GPS ReceiversGPS Receivers

• University of ManitobaUniversity of Manitoba

• Recreation Services Recreation Services GPS Workshop. GPS Workshop.

What is GPS?What is GPS?

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

The Short Story!The Short Story!

• GPS Receiver (Hand Held Unit)GPS Receiver (Hand Held Unit)

• Triangulation with at least 3 satellitesTriangulation with at least 3 satellites & a good view of the sky (4 satellites & a good view of the sky (4 satellites needed for X, Y and Z coordinates)needed for X, Y and Z coordinates)

• How accurate?How accurate?– ±±10-20m (elevation ~ 10-20m (elevation ~ ±±2x horizontal 2x horizontal

error) error) – 0.5cm with additional equipment0.5cm with additional equipment

Where You Are - Where You Are - TriangulationTriangulation

• 1 satellite1 satellite

• 2 satellites2 satellites• 3 satellites (Lat/Long 2D)3 satellites (Lat/Long 2D)

• 4 satellites gives altitude4 satellites gives altitude

Enhancements to Accuracy Enhancements to Accuracy (WAAS)(WAAS)

• Wide Area Augmentation SystemWide Area Augmentation System– Geo-stationary SatellitesGeo-stationary Satellites– ~25 ground stations of ~25 ground stations of

known location (North America)known location (North America)– corrects for GPS signal errors caused by corrects for GPS signal errors caused by

ionospheric disturbances, timing and ionospheric disturbances, timing and satellite orbit errors satellite orbit errors

– Improves accuracy to 3-5mImproves accuracy to 3-5m– Limits Limits

• Must have good view of skyMust have good view of sky

• Antenna/receiver must be powered all of the Antenna/receiver must be powered all of the time.time.

Enhancements to Accuracy Enhancements to Accuracy (DGPS)(DGPS)

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

DGPS AccuracyDGPS Accuracy

• 1-3 meter with U.S. Coast Guard 1-3 meter with U.S. Coast Guard signalsignal

• 0.5 cm with local base station (used 0.5 cm with local base station (used extensively in Westside farming)extensively in Westside farming)

Limitations for HikingLimitations for Hiking• Need to see the sky!Need to see the sky!

– Trees, buildings, mountains, some car windshields, Trees, buildings, mountains, some car windshields, etc...etc...

• Only indicates place not movement or directionOnly indicates place not movement or direction– So how does it measure speed and direction?So how does it measure speed and direction?– Minimum speed ~1.5km/hour (some up to Minimum speed ~1.5km/hour (some up to

4km/hour)4km/hour)

• PowerPower– Bring extra batteriesBring extra batteries

• Cold/Winter TemperaturesCold/Winter Temperatures– PowerPower– LCD ScreenLCD Screen

Sources of Error (~10m)Sources of Error (~10m)• Measures Measures (some receivers (some receivers

display)display)

– DOP DOP (dilution of precision) (dilution of precision)

– EPE EPE (Estimate Position Error)(Estimate Position Error)

• Minimize ErrorMinimize Error– AveragingAveraging– Better Satellite ConfigBetter Satellite Config– Move to get better sky Move to get better sky

viewview– Re-orient receiver Re-orient receiver

(patch/helix)(patch/helix)

– Wait Wait

Error Value

Ionosphere 4.0 meters

Clock 2.1 meters

Ephemeris 2.1 meters

Troposphere 0.7 meters

Receiver 0.5 meters

Multipath 1.0 meter

Total 10.4 meters

Of Datums and CoordinatesOf Datums and Coordinates

• DatumDatum– NAD27 (Canada), NAD83, NAD27 (Canada), NAD83, WGS84WGS84

• Co-ordinateCo-ordinate– Lat/Long (dd.dddd, ddLat/Long (dd.dddd, dd°°hh’mm.ss”)hh’mm.ss”)

N49°52'10.11" W097°13'45.95"N49°52'10.11" W097°13'45.95"– UTM/UPS (Zone Easting Northing)UTM/UPS (Zone Easting Northing)

14U14U 627231627231 55256225525622 – MGRS (Zone GridRef Easting Northing)MGRS (Zone GridRef Easting Northing)

14U14U PAPA 2723127231 2562225622

Some TermsSome Terms• WayPointWayPoint

• BearingBearing

• Track (log)Track (log)

• RouteRoute

Cost: $100-50,000Cost: $100-50,000

• Based mostly on the need for Based mostly on the need for accuracyaccuracy

GPS Applications in GPS Applications in AgricultureAgriculture• Determine field boundariesDetermine field boundaries

• Crop scouting (maturation, weeds, Crop scouting (maturation, weeds, pests)pests)

• Soil testingSoil testing

• TillageTillage

• Spraying (pesticides, herbicides, Spraying (pesticides, herbicides, fertilizers)fertilizers)

• Yield monitoringYield monitoring