IntroductionIntroduction

Summary of TopicsSummary of Topics

- GPS- GPS

- WAAS- WAAS

- Coordinate Systems- Coordinate Systems

- Datums- Datums

• 1973 – U.S. Air Force tasked with initial 1973 – U.S. Air Force tasked with initial developmentdevelopment

• 1980’s – First civilian use1980’s – First civilian use• 1995 – GPS declared “Fully Operational”1995 – GPS declared “Fully Operational”• 2000 – “Selective Availability” suspended2000 – “Selective Availability” suspended• Today – Wide variety of products and Today – Wide variety of products and

services utilize GPS technology, and the services utilize GPS technology, and the European Union builds its own GPSEuropean Union builds its own GPS

A Brief History Of GPSA Brief History Of GPS

Apply GPS To Fire SituationsApply GPS To Fire Situations• Report a fire’s locationReport a fire’s location• Navigate to a fire’s reported locationNavigate to a fire’s reported location• Map a fire’s point of origin, or its perimeterMap a fire’s point of origin, or its perimeter• Locate a safety zone, helispot, pump, water Locate a safety zone, helispot, pump, water

source, or other point of interestsource, or other point of interest• Map roads or trails to be used for accessMap roads or trails to be used for access• Map resources or improvements to be protectedMap resources or improvements to be protected• Map dozer line to be rehabilitatedMap dozer line to be rehabilitated• Document search, rescue, or recovery effortsDocument search, rescue, or recovery efforts

How does GPS work?How does GPS work?

The Global Positioning System The Global Positioning System

Control Segment

Space Segment User

Segment

Kwajalein Atoll

US Space Command

Control SegmentControl SegmentControl SegmentControl Segment

Hawaii

Ascension Is.

Diego Garcia

Cape Canaveral

Ground AntennaGround Antenna

Master Control StationMaster Control Station

Monitor StationMonitor Station

The Space SegmentThe Space Segment

24 or more satellites in 24 or more satellites in Earth orbit that Earth orbit that transmit:transmit:•PRN codePRN code•Ephemeris dataEphemeris data•Atmospheric dataAtmospheric data•Clock informationClock information•An almanacAn almanac

JTrackJTrackJTrackJTrack

http://liftoff.msfc.nasa.gov/RealTime/JTrack/3D/JTrack3D.html

AltitudeAltitude

20,200 km 20,200 km

10,900 nm10,900 nm

Earth in a Cage of Satellites Earth in a Cage of Satellites

Current:Current: Satellites 1 - 32Satellites 1 - 32Max:Max: 32 Satellites32 Satellites

MilitaryMilitary Search and rescueSearch and rescue Disaster reliefDisaster relief SurveyingSurveying Marine, aeronautical and terrestrial navigationMarine, aeronautical and terrestrial navigation Remote controlled vehicle and robot guidanceRemote controlled vehicle and robot guidance Satellite positioning and trackingSatellite positioning and tracking ShippingShipping Geographic Information Systems (GIS)Geographic Information Systems (GIS) RecreationRecreation

User SegmentUser Segment

How to Calculate a PositionHow to Calculate a Position

Measure the Distance to the Satellites

How to Calculate DistanceHow to Calculate Distance

Speed of Light x Travel Time

Distance

Time signal left satelliteTime signal left satellite

Time currentTime current

Minimum # of Satellites RequiredMinimum # of Satellites Required-Algebra Problem-Algebra Problem

Unknown time

latitudelongitudeelevation

4 4 Unknowns We Need 4 Satellites

Equation satellite location

Minimum # of Satellites RequiredMinimum # of Satellites Required-Trilateration-Trilateration

1 satellite – somewhere on a sphere

Minimum # of Satellites RequiredMinimum # of Satellites Required-Trilateration-Trilateration

2 satellites – somewhere on a circle

Minimum # of Satellites RequiredMinimum # of Satellites Required-Trilateration-Trilateration

3 satellites – one of two points

Minimum # of Satellites RequiredMinimum # of Satellites Required-Trilateration-Trilateration

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.

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.

4 satellites – one point3D GPS Location

When There are Only 3 SatellitesWhen There are Only 3 Satellites

• 2D GPS Location

• Elevation - last known

• 2-5 X Error Rule

- Want tetrahedron as large as possible- Want index as low as possible

Garmin Estimated AccuracyGarmin Estimated AccuracyRelies on Dilution of Precision

DOPsTDOPVDOPHDOPPDOPGDOP

DOPsTDOPVDOPHDOPPDOPGDOP

Ideal Satellite GeometryIdeal Satellite GeometryIdeal Satellite GeometryIdeal Satellite GeometryN

S

W E

Good Satellite GeometryGood Satellite GeometryGood Satellite GeometryGood Satellite Geometry

Poor Satellite GeometryPoor Satellite GeometryPoor Satellite GeometryPoor Satellite GeometryN

S

W E

Poor Satellite GeometryPoor Satellite GeometryPoor Satellite GeometryPoor Satellite Geometry

Positions Recorded by Positions Recorded by Stationary GPS ReceiverStationary GPS Receiver

Garmin GPSmap76S 1 position/second10 minutesWAAS Disabled

3.6 meters

3.1 meters

ErrorsErrors(tens of meters)(tens of meters)

IonosphereTroposphereSatellite Clock Errors Satellite Ephemeris ErrorsMultipath Receiver Noise

DGPS SiteDGPS Site

xx+30, +30, yy+60+60

xx+5, +5, yy-3-3

True coordinates = True coordinates = xx+0, +0, yy+0 +0

Correction = Correction = xx-5, -5, yy+3+3

DGPS correction =DGPS correction = x x+(30-5) and +(30-5) and yy+(60+3)+(60+3)

True coordinates = True coordinates = xx+25, +25, yy+63+63

xx-5, -5, yy+3+3

Real Time Differential GPSReal Time Differential GPSReal Time Differential GPSReal Time Differential GPS

DGPS ReceiverDGPS ReceiverReceiverReceiver

WAAS satellitesWAAS satellites

GPS GPS ConstellationConstellation

WAAS Control WAAS Control StationStation

(Position known)(Position known)GPS receiverGPS receiver(Position with (Position with errors)errors)

Wide Area Augmentation Wide Area Augmentation SystemSystem

25 Reference Stations 25 Reference Stations (Position known)(Position known)

WAASWAASWide Area Augmentation System

WAAS Satellite

Errors Reduced by Errors Reduced by WAAS CorrectionWAAS Correction

(multi-meter)(multi-meter)IonosphereTroposphereSatellite Clock Errors Satellite Ephemeris ErrorsMultipath Receiver Noise

Receiving WAAS CorrectionReceiving WAAS Correction

If WAAS signal intermittent- WAAS correction for SV 19

No WAAS correction for SV 11

WAAS correction for SV 19No WAAS correction for SV 11

Caution!Caution!If WAAS Enabled –

- 2D WAAS chosen over 3D uncorrected- WAAS chosen over DOP

RecommendationRecommendationIf WAAS signal intermittent

(example: under canopy) - disable WAAS

Signal DisruptionSignal DisruptionSignal DisruptionSignal Disruption

Ionosphere

Solid Structures

Metal Electro-magnetic Fields

Good Data Collection TechniquesGood Data Collection Techniques

External AntennaMap76S more accurate under canopy

Sleeve Mounts

Vehicle Brackets

Map Projections & Map Projections & Coordinate SystemsCoordinate SystemsMap Projections & Map Projections &

Coordinate SystemsCoordinate Systems

Projecting a Sphere Onto a Projecting a Sphere Onto a PlanePlane

Projecting a Sphere Onto a Projecting a Sphere Onto a PlanePlane

Three-dimensional sphere to two-dimensional flat map.Three-dimensional sphere to two-dimensional flat map.

Examples of Several Examples of Several ProjectionsProjections

Examples of Several Examples of Several ProjectionsProjections

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

Coordinate Systems Coordinate Systems (Projections)(Projections)

We Use – 2 Coordinate Systems

Latitude / LongitudeUniversal Transverse Mercator (UTM)

Garmin -

29 Location Formats

0º0º

0º0º

PointPoint ofof OriginOrigin

PrimePrime MeridianMeridian

EquatorEquator

(Longitude)(Longitude)

(Latitude)(Latitude)

10º N10º N

30º N30º N

10º S

Latitude & LongitudeLatitude & LongitudeLatitude & LongitudeLatitude & Longitude

ParallelsParallels ofof LatitudeLatitudeParallelsParallels ofof LatitudeLatitude

10º10º

10º10º

10º10º

690690 milesmiles

690690 milesmiles

690 miles690 miles

10º S10º S

0º N0º N

10º N10º N

20º N20º N

Meridians of LongitudeMeridians of LongitudeMeridians of LongitudeMeridians of Longitude

10º10º

10º10º

110º W110º W120º W120º W

690 miles690 miles

460 miles460 miles

240 mi240 mi10º10º

Equator

To North Pole

To South Pole

Three Ways To Express Three Ways To Express Latitude / LongitudeLatitude / Longitude

on a Garminon a Garmin

Three Ways To Express Three Ways To Express Latitude / LongitudeLatitude / Longitude

(for (for the Samethe Same Location) Location)

hddd° mm’ ss.s”Degrees-Minutes-Seconds (Decimal Seconds)N 43° 40’ 55.8”, W 116° 17’ 14.1”

hddd° mm.mmm’Degrees-Minutes (Decimal Minutes)N 43° 40.930’, W 116° 17.235’

hddd.ddddd°Degrees (Decimal Degrees)N 43.68216°, W 116.28725°

Coordinate SystemsCoordinate SystemsCoordinate SystemsCoordinate Systems

hddd0 mm’ ss.s”: N 430 40’ 55.8” X W 1160 17’ 14.1”

(55.8” / 60 = .93’)

Different coordinates representing the same location:

hddd0 mm.mmm’: N 430 40.93’ X W 1160 17.235’(40.93’ / 60 = .682160)

hddd.ddddd0 : N 43.682160 X W 116.287250

UTM/UPS: 11T 0557442m E 4836621m N

Example: Error in LatitudeExample: Error in Latitude

35° 24´ 45˝ N

35° 24.450’ N

1/3 of a mile

Lat / Long ShortcomingsLat / Long Shortcomings

1 minute??

??

1 d

eg

ree

1 1 degree

+

+

+

??

Universal Transverse MercatorUniversal Transverse Mercator

• measured in meters• located in zones (1 - 60)• include northing and easting• are positive

Coordinates

Zone Easting

Northing

Latitude Band

UTM Zones in the Lower 48 UTM Zones in the Lower 48 UTM Zones in the Lower 48 UTM Zones in the Lower 48

10101111

12121313

1414 1515 1616 17171818

1919

UTM ZonesUTM Zones

1 60

UTM Grid OverlayUTM Grid OverlayUTM Grid OverlayUTM Grid Overlay60 Zones, and 20 Latitude Bands

21

G

M

WX

80º S

84º N

D

C

EF

HJ

KL

NP

QRST

UV

Lat

itu

de

Ban

ds

21 T

T

Zones

Equator

Garmin Uses – UTM bands

Bands C - M, southern hemisphereBands N - X, northern hemisphere

UTM Latitude BandUTM Latitude Band

Latitude Band

We Use – 2 GIS choices

UTM Zone _ NorthUTM Zone _ South

no “I”no “O”

no “I”no “O”

If You Don’t Know Zone, If You Don’t Know Zone, Latitude Band… Latitude Band…

Entering WaypointsZone – look upBand – enter any letter C – M for

northern hemisphere, receiver will display correct one

Collecting WaypointsReceiver figures it out!

UTM Location FormatUTM Location Format on a Garmin on a Garmin

What is a datum?What is a datum?

DatumsDatums

WGS 84 NAD 83 NAD 27

Garmin -

>100 Map Datums

We Use –

3 Datums

1 meter1 meter 10 - 120 meters10 - 120 meters

Example: Datum Shift in ArizonaExample: Datum Shift in Arizona

NAD83NAD83N34.555N34.555oo, W111.195, W111.195oo

NAD27NAD27N34.555N34.555oo, W111.195, W111.195oo

210 meters210 meters

With a Garmin GPS With a Garmin GPS Receiver you Receiver you alwaysalways collect in the collect in the right right coordinate system coordinate system and datum!and datum!

Lat, LongWGS-84

UTC

Lat, LongWGS-84

UTC

Lat, LongNAD27-8 GMT

Lat, LongNAD27-8 GMT UTM

NAD83UTC

UTMNAD83

UTC

Lat, LongWGS84-9 GMT

Lat, LongWGS84-9 GMTLat, Long

NAD27-8 GMT

Lat, LongNAD27-8 GMT UTM

NAD83GMT

UTMNAD83GMT

Lat, LongWGS84

UTC

Lat, LongWGS84

UTC

Display doesn’t matter

Coordinate System?Datum?

Coordinate System?Datum?

Review of TopicsReview of Topics

- GPS- GPS

- WAAS- WAAS

- Coordinate Systems- Coordinate Systems

- Datums- Datums