Transcript No Slide Title

Overview
• Introduction
• The
GPS System (3 components)
• Calculating a Position
• Differential GPS
Introduction
Introduction
NAVSTAR GPS:
• Navigation Satellite Timing and Ranging Global
Positioning System
• Funded and controlled by the US Department of
Defence
COMPOSED OF THREE MAIN SEGMENTS
• Space Segment
• Control Segment
• User Segment
Components
SPACE SEGMENT
• 24 operational satellites
orbiting the earth
• Arranged so that 4
satellites are placed in
each of the six orbital
planes
• 4 to 10 visible anywhere
in the world
• Circle the earth twice a
day
Components
Components
Components
CONTROL SEGMENT
• These control stations monitor and control the
information being sent by the satellites (time, orbit)
Components
Components
USER SEGMENT
• The user holds the GPS receiver that receives the
codes transmitted by the satellites. It must use this
information to calculate its position. Read on!
 Civilian
• Uses single frequency (L1)
• 1 code
 Military
• Uses two frequencies (L1/L2)
• 2 codes (determines time)
Components
Calculating a Position
SIGNALS
Satellites send out signals at different frequencies
(L1/L2)
Codes are used to transmit time
The receiver uses this information to calculate a
position through the following steps:
1. Determine distance
2. Position of satellites (orbit/ephemeris)
3. Triangulate
Components
1. Determine Distance
DISTANCE = VELOCITY X TIME DELAY
The signals travel through radio waves, therefore, they
travel the speed of light!
Velocity = Speed of light (186 000 miles/second)
The measured delay between the transmitted code and
the received code is the TIME DELAY.
Now the receiver can calculate the distance to the satellite.
BUT…WHERE are the satellites?
Components
1. Determine Distance
Components
2. Position of Satellites
Where are the satellites in space?
Without going into too much detail here…
The satellites send information about its:
1. Orbital Path (ephemeris) – indicates its position in its
elliptical path around the earth.
2. This is used to determine the position of the satellites
exact position relative to the earth (x,y,z)
Now the receiver has distance to satellites and position. It
needs to triangulate! Read on!
3. Triangulation
Components
A receiver will need the distance and position of at
least three satellites to get an accurate position.
Why?
D1
D2
Components
3. Triangulation
A receiver will need the distance and position of at
least three satellites to get an accurate position.
Why?
Components
3. Triangulation
A receiver will need the distance and position of at
least three satellites to get an accurate position.
Why?
Components
3. Triangulation
A receiver will need the distance and position of at
least three satellites to get an accurate position.
Why?
You’ve found
your position!
EARTH
Components
Still Confused?
Check out these webpages and/or downloadables:
WEBPAGES:
http://www.trimble.com/gps/how.html
http://www.garmin.com/aboutGPS/
http://www.magellangps.com/en/products/aboutgps/
DOWNLOADABLE from OUR site:
NOVAGPS9.exe – an executable that goes over triangulation
garminbeg.pdf – a beginner’s guide to GPS
Components
Research
From the websites and downloadable PDF document on the
following slide, find out the answers to the following:
1. Why do you think a fourth satellite may help in
triangulation.
2. What is selective availability?
3. What type of errors are inherent in GPS signals? Name
and explain at least four.
4. Explain Differential GPS? (DGPS)?
a) Why would you want it?
b) How does it work?
c) Name and explain three different ways of surveying
using GPS. Which one would be most accurate? Why?
Components
Research
4. Provide one case study of where GPS is used in Canada.
Incorporate a picture.
5. Find an article or two relating to GPS and the war in Iraq.
Use this article to explain how the coalition forces
(specifically U.S.) is using GPS in the war. Have they
encountered any problems? What did they have to think
about when they planned a “smart war” with Iraq? Anything
else you learned.