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:
907-745-3639
Mat-Su/Copper River District
University of Alaska Fairbanks
Cooperative Extension Service
