AN  INTRODUCTION  TOGPS  FOR  GEOCACHERS<br />PRESENTED  BY :-<br />TUHIN  DAS<br />
WHAT IS GEOCACHING?<br />“Geocaching is a sport where you use a multi billion dollar satellite system to locate rubbermaid...
GLOBAL  POSITIONING  SYSTEM (GPS)<br />GPS was developed by US DoD and is managed by the US Air Force<br />$750 million an...
THREE SEGMENTS<br />Space Segment<br />Minimum of 24 satellites (currently 30) in orbit around Earth at altitude 20,000 km...
TRANSMITTED SIGNALS<br />Each satellite transmits:<br />It’s approximate position<br />Exact orbit and location<br />Navig...
Your position<br />The Simple View<br />Knowing how far you are from at least three fixed positions, you can determine you...
EXACT POSITION<br />Using three satellites, you should be able to determine exact position but other factors prevent “pref...
POSITION  ERROR<br />Position (Uncertainty) Error<br />GPSr will display uncertainty values<br />
OTHER DATA<br />With multiple satellites can get altitude<br />As you move, a GPSr will calculate<br />Velocity<br />Cours...
SELECTIVE  AVAILABILITY  & GEOCACHING<br />Prior to May 2000, civilian GPS signal included a random error (Selective Avail...
TRANSMITTED SIGNALS<br />Each satellite transmits ephemeris, almanac and navigation data<br />Almanac data – coarse orbit ...
EXACT POSITION<br />Using three satellites, you should be able to determine exact position but other factors prevent “pref...
BUT HOW DO YOU GET DISTANCE?<br />Satellites have atomic clock<br />GPSr has accurate internal clock<br />Each satellite’s...
COMPARING SEQUENCES<br />GPSr Sequence<br />Satellite Sequence<br />Time Offset x Speed Of Light = Distance From Satellite...
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Presentation On Gps

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G P S STANDS FOR GLOBAL POSITIONING SYSTEM........

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Presentation On Gps

  1. 1. AN INTRODUCTION TOGPS FOR GEOCACHERS<br />PRESENTED BY :-<br />TUHIN DAS<br />
  2. 2. WHAT IS GEOCACHING?<br />“Geocaching is a sport where you use a multi billion dollar satellite system to locate rubbermaid containers in the middle of the woods.”<br />- Anonymous<br />
  3. 3. GLOBAL POSITIONING SYSTEM (GPS)<br />GPS was developed by US DoD and is managed by the US Air Force<br />$750 million annual cost to operate<br />Now widely used in the civilian sector as well as military users<br />Surveying<br />Geology<br />Hiking<br />Maritime<br />Airlines<br />And on and on…<br />
  4. 4. THREE SEGMENTS<br />Space Segment<br />Minimum of 24 satellites (currently 30) in orbit around Earth at altitude 20,000 km<br />Control Segment<br />Satellites are tracked by ground stations<br />Navigation updates sent to satellites<br />Updates ephemeris data (position) and atomic clocks<br />User Segment<br />GPS Receiver<br />Uses data from satellites to calculate user’s position, altitude and other data<br />
  5. 5. TRANSMITTED SIGNALS<br />Each satellite transmits:<br />It’s approximate position<br />Exact orbit and location<br />Navigation signal<br />Civilian<br />Military (more precise) <br />
  6. 6. Your position<br />The Simple View<br />Knowing how far you are from at least three fixed positions, you can determine your position (triangulation)<br />GPS Technology actually uses trilaterilization<br />
  7. 7. EXACT POSITION<br />Using three satellites, you should be able to determine exact position but other factors prevent “prefect” overlap<br />Atmospheric interference<br />Buildings<br />Trees, etc<br />Using additional satellites, the GPSr attempts to reconcile position by adjusting the offsets<br />Same “interference” for all signals<br />
  8. 8. POSITION ERROR<br />Position (Uncertainty) Error<br />GPSr will display uncertainty values<br />
  9. 9. OTHER DATA<br />With multiple satellites can get altitude<br />As you move, a GPSr will calculate<br />Velocity<br />Course<br />Track (“bread crumbs”)<br />Distance & Heading to marked position<br />Elapsed time, average, speed, etc<br />
  10. 10. SELECTIVE AVAILABILITY & GEOCACHING<br />Prior to May 2000, civilian GPS signal included a random error (Selective Availability)<br />Civilian accuracy &gt;30m<br />Pres. Clinton turned off SA at 0000, 1 May 2000<br />Resulted in accuracy &lt; 10m<br />Benefit sportsmen, FAA, etc<br />3 May 2000 - Dave Ulmer placed first “cache”<br />Now over 400,000 caches worldwide!<br />
  11. 11. TRANSMITTED SIGNALS<br />Each satellite transmits ephemeris, almanac and navigation data<br />Almanac data – coarse orbit & status info for all satellites<br />Ephemeris – specific orbit and position data<br />Navigation – Unique code every millisecond<br />C/A (Coarse/Acquisition) – Civilian<br />Encrypted P(Y) (Precision) - Military<br />
  12. 12. EXACT POSITION<br />Using three satellites, you should be able to determine exact position but other factors prevent “prefect” overlap<br />Atmospheric interference<br />Buildings<br />Trees, etc<br />Using additional satellites, the GPSr attempts to reconcile position by adjusting the offsets<br />Same “interference” for all signals<br />
  13. 13. BUT HOW DO YOU GET DISTANCE?<br />Satellites have atomic clock<br />GPSr has accurate internal clock<br />Each satellite’s C/A code is a unique string<br />Allows for reception of signals from multiple satellites on same frequency<br />GPSr reproduces each C/A code internally<br />GPSr “lines up” the two sequences, and based on the offset, you can determine distance to satellite<br />
  14. 14. COMPARING SEQUENCES<br />GPSr Sequence<br />Satellite Sequence<br />Time Offset x Speed Of Light = Distance From Satellite<br />Since you know the position of the satellite, and the distance from that satellite, you now have a sphere, centered on the satellite, you can be on<br />

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