Introduction to the Global Positioning

System

byDr. Stephen C. Brown

University of Alaska at FairbanksMat Su /Copper River District

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 any where on earth

GPS Is An Excellent Mapping GPS Is An Excellent Mapping ToolTool

–Instantly gives:• Altitude

• Speed

• Longitude and Latitude

Space Segment

•USER SEGMENTLAND SEA AIR

NEEDFour SV’s.

• Maintained by the Department of Defense

Control Segment

How It Works….

TrilaterationTrilateration

How It Works….

How It Works….

How It Works….

How It Works….

Increasing Accuracy:Wide Area Augmentation

Service (WAAS)

100 m 15 m <3m

Recognizing Coordinate Systems

Format Type Example Coordinate (all are same position)

Degrees, Minutes, Seconds (DMS): 290 34’ 15” Decimal Minutes (DM): 290 34.25’Decimal Degrees (DD): 29.57080

290 34’ 15” is the same as 29 34 15290 34.25’ is the same as 29 34.25

Universal Transverse Mercator (UTM) Coordinates

A “metric” coordinate system

5V 605913.13 E6707279.66 N

605913.13 meters Easting

6707

279.

66 m

eter

s N

orth

ing

UTM Zones

The Right Datum is Important!

GPS data stored in WGS84/NAD83 datum and displaying them with GIS data in NAD27 datum can result in 100's of meters in error!

Error Problems in AlaskaSV’s are on an southern equatorial plane

Mountains often block the sky

Extreme cold impact batteries

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

Garmin GPS ReceiversGarmin GPS Receivers

• Inexpensive and downloadable

• Available locally for lessthan $150

• Most GPS receivers similarin operation

SV VisibilitySV Visibility

clear view obstructed view

clear viewclear view obstructed view obstructed view

SkyView PageSkyView Page

• Satellite status appears while the

unit “finds” thesatellites

• Acquisition can take several minutes

WaypointsWaypoints

tracktrack

waypoint 1waypoint 1

2233

44

Creating WaypointsCreating Waypoints

Creating WaypointsCreating Waypoints

Selecting WaypointsSelecting Waypoints

Selecting WaypointsSelecting Waypoints

Selecting WaypointsSelecting Waypoints

What is Geocaching?What is 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

www.easygps.com

GPS Online Resources

www.garmin.com

www.trimble.com

www.geocaching.com

www.earth.google.com

Steve Brown:

ffscb2@uaf.edu

907-745-3639

Mat-Su/Copper River District

University of Alaska Fairbanks

Cooperative Extension Service