An Introduction to GPS / GNSS In Partnership with: Prepared by:
NSF DUE-1205110; 0903270
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Outline Terms: GNSS & GPS? Why do we use GNSS? What is
GNSS? How does GNSS Work? What do you need to know about GNSS? What
can you do with GNSS? How is GNSS used in the real world?
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GNSS and GPS GPS = Global positioning system GPS refers to the
constellation of navigation satellites associated with the American
System (which is a global system). For a long time, GPS was the
only game in town, so everything (satellites, receivers, etc.) was
referred to as GPS Times are changing other options (besides GPS)
are quickly developing
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GNSS = Global Navigation Satellite System GNSS is an umbrella
term that includes any satellite navigation system. Options
include: GPS (U.S. | operational since 1994) GLONASS (Russian |
re-operational since 2010) Galileo (European Union | anticipated
operation:2019) Compass (China | Operational in Asia/Pacific since
2012 / anticipated global operation: 2020)
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Why GNSS? Many features have addresses and landmarks that are
associated with a destination. Fred Jones 332 Elm St. Frog Holler,
VA 42534
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Why GNSS? However, there are many features that do not have
addresses There are many MAJOR cities that do not even have STREET
NAMES! And then there is the open ocean and sky
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Why GNSS? Location, Location, Location and INFORMATION!!!
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Pre-GPS Navigation is critical Historical Navigational tools
have limits: The Sextant doesnt work if it is cloudy Lowrance
radionavigation: only worked near land The military had its own
reasons for determining location Identify targets Friendly fire
issues smart bombs
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What is GNSS And how does it work?
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What is GPS? GPS (and GNSS) is not a single UNIT! GPS = Global
Positioning SYSTEM GPS was developed by the Department of Defense
at a cost of >$12 billion Funding for the GPS was contingent on
making the system available to the public.
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GPS (and GNSS) is a SYSTEM There are three major components in
this system: 1.Satellites 2.Ground Control Stations 3.GNSS
Receivers (or units)
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Satellites There are 24-32 satellites up there at any given
time orbiting the earth at ~11,000 naut. miles. The DOD knows the
EXACT location of each of the satellites at any given moment. These
satellites have VERY accurate clocks on board. The satellites
continuously send radio signals towards earth. These radio signals
are picked up by GPS receivers.
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Satellites: A Beehive of Activity
http://www.nasa.gov/multimedia/imagegallery/image_feature_1283.html
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Control stations enable information on Earth to be transmitted
to the satellites (updates and fine turning). Control stations
continuously track satellites, and update the positions of each
satellite. Without control stations, the accuracy of the system
would degrade in a matter of days. GPS Control Stations There are
five control stations that monitor the satellites.
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GPS Receivers GPS units are referred to as receivers. They
receive information (radio signals) from satellites. The GPS
receiver knows how long it takes the signal to travel from the
satellite to the receiver.
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GPS Receivers The GPS receiver knows how long it takes the
signal to travel from the satellite to the receiver. The Receiver
is therefore able to calculate its distance from the satellite.
Distance = time x velocity Distance = time x 186,355 mi./sec. The
receiver can calculate the time that signal traveled from the
satellite to the receiver. The receiver is therefore able to
determine its exact distance from the satellite.
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How GPS (and GNSS) Works One satellite
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How GPS Works If the GPS receiver only obtains signals from 1
Satellite, then it knows that it is located somewhere on this
sphere
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How GPS Works
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If the GPS receiver only obtains signals from 2 satellites,
then it knows that it is located somewhere where these 2 spheres
intersect
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How GPS Works
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If the GPS receiver obtains signals from 3 satellites, then it
knows that it is located somewhere where these 3 spheres intersect
(2 points)
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How GPS Works
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A fourth satellite is required to determine the exact location
and elevation. How GPS Works
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What do you need to know about GNSS?
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Different Grades of GNSS receivers Recreational Grade GNSS
Accurate to within 5 meters (could be better, but dont rely on it)
Suitable for hunting, recreational, and some business uses Lowest
cost (smallest, and easiest to use): ~$100-$800 Mapping Grade GNSS
Accurate to within 1 meter (3 feet) Requires differential
processing (from a base station) Suitable for many natural resource
applications, city planning $800-$7,000 Survey Grade GNSS Accurate
to within 1 cm Suitable for building bridges $15,000 -$30,000
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What you need to know about GNSS? Signal Accuracy Issues
Selective Availability Tricks of the Trade Current Applications of
GNSS Future applications of GNSS
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GPS: Signal Accuracy There are 2 types of GPS Signals: P-code:
(Precise code) This is only available to the military and some
selected public officials. Very precise, not degraded. C-code:
(Civilian Code). Less precise Signal can be degraded (by scrambling
the signal) especially in times of conflict. This is what the
GARMIN receivers (and all public GPS receivers) work with
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Correcting for errors: Selective Availability It is possible to
correct for inherent signal errors. This process is called
Differential Correction Heres how it works
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Differential Correction There are already established base
stations established around the U.S. Surveyors have determined the
precise location of these base stations. Each base station has a
GNSS receiver, which collects incoming (error prone) signals. The
true (surveyed) location coordinates are then compared to the GNSS
coordinates. The correction values are then: Posted to the web for
later correction (post-processing); sent to other GNSS receivers in
the field (correction on the fly).
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Differential Correction Exact known (surveyed) coordinates
differ from GNSS coordinates at this location = exact amount of
error! GNSS receiver in the field collecting points, routes, etc.
Differential Correction Signal Base station w/ GNSS receiver at
known location:
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WAAS The Wide Area Augmentation System (WAAS) is a differential
GNSS system that is being constructed to support GNSS accuracy in
aircraft. WAAS also provides additional accuracy on the ground The
GNSS receivers that we are using are WAAS compatible
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WAAS Most (but not all) GNSS receivers are WAAS compatible. 95%
of GNSS receivers on the market today are WAAS compatible The
GARMIN Venture HC is WAAS compatible
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Other Tricks of the Trade: Averaging Averaging: A GNSS receiver
can collect points continuously for 15-30 seconds. The receiver can
then average all these locations together This only works when you
are standing still!! Note that not all GNSS receivers have an
averaging capability GNSS Collected Points GNSS Averaged Position
True location
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Other Tricks of the Trade: Satellite Distribution It is better
for your receiver to get a fix on distributed satellites, then
poorly distributed satellites. Poor Satellite Distribution Good
Satellite Distribution Positional Dilution of Precision
GNSS Satellite Visibility: Blacksburg July 12, 2012
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Other Tricks of the Trade: MultiPath Errors Try and stay away
from buildings and other structures when using a GNSS receiver
Satellites may not be visible This can introduce error
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Other Tricks of the Trade: Tracking Satellites GNSS has
worldwide coverage HOWEVER 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.
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Accuracy How accurate is a $150 GNSS? Thats the million dollar
question
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How accurate is a $150 GNSS? (It depends) Acknowledgements: Dr.
Phillip Rasmussen, Utah Geospatial Extension Specialist
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Brand A Day 1 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
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GNSS Data Collection Waypoints Tracks Routes Find/GOTO And
more..!
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What can you do with a GNSS? Collect and store points
(positions) These are called WayPoints. Field corners, insect
infestation areas, crop damage, individual trees, trail heads,
creek crossings, point source pollution, camping sites, and dont
forget your car! Download the points onto your computer and
integrate them with other mapping programs
What can you do with a GNSS? Collect and store the path that
you have walked / driven These paths are called TRACKS. Calculate
the distance of a track (i.e. perimeter around a field) Calculate
AREA measurements within a TRACK (after walking around a field or
parking lot...) Save and Download TRACKS onto your computer.
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Tracks (just start walking) What
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Tracks (just start walking) Latitude: 37 16 18 Longitude: W80
28 45 Elevation: 2108 feet Time: 13:22.15 Date: 05/08/2009 Each
track point has important information associated with it... Virtual
bread crumbs Track points can be collected: Based on a time period
(every 10 seconds) Based on distance (every 20 feet) Or a
combination of time and distance (every 10 secs. or 20 feet,
whichever comes first).
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Tracks You can track your way back...* You can use the track
data to estimate area / perimeter* You can use the time stamp in
the trackfile to georeference (or geotag) photographs!* * Well do
this later!
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What can you do with a GNSS? Collect and store ROUTES Routes
are similar to TRACKS, but are created by associating a series of
Waypoints Tracks are straight lines... Routes can be handy for
measuring square fields and straight lines You can measure the
length and area (acreage) of a Route.
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Routes 1.Establish Waypoints at strategic locations 2.The GNSS
Receiver Connects the dots 3.Area and perimeter measurements are
generated #4 #2 #5 #3 #1
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Routes vs. Tracks Yellow lines = Route Red lines = Track Red
dots = Track points
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What can you do with a GNSS? Navigation! The GOTO (or Find)
function Using the GOTO function, the GNSS will guide you to a
predefined Waypoint (you choose which one) using an electronic
compass and pointer The GOTO/FIND function is like using Autopilot
You can program the GNSS to beep when you are within a certain
distance of a selected Waypoint
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Tide Tables Many of the marine GNSSs have built in tide tables.
They provide tidal information and ranges for any date and any
place The GARMIN Venture HC does not have tide table information
Extra bell & whistle = extra $! What can you do with a
GNSS?
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Speed GNSSs calculate your ground speed as you walk, run,
drive, or fly What can you do with a GNSS?
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Elevation In addition to providing you with your latitude and
longitude, GNSS provides you with elevation information. Elevation
is not as accurate as X,Y information. Some GNSSs have built in
barometric altimeters (to increase accuracy of z values). This
option costs a bit extra!
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Measure Area / perimeter Farmers can use a GNSS to measure the
area of a pasture or a field of corn Natural Resource Agents can
measure the area of a proposed conservation easement Educators (and
students!) can measure the area of impervious surfaces (or green
space) around their campuss and communities... What can you do with
a GNSS?
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Current Application Areas of GNSS Public Safety Environmental
resource management Aviation Military Local planning Surveying
Recreation Business
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The Future of GNSS (is bright) Acknowledgements: Keith
Clarke
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The Future is bright The DoD is in the process of upgrading the
existing GNSS satellite constellation -better coverage availability
(i.e. in forested areas) -anticipated greater accuracy (even for
the recreational grade GNSS receivers)
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WAAS Satellites Historically, some areas in Virginia have had
trouble acquiring the WAAS satellite A new WAAS satellite was
launched in Fall 2006 Better coverage for Virginia = higher
accuracy levels
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The Russian GNSS System Is called GLONASS Has fallen into
disrepair. Some new Russian GLONASS satellites are have been
launched Impacts: Potentially increased accuracy for US receivers
that receive both US and Russian GNSS satellite signals (the
private sector follows demand) Just need to keep our eye on the
Russian economy (no $, no satellites!)
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The European GNSS System Galileo will be Europes own global
navigation satellite system More accurate than the U.S.s current
GNSS system (~4 feet) Better coverage area than the U.S.s current
GNSS system Compatible and interoperable with the American global
positioning system (so weve been told...) Europeans, Chinese,
India, etc.
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GNSS Receivers Continue to get better and better better
antennae, more efficient power consumption, smaller increasingly
more bells + whistles (maps, hard drives, cameras, etc.)
Inexpensive, but the new bells + whistles keeps prices fairly
stable...
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The applications are endless and keep in mind that there are
~322,000,000 wireless subscribers in the U.S. (thats a market
penetration of 101%), as of July 2012. -Source:
http://www.ctia.org
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GNSS recreational (and educational) uses Geocaching. Geocaching
is an entertaining adventure game for GNSS users. The idea is to
hunt for objects (prizes) that have been placed in the landscape
(virtual orienteering). Pick a prize, and leave a prize
http://www.geocaching.com
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but Geocachcing is so pass But have you ever tried
Geodashing?Geodashing In this game, a list of coordinates, selected
at random from around the globe, is presented to all users and
teams. First one there, wins.. Requirements: somebody with a lot of
free time on their hands, a GNSS, Lots of extra batteries, a new
pair of sneakers, a passport, frequent flier miles and your dads
VISA Card (or a trust fund will do).
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Some GNSS Applications are innovative Use GNSS to locate the
loo! http://www.cnn.com/2007/WORLD/europe/11/
29/sat.lav.ap/index.html
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GNSS-based buddy stalkers (oops, I mean buddy tracking) add on
service Create a buddy list and locate your pals on your
Smartphone. Is your girlfriend really at the library?
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Other GNSS Data Loggers and Tracking Devices We all know that
UPS / FedEx and the major freight haulers use GNSS Other folks are
tracking people too!
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Car Navigation Systems are getting into buddy tracking as well
Garmin and TomTom have well established systems in place
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Car Insurance companies have been eyeing this technology for
years
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GNSS-based tracking, routing, and fleet management Youve seen
those trucks going down the highway with the little round things on
the top...
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We are not only tracking trucks... Active tracking: real-time
monitoring... Passive tracking: provides a history..
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Example of passive tracking Rocky Knob Economic Development and
Tourism Study
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Tourist Surveys: Linking GNSS with traditional surveys
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Results 490 visitors contacted over 4 data collection periods
(July, August, September, and October). 323 agreed to participate
(Response rate of 65.9%) Of these 323 visitors, 312 visitors have
returned a survey/GNSS unit (Secondary response rate of 96.6%)
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Tourist surveys Pat. + Floyd Co. GPS Map
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Site Location: Take into account existing traffic and tourist
visitor patterns Theres a high correlation between the VDOT traffic
count map and the GPS tourist surveys
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GPS Fights Crime!
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The Degree Confluence Project The "world's largest distributed
expedition project. Goal: to visit each of the latitude and
longitude integer degree intersections in the world, and to take
pictures at each location.
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GNSS related careers Agriculture Conservation managers Wildlife
technicians Surveying companies Local governments State agencies
Federal agencies The military Law enforcement Real estate Software
programmers Basically, any profession that requires data collection
in the field can benefit from using GNSS. The applications are
limited only to your imagination... And evidence of this can be
found on the GNSS based applications developed for SmartPhone
devices)
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Theres a Variety of Software Products Available to Support GNSS
GPS Utility (free) DNR GPS (free) USA PhotoMaps (free) RoboGeo
(demo version and $75 version) Terrain Navigator (~$89) Data cards
(topos, etc.) and aerial photography subscriptions for your GPS
receiver And just think about all of the 1000s of Smartphone
applications (Urbanspoon, etc.)
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Things to keep in mind... GNSS can serve as an accurate data
collection tool for GIS applications; GPS applications are becoming
increasingly prevalent in our society, and support a variety of
applications; With GNSS receivers, you (more or less) get what you
pay for (w/ prices ranging from $20,000 + - $59); This technology
is CURRENTLY used to support govt. services / private businesses;
Smartphone apps. are going to make all of this take off Knowing how
to use a GNSS does not make you a surveyor!!!