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GPS technology and how it works!

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  1. 1. Introduction to the Global Positioning System by Dr. Stephen C. Brown K-State Research and Extension Brown County And Mandy Kern Hiawatha High Agriculture Educator
  2. 2. WHAT IS GPS?• Satellite based radio positioning system• Developed and maintained by the U.S. Department of Defense• Made up of three segments: Space Control User or Ground receivers• Used for obtaining accurate locations anywhere on earth
  3. 3. Space Segment
  4. 4. GPS Is An Excellent Mapping ToolInstantly gives: Altitude Speed Longitude and Latitude
  5. 5. How It Works….Trilateration
  6. 6. Math Connection Step 1 •Suppose we measure our distance from a satellite and find it to be 11,000 miles. •Knowing that were 11,000 miles from a particular satellite narrows down all the possible locations we could be in the whole universe to the surface of a sphere that is centered on this satellite and has a radius of 11,000 miles.
  7. 7. Math Connection Step 2 •Next, say we measure our distance to a second satellite and find out that its 12,000 miles away. • That tells us that were not only on the first sphere but were also on a sphere thats 12,000 miles from the second satellite. Or in other words, were somewhere on the circle where these two spheres intersect.
  8. 8. Math Connection Step 3•If we then make ameasurement from a thirdsatellite and find that were13,000 miles from that one,that narrows our position downeven further to the two pointswhere the 13,000 mile spherecuts through the intersection ofthe first two spheres. •To decide which one is our true location we could make a fourth•So by ranging from three measurement. But usually one ofsatellites we can narrow our the two points is a ridiculousposition to just two points in answer (either too far from Earth orspace. moving at an impossible velocity) and can be rejected without a measurement.
  10. 10. Control Segment• Maintained by the Department of Defense
  11. 11. Sources of Error Selective Availability (SA Error) Atmospheric SV Ephemeris Multipathing Poor SV Geometry
  12. 12. EPE (Estimated Position Error)The higher the EPE,the greater thePositioning error!Good EPE’s range from 10-20 feet.Proper pre-mission planning prevents poor positioning!
  13. 13. Shape of the Earth (datum)
  14. 14. PRACTICAL APPLICATIONS•Navigation •Sailing, hiking and aviation •Collecting and locating way-points•Locating Features • Stocking locations or stream surveys • Endangered or sensitive species locations • Locating trails or physical structures•GIS •Collecting GPS data along with attribute data • Mapping and database update•Surveying •Locating Control Points quickly
  15. 15. LOW END UNITS•Capabilities •20 ft accuracy •1-12 channel receiver •Collect only way point data•Cost •$80 - $600•Limitations •Poor reception under tree canopy •No file collection•Applications •Navigation for hiking or sailing
  16. 16. MID-RANGE UNITS•Capabilities • Sub-meter accuracy with DGPS • 6-12 channel receiver • Collects static, mobile and attribute data•Cost • $2,500 - $15,000•Limitations •Not accurate for surveying•Applications • Navigation • Mapping •GIS Update
  17. 17. HIGH END UNITS•Capabilities • cm accuracy with DGPS • 12 channel receiver • Collects static points•Cost • $15,000 - $100,000•Applications • Surveying
  18. 18. Garmin GPS Receivers Inexpensive and downloadable Available locally for less than $150 Most GPS receivers similar in operation
  19. 19. Okay, lets see how it works!Zoom out/in Page ButtonButton Power Button Find ButtonThumbstick
  20. 20. Pages In the GPS Unit
  21. 21. SV Visibilityclear view obstructed viewclear view obstructed view
  22. 22. Satellite Status Page Satellite status appears while the unit “finds” the satellites Acquisition can take several minutes
  23. 23. Satellite Status PageSatellite elevation/position Signal strength Receiver position
  24. 24. Main Page The main page allows user to edit waypoints, tracks and routes or configure system to personal preference
  25. 25. Map Page Allows you to view map of current location, waypoints and tracks
  26. 26. Waypoints4 track 2 3 waypoint 1
  27. 27. Creating Waypoints Marking waypoints allows you to remember and return to a specific location Waypoints are created by pressing and holding thumbstick
  28. 28. Finding Waypoints Pressing “Find” button will bring up a list of waypoints Entering a waypoint will result in “as the crow flies” directions to that
  29. 29. Finding Waypoints Name of WaypointDistance to WaypointBearing to Waypoint Heading Speed
  30. 30. What is Geocaching?Geocaching is a worldwide “scavenger hunt”using GPS to find “caches” of treasure. Theonly rules are to leave something if you take something and do not disturb the cache
  31. 31. Links to using GPS into the Classroom
  32. 32. Let’s Practice!! Waypoint #1 – N 39°51.102 W 095°31.536 Waypoint #2 – N 39°51.081 W 095°31.590 Waypoint #3 – N 39°51.113 W 095°31.417 Waypoint #4 – N 39°51.090 W 095°31.400