Introduction to the Global Positioning

System

bybyDr. Stephen C. BrownDr. Stephen C. Brown

K-State Research and ExtensionK-State Research and ExtensionBrown CountyBrown County

And And Mandy KernMandy Kern

Hiawatha High Agriculture EducatorHiawatha High Agriculture Educator

WHAT IS GPS?

• Satellite based radio positioning system

• Developed and maintained by the U.S. Department of Defense

• Made up of three segments:SpaceControlUser or Ground receivers

• Used for obtaining accurate locations anywhere on earth

Space Segment

GPS Is An Excellent GPS Is An Excellent Mapping ToolMapping Tool

Instantly gives:Instantly gives:AltitudeAltitude

SpeedSpeed

Longitude and LatitudeLongitude and Latitude

How It Works….How It Works….

TrilaterationTrilateration

Math ConnectionMath ConnectionStep 1Step 1

•Suppose we measure our distance from a satellite and find it to be 11,000 miles. •Knowing that we're 11,000 miles from a particular satellite narrows down all the possible locations we could be in the whole universe to the surface of a sphere that is centered on this satellite and has a radius of 11,000 miles.

Math ConnectionMath ConnectionStep 2Step 2

•Next, say we measure our distance to a second satellite and find out that it's 12,000 miles away.• That tells us that we're not only on the first sphere but we're also on a sphere that's 12,000 miles from the second satellite. Or in other words, we're somewhere on the circle where these two spheres intersect.

Math ConnectionMath ConnectionStep 3Step 3

•If we then make a measurement from a third satellite and find that we're 13,000 miles from that one, that narrows our position down even further to the two points where the 13,000 mile sphere cuts through the intersection of the first two spheres.

•So by ranging from three satellites we can narrow our position to just two points in space.

•To decide which one is our true location we could make a fourth measurement. But usually one of the two points is a ridiculous answer (either too far from Earth or moving at an impossible velocity) and can be rejected without a measurement.

•USER SEGMENTLAND SEA AIR

NEEDTHREE SV’s.

• Maintained by the Department of Defense

Control Segment

Sources of ErrorSources of Error Selective Availability (SA Error)Selective Availability (SA Error) AtmosphericAtmospheric SV EphemerisSV Ephemeris

MultipathingMultipathing Poor SV GeometryPoor SV Geometry

EPEEPE (Estimated Position Error) (Estimated Position Error)

The higher the EPE, the greater the Positioning error!

Good EPE’s range from 10-20 feet.

Proper pre-mission planning prevents poor positioning!

Shape of the EarthShape of the Earth(datum)(datum)

PRACTICAL APPLICATIONS

•Navigation•Sailing, hiking and aviation•Collecting and locating way-points

•Locating Features• Stocking locations or stream surveys• Endangered or sensitive species locations • Locating trails or physical structures

•GIS•Collecting GPS data along with attribute data• Mapping and database update

•Surveying•Locating Control Points quickly

LOW END UNITS

•Capabilities•20 ft accuracy•1-12 channel receiver•Collect only way point data

•Cost•$80 - $600

•Limitations•Poor reception under tree canopy•No file collection

•Applications•Navigation for hiking or sailing

•Capabilities• Sub-meter accuracy with DGPS• 6-12 channel receiver• Collects static, mobile and attribute data

•Cost• $2,500 - $15,000

•Limitations•Not accurate for surveying

•Applications• Navigation • Mapping•GIS Update

MID-RANGE UNITS

•Capabilities• cm accuracy with DGPS• 12 channel receiver• Collects static points

•Cost• $15,000 - $100,000

•Applications• Surveying

HIGH END UNITS

Garmin GPS ReceiversGarmin GPS ReceiversGarmin GPS ReceiversGarmin GPS Receivers

Inexpensive and downloadableInexpensive and downloadable

Available locally for lessAvailable locally for lessthan $150than $150

Most GPS receivers similarMost GPS receivers similarin operationin operation

Okay, lets see how it Okay, lets see how it works!works!

Okay, lets see how it Okay, lets see how it works!works!

Page Button

PowerButton

Zoom out/inButton

FindButton

Thumbstick

Pages In the GPS UnitPages In the GPS UnitPages In the GPS UnitPages In the GPS Unit

SV VisibilitySV VisibilitySV VisibilitySV Visibility

clear viewclear view obstructed viewobstructed view

clear viewclear view obstructed view obstructed view

Satellite StatusSatellite Status Page PageSatellite StatusSatellite Status Page Page

Satellite status Satellite status appears while appears while the unit “finds” the unit “finds” the satellitesthe satellites

Acquisition can Acquisition can take several take several minutesminutes

Satellite StatusSatellite Status Page PageSatellite StatusSatellite Status Page Page

Satellite elevation/position

Signal strength

Receiver position

Main PageMain PageMain PageMain Page

The main page The main page allows user to edit allows user to edit waypoints, tracks waypoints, tracks and routes or and routes or configure system configure system to personal to personal preferencepreference

Map PageMap PageMap PageMap Page

Allows you to Allows you to view map of view map of current location, current location, waypointswaypoints and and trackstracks

WaypointsWaypoints

tracktrack

waypoint 1waypoint 1

2233

44

Creating Creating WaypointsWaypointsCreating Creating

WaypointsWaypoints Marking waypoints Marking waypoints

allows you to allows you to remember and return remember and return to a specific locationto a specific location

Waypoints are created Waypoints are created by pressing and by pressing and holding thumbstickholding thumbstick

Finding WaypointsFinding WaypointsFinding WaypointsFinding Waypoints Pressing “Find” Pressing “Find”

button will bring up a button will bring up a list oflist of waypointswaypoints

Entering a waypoint Entering a waypoint will result in “as the will result in “as the crow flies” directions crow flies” directions to that pointto that point

Finding WaypointsFinding WaypointsFinding WaypointsFinding Waypoints

Name of Waypoint

Distance to Waypoint

Bearing to Waypoint

Heading

Speed

What is What is Geocaching?Geocaching?

What is What is Geocaching?Geocaching?

Geocaching is a worldwide “scavenger hunt” using GPS to find “caches” of treasure. The only rules are to leave something if you take

something and do not disturb the cache

Links to using GPS into the Links to using GPS into the ClassroomClassroom

http://worldofagriculture.org/WOA-prhttp://worldofagriculture.org/WOA-precag.htmecag.htm

Let’s Practice!!Let’s Practice!!

Waypoint #1 – N 39Waypoint #1 – N 39°51.102°51.102

W 095W 095°31.536°31.536 Waypoint #2 – N 39Waypoint #2 – N 39°51.081°51.081

W 095W 095°31.590°31.590 Waypoint #3 – N 39Waypoint #3 – N 39°51.113°51.113

W 095W 095°31.417°31.417 Waypoint #4 – N 39Waypoint #4 – N 39°51.090°51.090

W 095W 095°31.400°31.400