What is GPS

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What is GPS?

• GPS, which stands for Global Positioning System,
  is the only system today able to show you your
  exact position on the Earth anytime, in any
  weather, anywhere.
• The three parts of GPS are
• Satellites
• Receivers
• Software

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GPS Uses

• Police and Emergency Medical Services
• Firefighters  
• Map makers
• Science 

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Satellites

• There are quite a number of satellites out there
  in space. They are used for a wide range of
  purposes satellite TV, cellular phones, military
  purposes and etc. Satellites can also be used by
  GPS receivers.

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GPS Units
Today
1970s
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GPS Satellites

• The GPS Operational Constellation consists of 24
  satellites that orbit the Earth in very precise
  orbits twice a day. GPS satellites emit
  continuous navigation signals.

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DOD

• DOD checks position, altitude and speed
• Relay information to satellite
• Satellite broadcasts information to GPS units

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Speed of Sound

• Count the seconds between the lightning and the
  thunder, then divide by 5.

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GPS Signals

• Each GPS satellite transmits data that indicates
  its location and the current time. All GPS
  satellites synchronize operations so that these
  repeating signals are transmitted at the same
  instant.

Physically the signal is just a complicated
digital code, or in other words, a complicated
sequence of on and off pulses.
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Time Difference

• The GPS receiver compares the time a signal was
  transmitted by a satellite with the time it was
  received. The time difference tells the GPS
  receiver how far away the satellite is.

Satellite transmits at 110000
GPS unit receives at 110005
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Calculating Distance

• Velocity x Time Distance

Radio waves travel at the speed of light, roughly
186,000 miles per second (mps)
If it took 0.06 seconds to receive a signal
transmitted by a satellite floating directly
overhead, use this formula to find your distance
from the satellite.
186,000 mps x 0.06 seconds 11,160 miles
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Triangulation

• Geometric Principle
• You can find one location if you know its
  distance from other, already-known locations.

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Triangulation
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Triangulation
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3-D Trilateration
1 Satellite
2 Satellites
3 Satellites
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Latitude and Longitude
Latitude
Longitude
Elevation
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Longitude
150 140 130 120 110
100 90
60 50 40 30 20 10 0
X
Latitude
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Line-of-sight

• Line of sight means the GPS unit needs to be in a
  visible line with the GPS satellites.

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Atomic Clocks

• GPS satellites use Atomic Clocks for accuracy,
  but because of the expense, most GPS receivers do
  not.

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Light Refraction

• Sometimes the GPS signal from the satellite
  doesnt follow a straight line.
• Refraction is the bending of light as it travels
  through one media to another.

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Signal Refraction

• Signals from satellites can be like light. When
  they hit some interference (air patterns in the
  atmosphere, uneven geography, etc.) they
  sometimes bend a little.

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Signal Interference

• Sometimes the signals bounce off things before
  they hit the receivers.

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Satellite Distribution

• When the satellites are all in the same part of
  the sky, readings will be less accurate.

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PDOP
PDOP Positional Dilution of Precision

• All of this combines to make the signal less
  accurate, and gives it what we call a high
  PDOP.

11,000 miles
11,000 miles
11,000 miles
11,000 miles

• A PDOP of lt4 is excellent
• A PDOP of 4-8 is good
• A PDOP of gt8 is poor

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In a Nutshell
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WAAS SystemWide Area Augmentation System

• WAAS is a system of satellites and ground
  stations that provide GPS signal corrections,
  giving five times better position accuracy.

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GPS Unit
Enter
Navigate
Power
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Satellite Screen
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Map Screen
You are here
IN
OUT
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Compass Screen
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Waypoints
Waypoints are locations or landmarks worth
recording and storing in your GPS. These are
locations you may later want to return to.
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GOTO Waypoint

• Menu button
• GOTO option
• User Waypoint
• Position
• Select waypoint
• Use Compass or Road screen to navigate back to
  waypoint.

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Questions

• Alana Jensen
• ESER Program
• S. M. Stoller Corp.
• 1780 First Street
• Idaho Falls, ID
• 208-525-9358
• ajensen_at_stoller.com
• www.stoller-eser.com

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Differential Correction

• Differential correction is a technique that
  greatly increases the accuracy of the collected
  GPS data. It involves using a receiver at a known
  location - the "base station- and comparing that
  data with GPS positions collected from unknown
  locations with "roving receivers."

ISU Base Station - http//134.50.65.125/
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Postprocessing / Real-time
Before
After
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Trimble GeoExplorer 3
EXTERNAL ANTENNA HOOKUP
SCREEN
ENTER button lets you select an option
OPTION button displays choices and menus in the
various screens
CLOSE button lets you cancel a feature or close a
menu box
ARROW BARS let you scroll up/down and left/right
SYSTEM button lets you scroll through the various
system screens
NAVIGATION button lets you scroll through the
different navigation screens
FUNCTION button is for working with system and
configurations
DATA button lets you scroll between the various
data screens
BATTERY COMPARTMENT
POWER button turns power on and off
LOG button allows you to pause/unpause satellite
communication for a time
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System

• See how many satellites are in communication
• Check level of memory and battery power
• Change data collection settings

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Data

• Data collection stored.
• Features updated
• Map of features
• New features added

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Navigation

• Maps to show where you are in relation to the
  place youre trying to get to.
• How fast youre walking or driving
• How far youve gone

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Collecting Data

• Circle represents horizon
• Numbers in circle represent satellites within
  horizon
• Black squares are locked-in satellites.
• White squares are satellites not locked in.
• No squares are satellites not communicating.
• Need a minimum of four satellites.

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Too few satellites

• Just a bad time of day.
• PDOP is set too high. (Hit Sys button twice)

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More System Tools

• Number of satellites
• Blinking number means not enough satellites
• Battery Level

These tools are always open no matter what screen
you are in.
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Data Screen

• Name your file

Dont change the first letter
Choose your data dictionary
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Data Dictionary

• GPS units collect data in
• Points
• Lines
• Areas
• These are called features.
• A data dictionary is a means by which we collect
  specific information about a data feature.

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Roving File

• A roving file is like a drawer of a filing
  cabinet containing many feature files.

Collect all the features collected in one
interval in one roving file.
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Navigation Screen

• Waypoint Navigation
• A waypoint (in its simplest terms) is just a
  location in latitude and longitude.
• Press option New Waypoint

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Latitude and Longitude

• Get latitude and longitude information from the
  bottom of the Nav Chart screen.

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Navigate to Waypoint

• Go to Navigate window and press Option.

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Navigation Compass
Shows which way is north in relation to where you
stand.
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Navigation Chart
Birds-eye-view of the place youre trying to get
to.
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Navigation Road
Close-up view of where your waypoint is in
relation to you.