Introduction to Global Positioning Systems GPS for UCCE

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Introduction to Global Positioning Systems (GPS)
for UCCE

• August 21, 2007
• Karin Tuxen-Bettman
• GIIF
• Maggi Kelly
• Department of Environmental Science, Policy, and
  Management
• http//giif.cnr.berkeley.edu

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Geospatial Informatics
Remote Sensing
GIS
Internet
Spatial Analysis
Supporting research management
in the natural social sciences.
GPS
Visualization
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GIIF Services
Training Workshops
Support Consulting
Map Poster Printing
Data Database Services
WebGIS Services
GPS Rental
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This Mornings Outline

• GPS theory, or What is GPS?
• Sources of error in GPS and improving your
  accuracy
• GPS standardization
• Position Format (i.e. Projection)
• Map Datum
• Navigating and collecting waypoints
• Field exercise upload/download points from a
  computer into a GPS unit. Then we will go
  outside where youll navigate to and collect
  points, and overlay your points on base data
  (using ArcMap, Google Earth, and QGIS)

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What is GPS?Global Positioning Systems

• 24 active satellites make up civilian GPS
• 6-7 satellites are visible from any spot on Earth
• 6 orbit planes, each with 4 operational
  satellites
• Orbiting 12,000 miles above earth at 7,000 mph
• 2 complete orbits in less than 24 hours

• 4 or more GPS satellites used to compute X, Y,
  and Z

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Brief History

• Officially named NAVSTAR GPS (Navigation Signal
  Timing and Ranging GPS)
• GPS satellites began being launched in 1978, and
  was completed in March 1994.
• Developed by the US Dept. of Defense to provide
  navigation capabilities for military forces.
• Managed by the Schriever Air Force Base costs
  approx. 400 mil/year (maintenance, replacement
  of aging satellites, etc.), but GPS is available
  for free use in civilian applications as a public
  good.

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Why GPS?

• Accurately determine their location (X,Y,Z) in
  any weather, day or night, anywhere on Earth.
• Integral to numerous civilian applications and
  industries around the globe
• recreational uses (e.g. boating, aircraft,
  hiking)
• corporate vehicle fleet tracking
• surveying (including research, management, etc.)

TomTom
OnStar
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How GPS Works

• Need 4 or more satellites for accurate location!

Good tutorialshttp//www.trimble.com/gpshttp//
oceanservice.noaa.gov/education/kits/geodesy
Image credit NOAA
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How GPS Works

• GPS satellites transmit two low power radio
  signals, designated L1 and L2
• Both signals travel by line of sight
• Will pass through clouds, glass, plastic
• Will not go through most solid objects, such as
  buildings mountains

L1
L1
L1
L1
L2
Image credit adapted from www.dgps.it
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GPS Accuracy

• Accuracy primarily depends on
• Number of satellites used to calculate position
• Strength of the signal of those satellites
• Satellite position/geometry
• Positional Dilution of Precision (PDOP)
• Geometric Dilution of Precision (GDOP)
• Horizontal Dilution of Precision (HDOP)
• Differential Correction Procedures
• WAAS (can improve to 2-5m)
• DGPS (can improve to 0.1-1m)
• (Your GPS unit must be WAAS- or DGPS-compatible!)

Image credit P.H. Dana, Garmin
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What can cause GPS Signal Errors?

• Several factors can degrade GPS signal and affect
  accuracy
• Signal multi-pathThis occurs when the GPS signal
  is reflected off objects such as tall buildings
  or large rock surfaces before it reaches the
  receiver. This increases the travel time of the
  signal, thereby causing errors.
• Ionosphere and troposphere delaysThe satellite
  signal slows as it passes through the atmosphere.
  The GPS system uses a built-in model that
  calculates an average amount of delay to
  partially correct for this type of error. Any
  error due to this is usually negligible.
• Receiver clock errorsA GPS receiver's built-in
  clock is not as accurate as the atomic clocks
  onboard the GPS satellites. Leads to slight
  timing errors. Any error due to this is usually
  negligible.
• Orbital errorsAKA ephemeris errors, these are
  inaccuracies of the satellite's reported
  location. Any error due to this is usually
  negligible.
• Intentional degradation of the satellite
  signalSelective Availability (SA) is an
  intentional degradation of the signal once
  imposed by the U.S. Department of Defense turned
  off SA in May 2000.

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Increasing your accuracy

• Wide-Area Augmentation System (WAAS)
• Can improve accuracy of GPS signals to within 2
  meters (6 ft) for compatible receivers.
• Differential GPS (DGPS)
• Can improve accuracy to about 1 cm (½ inch).
• L2C
• Will increase the accuracy of your L2 signal
• The first in a series of next-generation GPS
  satellites was launched in late 2005.
• Offers a second civilian GPS signal called L2C
  for enhanced accuracy and reliability.

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Wide Area Augmentation System (WAAS)

• 25 ground reference stations positioned across
  the U.S.
• Send data to 2 master stations
• 2 master stations (on west and east coasts)
• Accounts for satellite orbit, clock drift, and
  signal delays
• Sends corrections to geo-synchronous equatorial
  satellites, which is received by your GPS unit

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Wide Area Augmentation System (WAAS)

• Can improve accuracy to within 2 meters
• but need unobstructed view of the horizon!
• Only available in North America
• Ideal for open land and marine applications
• Recommendation Purchase a WAAS-compatible GPS
  unit!

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Differential GPS (DGPS)

• Real-time DGPS
• Incorporates the L2 satellite signal real-time
• Need special DGPS equipment

• Post-processed DGPS
• Get data from Continuously Operating Reference
  Stations (CORS) network
• Designed to meet post-processing needs of GPS
  users
• Works with the GPS data you collected out in the
  field, and adds

Image credit NLWRA
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GPS Standardization

• Position Format
• How 3-D earth is mapped on a2-D surface
• Same thing as projection
• Map Datum
• Mathematical model that fits the earth to an
  ellipsoid
• Most important thing is to be consistent and
  document what you do!

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GPS Standardization Position Format

• All handheld units allow you to chose between
• UTM/UPS and Lat/Long (Geographic)
• Use Universal Transverse Mercator (UTM/UPS)
• Avoid using geographic coordinates (latitude,
  longitude)
• 1 latitude 1 longitude
• This is not the case on the earth

Increasing distortion of shape, area, distance,
and Scale.
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GPS Standardization Position Format

• Avoid using latitude and longitude (degrees,
  minutes, seconds)
• Some units collect in Degrees, Minutes, Seconds
• 38 40 15
• Some in Decimal Degrees
• 38.6691
• Some in Degrees, Decimal Minutes
• 38 40.25
• By misinterpreting these, you can introduce
  substantial error.
• For example

38 40.25 ? 38 40 25 ? 38 40.4166 ? ? 234 m
If someonewrites this
And you thinkits this
But its really this!
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GPS Standardization Position Format

• Avoid using latitude and longitude (degrees,
  minutes, seconds)
• Rounding can introduce error
• 38.6691 ? 7.9 m
• 38.669 ? 79.0 m
• 38.67 ? 790.5 m
• 38.7 ? 7904.8 m
• By rounding the latitude and longitude, you can
  introduce substantial error.

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GPS Standardization Position Format

• UTM coordinates are a better option
• (Easting, Northing) (X,Y)
• Expressed in meters
• Northings (e.g. 4286289) and Eastings (e.g.
  0525690)
• Each integer equals 1 meter
• Easting (walk 1m east, 0525690 ? 0525691)
• North (walk 1m north, 4286289 ? 4286290)
• Easy to understand your movement in field

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GPS Standardization Map Datum

• Most common map datums
• WGS84 (World Geodetic Survey, 1984)
• NAD83 (North American Datum, 1983)
• NAD27 (North American Datum, 1927)
• USGS Topo maps are NAD27
• Use whatever is appropriate for your area.
• WGS84 if you are going to compare with GPS data
  you have collected elsewhere in the world.
• NAD83 if you are in N. America, and are
  collecting raw data
• NAD27 if you are in N. America, and want to
  match your NAD27 topo maps
• Most GPS are set to WGS84 out-of-the-box (same as
  NAD83)

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Horizontal Datum Shift

• BEWARE of the Datum Shift!
• You can easily transform between datum.
• Datum shift in California NAD27 vs. NAD83
• 100 m east
• 200 m north
• The industry standard for converting between
  datums is called NADCON
• Do this in ArcGIS software!

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Horizontal Datum Shift
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Types of GPS Units
Recreational-grade
Mapping-grade
Survey-grade
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GPS Options for Field Research

• Garmin w/ field notes
• Handheld GPS
• Field notebook
• PROS
• Simple, light-weight, and inexpensive
• CONS
• Only gives GPS coordinates
• Restricted to lower accuracy (2-15 m error)

• Field PDA system
• PDA
• GPS
• Software
• PROS
• Collects data electronically
• Uses custom programs and forms
• Overlay GPS points on imagery in the field
• Improved accuracy (up to 10 cm)
• CONS
• Expensive
• Sometimes NOT user-friendly
• Less light-weight

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Handheld GPS Units

• Accuracy is usually 5-15m can be as much as 50m
  due under heavy canopy, PDOP, etc.
• Cannot set PDOP threshold
• Some have WAAS differential correction to improve
  accuracy to 2-5m.

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Guide to the Handheld Garmin models

• C Color display
• S Electronic compass and barometric altimeter
• X Expandable memory, new SiRF chip

Garmin GPSmap 60 CSx
Garmin eTrex Vista Cx
Garmin GPSmap 76 C
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Field PDAGPS units
Rugged
Integrated GPS
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Field PDAGPSWhat You Need

• PDA
• GPS (if needed)
• Software

GPS Pathfinder Office
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What unit is right for you?

• What are your accuracy needs?
• 2-15 m handheld units are okay
• lt2 m mapping-grade units are needed
• GPS good for mapping points, lines, and polygons
  of relatively small areas
• Very large areas should be mapped/digitized using
  imagery in a GIS.
• How much data will you collect?
• Points, lines, AND polygons?
• Extensive field note taking?

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Plot Field Samples
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Tracking Movement
Tracking whales
Hourly Daily
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GPS Activities

• GPS scavenger/treasure hunt
• http//www.geocaching.com/

GPS Drawing http//www.gpsdrawing.com/
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GPS Field Exercise The ESPM Tree Trail

• We will be using the ESPM tree
• trail to navigate to existing
• waypoints, and collecting new
• ones.

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GPS Field Exercise

• Get comfortable with the GPS unit,
• Upload points to the GPS unit,
• Navigate to the existing tree trail points in
  the field,
• Collect new points in the field, and
• Download new points to the computer to use with
  your GIS projects.

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Using your GPS unit

• 1. Turn power on

eTrex Vista
eTrex Vista C
GPSmap 60
GPSmap 76
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Using your GPS unit

• 2. Move between pages

eTrex Vista
eTrex Vista C
GPSmap 60
GPSmap 76
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Satellites Page
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Compass Page
Dont forget to calibrate your compass at the
start of every field day!
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Map Page
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Menus
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Using your GPS unit

• 3. Zoom in on the map

eTrex Vista
eTrex Vista C
GPSmap 60
GPSmap 76
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Using your GPS unit

• 4. Find a waypoint

eTrex Vista
eTrex Vista C
GPSmap 60
GPSmap 76
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Using your GPS unit

• 4. Find a waypoint and navigating to it!

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Using your GPS unit

• 5. Collecting a new waypoint, or marking

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Using your GPS unit

• 5. Collecting a new line, or track

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Transferring your GPS points

• Garmins Trip Waypoint Manager
• GPS Toolbar in ArcMap (serial cable only!)
• GPS Babel (Google Earth QGIS use this)
• Google Earth Plus Pro

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Connecting your GPS unit
eTrex Vista
eTrex Vista C
GPSmap 60
GPSmap 76