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Introduction

Introduction. Summary of Topics. - GPS - WAAS - Coordinate Systems - Datums. A Brief History Of GPS. 1973 – U.S. Air Force tasked with initial development 1980’s – First civilian use 1995 – GPS declared “Fully Operational” 2000 – “Selective Availability” suspended

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Introduction

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  1. Introduction

  2. Summary of Topics - GPS - WAAS - Coordinate Systems - Datums

  3. A Brief History Of GPS • 1973 – U.S. Air Force tasked with initial development • 1980’s – First civilian use • 1995 – GPS declared “Fully Operational” • 2000 – “Selective Availability” suspended • Today – Wide variety of products and services utilize GPS technology, and the European Union builds its own GPS

  4. Apply GPS To Fire Situations • Report a fire’s location • Navigate to a fire’s reported location • Map a fire’s point of origin, or its perimeter • Locate a safety zone, helispot, pump, water source, or other point of interest • Map roads or trails to be used for access • Map resources or improvements to be protected • Map dozer line to be rehabilitated • Document search, rescue, or recovery efforts

  5. How does GPS work?

  6. The Global Positioning System Space Segment User Segment Control Segment

  7. Master Control Station Monitor Station Ground Antenna Control Segment US Space Command Cape Canaveral Hawaii Kwajalein Atoll Diego Garcia Ascension Is.

  8. The Space Segment 24 or more satellites in Earth orbit that transmit: • PRN code • Ephemeris data • Atmospheric data • Clock information • An almanac

  9. JTrack http://liftoff.msfc.nasa.gov/RealTime/JTrack/3D/JTrack3D.html Altitude 20,200 km 10,900 nm

  10. Earth in a Cage of Satellites Current: Satellites 1 - 32 Max: 32 Satellites

  11. 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

  12. How to Calculate a Position Measure the Distance to the Satellites

  13. How to Calculate Distance Speed of Light x Travel Time Distance Time signal left satellite Time current

  14. Minimum # of Satellites Required-Algebra Problem Unknown time latitude longitude elevation Equation satellite location 4 Unknowns We Need 4 Satellites

  15. Minimum # of Satellites Required-Trilateration 1 satellite – somewhere on a sphere

  16. Minimum # of Satellites Required-Trilateration 2 satellites – somewhere on a circle

  17. Minimum # of Satellites Required-Trilateration 3 satellites – one of two points

  18. Minimum # of Satellites Required-Trilateration 4 satellites – one point 3D GPS Location Note: with 3 satellites, one point is on the earth’s surface and one is nowhere near. However, we still need the 4th satellite because receiver clocks are inaccurate.

  19. When There are Only 3 Satellites • 2D GPS Location • Elevation - last known • 2-5 X Error Rule

  20. DOPs TDOP VDOP HDOP PDOP GDOP Garmin Estimated Accuracy Relies on Dilution of Precision -Want tetrahedron as large as possible - Want index as low as possible

  21. Ideal Satellite Geometry N E W S

  22. Good Satellite Geometry

  23. Poor Satellite Geometry N W E S

  24. Poor Satellite Geometry

  25. Positions Recorded by Stationary GPS Receiver Garmin GPSmap76S 1 position/second 10 minutes WAAS Disabled 3.1 meters 3.6 meters

  26. Errors(tens of meters) Ionosphere Troposphere Satellite Clock Errors Satellite Ephemeris Errors Multipath Receiver Noise

  27. x+5, y-3 x+30, y+60 x-5, y+3 Receiver DGPS Receiver DGPS Site Real Time Differential GPS True coordinates = x+0, y+0 Correction = x-5, y+3 DGPS correction = x+(30-5) and y+(60+3) True coordinates = x+25, y+63

  28. Wide Area Augmentation System GPS Constellation WAAS satellites WAAS Control Station(Position known) GPS receiver(Position with errors) 25 Reference Stations (Position known)

  29. WAAS Wide Area Augmentation System WAAS Satellite

  30. Errors Reduced by WAAS Correction(multi-meter) Ionosphere Troposphere Satellite Clock Errors Satellite Ephemeris Errors Multipath Receiver Noise

  31. Receiving WAAS Correction If WAAS signal intermittent- WAAS correction for SV 19 No WAAS correction for SV 11

  32. Caution! If WAAS Enabled – - 2D WAAS chosen over 3D uncorrected - WAAS chosen over DOP Recommendation If WAAS signal intermittent (example: under canopy) - disable WAAS

  33. Signal Disruption Ionosphere SolidStructures Electro-magnetic Fields Metal

  34. Good Data Collection Techniques External Antenna Map76S more accurate under canopy Sleeve Mounts Vehicle Brackets

  35. Map Projections & Coordinate Systems

  36. Projecting a Sphere Onto a Plane Three-dimensional sphere to two-dimensional flat map.

  37. Examples of Several Projections Depending on the projection, a certain amount of distortion occurs when portraying the earth on paper.

  38. Coordinate Systems (Projections) We Use – 2 Coordinate Systems Latitude / Longitude Universal Transverse Mercator (UTM) Garmin - 29 Location Formats

  39. Latitude & Longitude PrimeMeridian (Longitude) 30º N 10º N 0º 0º 10º S Equator (Latitude) PointofOrigin

  40. ParallelsofLatitude 20º N 10º N 10º 690 miles 0º N 10º 690miles 10º S 10º 690miles

  41. Meridians of Longitude 10º ToNorthPole 240 mi 10º 460 miles Equator 10º 690 miles ToSouthPole 110º W 120º W

  42. Three Ways To Express Latitude / Longitudeon a Garmin

  43. Three Ways To Express Latitude / Longitude(for the Same Location) hddd.ddddd° Degrees (Decimal Degrees) N 43.68216°, W 116.28725° hddd° mm.mmm’ Degrees-Minutes (Decimal Minutes)N 43° 40.930’, W 116° 17.235’ hddd° mm’ ss.s” Degrees-Minutes-Seconds (Decimal Seconds)N 43°40’ 55.8”, W 116°17’ 14.1”

  44. Coordinate Systems hddd0 mm.mmm’: N 43040.93’ X W 1160 17.235’ (40.93’/ 60 =.682160) hddd.ddddd0 : N 43.682160 X W 116.287250 Different coordinates representing the same location: hddd0 mm’ ss.s”: N 430 40’ 55.8” X W 1160 17’ 14.1” (55.8”/ 60 =.93’) UTM/UPS: 11T 0557442m E 4836621m N

  45. Example: Error in Latitude 35° 24´ 45˝ N 35° 24.450’ N 1/3 of a mile

  46. 1 degree 1 degree Lat / Long Shortcomings ? 1 minute + + ? ? +

  47. Universal Transverse Mercator • measured in meters • located in zones (1 - 60) • include northing and easting • are positive Zone Easting Northing Latitude Band Coordinates

  48. UTM Zones in the Lower 48 19 10 11 12 18 13 17 16 14 15 UTM Zones

  49. UTM Grid Overlay 21 84º N X W V U T T S R 21 T Q P Latitude Bands N M L K J H G F E D C 80º S 60 Zones, and 20 Latitude Bands Zones 1 60 Equator

  50. UTM Latitude Band We Use – 2 GIS choices UTM Zone _ North UTM Zone _ South Latitude Band Garmin Uses – UTM bands Bands C - M, southern hemisphere Bands N - X, northern hemisphere no “I” no “O”

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