive at the receiver
having traveled different paths

23. What is a PDOP?
• Position Dilution of Precision
Good PDOP Poor PDOP

24. SNR (signal-to-noise ratio)
• SNR determines the signal strength relative to noise
• GPS position is degraded if the SNR of one or more satellites
in the constellation falls below certain range
Signal Strength
Indicators

25. Common use of GPS
A. GIS data collection & mapping
B. Navigation
C. Recreation

26. GPS for Navigation

27. GPS for Navigation
• GPS in PDA
are getting popular in car
comes with voice guidance.

28. GPS in Recreation

29. GPS in Farmland

30. Future GPS
A. GPS in USA
B. GLONASS program from Russia
C. GALILEO from European countries