Introduction to Global Navigation Satellite Systems (GNSS) by nin62725

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									Introduction to Global
  Navigation Satellite
   Systems (GNSS)
  First Nations GIS Workshop
     December 9-10, 2008
       Travelodge, Ottawa
           A brief history…
• 1970s - first global GPS established by US
  DND.
• 1980s - NAVSTAR-GPS used by US DND
  and allies.
• 1983 - Korean Airlines flight 007 incident.
  Reagan made GPS available for public
  use.
… a brief history.
• 1994 - NAVSTAR came online for public use.
  – Selective Availability (SA) turned ON - differential
    correction required for accurate positions.
• 2000 - Clinton directed that SA be turned OFF.
• Today:
     •   Wide variety of receivers & features.
     •   Some multi-system receivers.
     •   20+ channels on most receivers.
     •   Improvements in satellite technology.
A GNSS has satellites and…




                    GPS Satellite              GPS Constellation
                                           (NAVStar has ~30 satellites)


Source: http://en.wikipedia.org/wiki/Gps
… position correction.
• Wide Area Augmentation
  System (WAAS) – free.
• Other correction systems:
   – European Geostationary
     Navigation Overlay
     Service. - free
   – Differential GPS (DGPS) $.
   – Inertial Navigation Systems
     (vehicles, missiles) $$.


                                   Source: http://en.wikipedia.org/wiki/Gps
      Global Navigation Satellite
          Systems (GNSS)
• GNSS-1
  – Primarily for military
  – NAVSTAR-GPS - US DND
       • Only GNSS currently operational
  – Global'naya Navigatsionnaya Sputnikovaya Sistema (GLONASS) -
    Russian Federation
       • To be restored by 2010
• GNSS-2
  –   Civilian navigation requirements
  –   Planned to be available by 2012
  –   GALILEO positioning system – EU
  –   Indian Regional Navigational Satellite System (IRNSS)
  –   COMPASS - China
                GPS Receivers
• All new receivers are WAAS enabled.
• Coordinates for position are calculated from GNSS data
  (satellite position and correction).
• Provide user with coordinates, time & direction.
• User can select local coordinate system and datum.
  Receiver calculates and displays.
• Data collected & stored on receiver using:
   – Geographic Coordinate System (GCS).
   – Latitude & Longitude in Decimal Degrees (DD).
   – Datum is World Geodetic System 1984 (WGS-84).
• Data must be downloaded, put into GIS format and is
  usually projected.
Receivers – Group 1          Garmin
                             eTrexH

• $150 - $500
• All have navigation.
• 3-5 metre accuracy in
  good conditions.            Garmin
                            Legend HCx
• Mid-range have mapping.
  Can load custom maps
  from GIS (not easily).
• Some have built-in
  camera and voice
  recorder.                  Magellan
                            Triton 2000
• Low to medium
  complexity.
Receivers – Group 2
• $1500 - $3000
• Mobile GIS (ArcPad,
                             Magellan
  PathAway, etc).          MobileMapper 6
• 3 m. accuracy in good
  conditions.
• Windows Mobile OS.
• Electronic forms, etc.       Trimble
• Medium to high              Juno SC

  complexity.
Receivers – Group 3
• $6000 - $10000
• Capable of sub-metre
  accuracy in good
                             Trimble Geo-XT
  conditions.
  – High accuracy
    requires a nearby GPS
    base station and post-
    processing.
• Windows Mobile O/S            Magellan
                             MobileMapper CX
• High complexity.
Receivers – Group 4
• $25,000 +
• Survey grade
  accuracy -
  millimetres.
• Very high complexity.

                                           Trimble Zephyrant



                               TopCon
                          Millimetre GPS
        Evaluating GPS Receivers
• Are desktop & receiver interface user-friendly?
    –   Windows CE gives software options (ArcPad, PathAway, etc.)
    –   Ease of importing background data (MapSource or NRVIS)
    –   Ease of data transfer.
    –   Is conversion required to get data into correct format?
• Is the receiver screen easily seen under a clear sky?
• Does the receiver meet military ruggedness?
• Type of batteries and expected life under normal use.
• User acceptance of receiver and desktop software.
• Consider the life of GPS receiver technology is about 3
  years.
• Suggest buying one receiver and evaluate it for 6
  months (all seasons).
  Factors Affecting Data Collection
Human                           Physical
                                • Water
• Personality
                                   – Vegetation density
   – Acceptance of technology      – Precipitation in air & on
   – Patience                        canopy
                                   – Human body
• Knowledge
                                • Structures & Vehicles
   – Training
                                   – error increases near
   – Experience                      concrete or metal
   – Understanding limits of    • Terrain
     GPS                           – Valley, base of cliff
   – Understanding GIS          • Atmosphere
     capabilities                  – Rain, clouds, ionosphere
More Factors
Timing                            System
• Time of year                    • Receiver clock errors.
   – Heavy dew on canopy in       • Orbital or ephemeris
     mornings                       errors.
   – Leafless period is best
                                  • Constellation
   – Dew is more of a problem
     in the late summer & early   • Intentional degradation of
     fall                           the satellite signal.
                        Considerations
         for GPS and Mobile GIS Projects
• Consult (or hire) a GIS specialist!
• Mapping scale affects target accuracy
   – 3 m. accuracy is adequate for 1:5000 or smaller
   – 7 m. accuracy is fine for 1:10000 or smaller
   – MNR has target of 10 m. accuracy for most values mapping.
• Check existing GPS collection standards & guidelines.
• Background data required for Mobile GIS.
   – MapSource, Fugawi NTS, custom geotiff.
• User preferences
   – Size of receiver, backpack with antenna.
• Temperature
   – Short battery life below freezing.
• Establish documentation procedures for field and post-processing.
               More Considerations
         for GPS and Mobile GIS Projects
• Features to be mapped
   – Point, line, polygon
• Improved accuracy with averaging positions.
   – 30 positions per point, 3 for line.
• Establish minimum polygon size and field capture methods.
   – If target accuracy is 10 m., then 20 m. is minimum width of the polygon
     feature to be mapped. Smaller areas will be lines or points depending
     on shape.
   – Use averaged points at significant locations to capture small polygons.
• Exporting GPS data to your GIS:
   – Desktop interface.
   – DNR GARMIN.
   – GPS Babel converts GPS data formats.
                Useful links
http://en.wikipedia.org/wiki/GPS
http://gauss.gge.unb.ca/manufact.htm
http://gpsinformation.us/main/whichgps.html
http://www.gpsnuts.com/myGPS/GPS/Technical/g
  ps_receiver_accuracy_by_c.htm
http://www.dnr.state.mn.us/mis/gis/tools/arcview/e
  xtensions/DNRGarmin/DNRGarmin.html
http://www.gpsbabel.org/
Questions?
Ted Hiscock, GIS Officer
Pembroke District
Ontario Ministry of Natural Resources
31 Riverside Drive
Pembroke, ON K8A 8R6

(613)732-5512
ted.hiscock@ontario.ca

								
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