Transcript An Introduction to the Global Positioning System

Introduction
To GPS
Earth
Circumference
 24,900 Miles
Rotation
 1,038
Miles/Hour
 1 Day Cycle
Moon
1/4 Size of the
Earth
Distance from
Earth
239,000 Miles
The History of GPS
Feasibility studies begun in 1960’s.
 Pentagon appropriates funding in
1973.
 First satellite launched in 1978.
 System declared fully operational
in April, 1995.
 Open to the public, 2000.
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How does GPS work?
 Stations
on earth, and a GPS
receiver, the distances between
each of these points can be
calculated.
 The
distance is calculated based
on the amount of time it takes for
a radio signal to travel between
these points.
 Using
satellites in the sky,
ground allows the GPS receiver
to know where you are, in terms
of latitude and longitude, on the
earth.
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The more satellites the GPSr can “see”, the more accurate your
reading.
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The GPSr must “see” the satellites, so it does not work well in dense
forests, inside caves, underwater, or inside buildings.
Components of the System
User segment
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GPS antennas & receiver/processors
Position
Velocity
Precise timing
Used by
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Aircraft
Ground vehicles
Ships
Individuals
Handheld GPS Receivers
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Garmin eTrex
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Garmin-12
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~$150
Casio GPS
wristwatch
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~$100
~$300
The GPS Store
GPS Satellite Vehicle
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Four atomic clocks
Three nickel-cadmium
batteries
Two solar panels
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Battery charging
Power generation
1136 watts
S band antenna—satellite
control
12 element L band antenna—
user communication
Block IIF satellite vehicle
(fourth generation)
GPS Satellites
Distance from
Earth
12,000 Miles
2 Orbits in 24
Hours
Travel 7,000
MPH
Powered by Solar
Energy
Satellites
GPS satellites are controlled and
operated by the Dept. of Defense.
24 satellites in orbit dedicated to GPS.
6 satellites are within view of any
location at one time, provided that
physical terrain, or structures do not
block them.
Satellites constantly transmit their
locational information and time data.
Slide 28
Space
 24 satellites
 12,000 miles above Earth
 Orbit twice daily
 At least 4 satellites in
view
 Distance from Earth to
Moon - 256,000 miles
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User
Segment
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.
What does a GPS receiver do?
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GPS receiver allows you to pinpoint your
location, anywhere in the world, based on
latitude and longitude coordinates.
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It can tell you in what direction you are heading.
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It can show you:
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how fast you are going
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your altitude
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a map to help you arrive at a destination
Signal From One Satellite
The receiver is
somewhere on
this sphere.
Signals From Two Satellites
Three Satellites
(2D Positioning)
Three Dimensional
(3D) Positioning
System Performance
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Standard Positioning
System
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100 meters horizontal accuracy
156 meters vertical accuracy
Designed for civilian use
No user fee or restrictions
Precise Positioning
System
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22 meters horizontal accuracy
27.7 meters vertical accuracy
Designed for military use
Real Time Differential GPS
x+5, y-3
x+30, y+60
x-5, y+3
Receiver
DGPS Receiver
DGPS correction = x+(30-5) and
y+(60+3)
DGPS Site
True coordinates =
x+0, y+0
True coordinates = x+25, y+63
Correction = x-5, y+3
How GPS Works
Okay, you’re lost, you have
amnesia, and you have
absolutely no idea where you
are. You go up to someone,
and like a good amnesiac
you ask, “Where Am I?” This
person tells you that you are
625 miles from Boise, Idaho.
You say, sarcastically, “Wow,
that’s some great
information. Thanks Buddy.”
We’re Getting Closer
You still have absolutely no
idea where you are, so once
again you go up to someone
and ask, “Where Am I?” This
person tells you that you’re
690 miles from Minneapolis.
You just scratch your head,
but then you start to
remember what you learned in
GPS class, and, with the US
map in your pocket to guide
you, you proceed.
Now We Know!
You see a another smiling face
and ask “where am I” one
more time. This time you get
the reply “you are 615 miles
from Tucson. The light pops
on in your brain. It’s all clear
now. You draw three circles
extending in the radii of 625
miles from Boise, 690 from
Minneapolis, and 615 miles
from Tucson. The circles
intersect in Denver! Aren’t you
glad that you took this class?
GPS by Trilateration
GPS Distance D = Speed of Light x Time;
or D = CT
D
Sources of Signal Interference
Earth’s Atmosphere
Solid Structures
Metal
Electro-magnetic Fields
Obstruction
Waypoint
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A waypoint is based on coordinates entered
into a GPS receiver’s memory.
It can be either a saved position fix, or user
entered coordinates.
It can be created for any remote point on earth.
It must have a receiver designated code or
number, or a user supplied name.
Once entered and saved, a waypoint remains
unchanged in the receiver’s memory until
edited or deleted.
Planning a Navigation Route
Start
= Waypoint
How A Receiver Sees Your
Route
What is Geocaching?
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All around the world, people have hidden “caches”
and posted the coordinates on a website.
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Anyone can go on the site and write down or
download the coordinates of the cache to their GPS
and go find it.
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Once you have found a cache, you can go on the
site and report your findings
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This activity started in May of 2000, when the
government lifted the “Selective Availability” of the
GPS signals so that consumer GPS devices where
as accurate at the military devices.
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There are over 300,00 active caches in 222
countries.
How do I start to Geocache?
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Go to www.geocaching.com (or other geocache site)
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Click on “Hide and Seek”
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Enter a zip code, city and state or coordinates near
where you want to hunt.
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Note the level of difficulty, the type of cache and when
it was last found.
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Once you have selected a cache to hunt for, you can:
 Download
or manually enter the “waypoint” to
your GPS
 Print
logs
out the page with the coordinates, hint and
Types of Caches
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Traditional caches- can be any size;
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usually have a log book or paper and a pencil for you to
sign
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trinkets or items to trade with items you have brought
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May contain a “Travel Bug”
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Micro caches- small containers, such as film canisters or
magnetic key cases; usually only have a log in them for you to
sign
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Virtual Caches- The spot is the cache itself. May be a historic
site, a place with a unique activity, or scenic sights.
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Multi-tier caches- have clues inside for you to follow to get to
the next cache which may lead to another cache
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Benchmarks- these are permanent markers placed around the
US government for surveying purposes. Some people enjoy
seeing how many of these markers they can find.
Geocaching Sites
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Geocaching.com http://www.geocaching.com - Number 1 site for geocaching;
the one that started it all
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Navicache.com http://www.navicache.com - Number 2 web site for geocaching
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Geocacher’s Creed http://www.geocreed.info/
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Today’s Cacher http://www.todayscacher.com - online magazine for
geocachers
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Geocacher University http://www.geocacher-u.com
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Markwell’s FAQ’s
http://members.aol.com/_ht_a/marklent60544/myhomepage/Geocaching/markw
ellgcfaq.htm
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Buxley's Geocaching Waypoint http://brillig.com/geocaching
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KeenPeople.com http://www.keenpeople.com
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The First 100 Geocaches http://members.cox.net/pkpublic/index.html
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Geocaching with Kids http://www.eduscapes.com/geocaching/kids.htm
Educational Resources
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From a Distance- NASA site with Information and Lesson
Plans http://wwwedu.ssc.nasa.gov/fad/default.asp
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All About GPS (tutorial) http://www.trimble.com/gps/index.html
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GIS and GPS Lesson Plan Resources
http://www.gis2gps.com/GIS/lessons/lessons.html
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What is Latitude and Longitude
http://www.rain.org/campinternet/gis/gis-lat-long-whatis.html
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How GPS Receivers Work
http://electronics.howstuffworks.com/gps.htm
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GPS Guide for Beginners (PDF download)
http://www.garmin.com/aboutGPS/manual.html
Sites of similar
activities
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Letterboxing http://www.letterboxing.org/
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Bookcrossing http://www.bookcrossing.com/
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GPS Drawing http://www.gpsdrawing.com/info.htm
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Benchmarking or Benchmark hunting
http://www.ngs.noaa.gov
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Degree Confluence Project
http://www.confluence.org/index.php
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GPS Games http://www.gpsgames.org/
Citations
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Dixon, Conrad. Using GPS. 2nd ed. Dobbs
Ferry: Sheridan House, 1999.
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Letham, Lawrence. GPS Made Easy. Seattle:
The Mountaineers, 1996.
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McNamara, Joel. Geocaching for Dummies.
Hoboken: Wiley Publishing, 2004.