An Introduction to GPS. Prepared by:. John McGee Jennifer McKee. With support from:. NSF DUE-0903270. in partnership with:. Geospatial Technician Education Through Virginia’s Community Colleges (GTEVCC). Outline. Why do we use GPS? What is GPS? How does GPS Work?
With support from:
in partnership with:
Geospatial Technician Education Through Virginia’s Community Colleges (GTEVCC)
332 Elm St.
Frog Holler, VA
Location, Location, Location
And how does it work?
There are three major components in this system:
stations that monitor the satellites.
If the GPS receiver only obtains signals
from 1 Satellite, then it “knows” that it
is located somewhere on this sphere…
If the GPS receiver only obtains signals from 2
satellites, then it “knows” that it is located
somewhere where these 2 spheres intersect
If the GPS receiver obtains signals from 3 satellites, then it “knows” that it is located somewhere where these 3 spheres intersect (2 points)
A fourth satellite is required to determine the exact location and elevation.
There are 2 types of GPS Signals:
P-code: (“Precise” code)
C-code: (“Civilian” Code).
Never say never…. But SA may not be “turned on” again….
300 feet is a lot of real estate!!!Selective Availability
The GPS tells you
that you are located
But your real
location is here…
Base station w/ GPS
receiver at known location:
GPS receiver in the field
collecting points, routes, etc.
Exact known (surveyed) coordinates differ from GPS coordinates at this location = exact amount of error!
Most (but not all) GPS receivers are WAAS compatible.
95% of GPS receivers on the market today are WAAS compatible
The GARMIN Venture HC is WAAS compatible
GPS Collected Points
GPS Averaged Position
Satellites may not be visible…
This can introduce error…Other Tricks of the Trade: MultiPath Errors
GPS has worldwide coverage…
You can lose satellite coverage (or received degraded signals) in areas with dense foliage, in “urban canyons”, etc.
You may also lose satellite coverage (or receive degraded signals) in deep valleys or gorges.
Acknowledgements: Dr. Phillip Rasmussen, Utah Geospatial Extension Specialist
Brand “A” Day 2
Brand “A” Day 3
Brand “A” Day 4
Brand “A” Day 5
Brand “B” Day 1
Brand “B” Day 2
Brand “B” Day 3
Brand “B” Day 4
Brand “B” Day 5
These are called WayPoints.
Field corners, insect infestation areas, crop damage, individual trees, trail heads, creek crossings, point source pollution, camping sites, and don’t forget “your car”!
Longitude: W80° 28’ 45”
Elevation: 2108 feet
Date: 05/08/2009Tracks (just start walking…)
* We’ll do this later!
Yellow lines = Route
Red lines = Track
Red dots = Track points
Using the ‘GOTO’ function, the GPS will guide you to a predefined Waypoint (you choose which one…) using an electronic compass and “pointer”
You can program the GPS to “beep” when you are within a certain distance of a selected Waypoint
GPS’s calculate your ground speed as you walk, run, drive, or fly
In addition to providing you with your latitude and longitude, GPS provides you with elevation information. Elevation is not as accurate as X,Y information.
Some GPS’s have built in barometric altimeters (to increase accuracy of z values). This option costs a bit extra!
-better coverage availability (i.e. in forested areas)
-anticipated greater accuracy (even for the recreational grade GPS receivers)
Europeans, Chinese, India, etc.
Check out the specs.! High sensitive receivers are worth the extra $
…and keep in mind that there are ~286,000,000 wireless subscribers in the U.S.
You’ve seen those trucks going down the highway with the little “round things” on the top...
provides a history..
. How many hours did you spend planning
your trip to Floyd
and Patrick Counties?
More than 4
Mean = 1.0
Median = 0.5
SD = 1.5
Pat. + Floyd Co. GPS Map
There’s a high correlation between the VDOT traffic count map and the GPS tourist surveys…
Take into account existing traffic and tourist visitor patterns
Basically, any profession that
requires data collection “in the field” can benefit from using GPS.
The applications are limited only to your imagination...
And evidence of this can be found on the GPS based applications developed for SmartPhone devices)
Virginia Geospatial Extension Program
John McGee Ph.D.
Geospatial Extension Specialist
Geospatial Project Developer