GPS Receivers

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GPS Receivers

• University of Manitoba
• Recreation Services GPS Workshop.

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What is GPS?

• GPS is the acronym for
• Global Positioning System.
• GPS consists of a series of
• satellites (24) that transmit data that allow
  receivers on Earth to determine their location
  with great accuracy. Also included in this
  system are ground stations (5) that are used for
  detecting and updating errors. Generally we only
  think about the receivers and call those a GPS or
  GPS units.

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The Short Story!

• GPS Receiver (Hand Held Unit)
• Triangulation with at least 3 satellites a
  good view of the sky (4 satellites needed for X,
  Y and Z coordinates)
• How accurate?
• 10-20m (elevation 2x horizontal error)
• 0.5cm with additional equipment

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Where You Are - Triangulation

• 1 satellite

• 2 satellites

• 3 satellites (Lat/Long 2D)
• 4 satellites gives altitude

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Enhancements to Accuracy (WAAS)

• Wide Area Augmentation System
• Geo-stationary Satellites
• 25 ground stations of known location (North
  America)
• corrects for GPS signal errors caused by
  ionospheric disturbances, timing and satellite
  orbit errors
• Improves accuracy to 3-5m
• Limits
• Must have good view of sky
• Antenna/receiver must be powered all of the time.

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Enhancements to Accuracy (DGPS)

• Differential GPS involves the cooperation of two
  receivers, one that's stationary and another
  that's roving around making position
  measurements. The stationary receiver is the
  key.  It ties all the satellite measurements into
  a true known position.

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DGPS Accuracy

• 1-3 meter with U.S. Coast Guard signal
• 0.5 cm with local base station (used extensively
  in Westside farming)

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Limitations for Hiking

• Need to see the sky!
• Trees, buildings, mountains, some car
  windshields, etc...
• Only indicates place not movement or direction
• So how does it measure speed and direction?
• Minimum speed 1.5km/hour (some up to 4km/hour)
• Power
• Bring extra batteries
• Cold/Winter Temperatures
• Power
• LCD Screen

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Sources of Error (10m)

• Measures (some receivers display)
• DOP (dilution of precision)
• EPE (Estimate Position Error)
• Minimize Error
• Averaging
• Better Satellite Config
• Move to get better sky view
• Re-orient receiver (patch/helix)
• Wait ?

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Of Datums and Coordinates

• Datum
• NAD27 (Canada), NAD83, WGS84
• Co-ordinate
• Lat/Long (dd.dddd, ddhhmm.ss) N4952'10.11"
  W09713'45.95"
• UTM/UPS (Zone Easting Northing)
  14U 627231 5525622
• MGRS (Zone GridRef Easting Northing)
  14U PA 27231 25622

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Some Terms

• WayPoint
• Bearing
• Track (log)
• Route

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Cost 100-50,000

• Based mostly on the need for accuracy

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GPS Applications in Agriculture

• Determine field boundaries
• Crop scouting (maturation, weeds, pests)
• Soil testing
• Tillage
• Spraying (pesticides, herbicides, fertilizers)
• Yield monitoring