Transcript What is GPS? - GSS ESER Program

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
GPS Uses
• Police and
Emergency
Medical
Services
• Firefighters
• Map makers
• Science
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.
GPS Units
1970s
Today
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.
DOD
• DOD checks position, altitude and speed
• Relay information to satellite
• Satellite broadcasts information to GPS units
Speed of Sound
Count the seconds
between the
lightning and the
thunder, then divide
by 5.
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.
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 11:00:00
GPS unit receives at 11:00:05
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
Triangulation
Geometric
Principle:
You can find one
location if you
know its distance
from other,
already-known
locations.
Triangulation
Triangulation
3-D Trilateration
1 Satellite
3 Satellites
2 Satellites
Latitude and Longitude
Latitude
Longitude
Elevation
150 °
Longitude
140 ° 130 ° 120 ° 110 ° 100 °
60°
Latitude
50 °
40 °
30 °
20 °
10 °
0°
X
90 °
Line-of-sight
Line of sight means the GPS unit
needs to be in a visible line with the
GPS satellites.
Atomic Clocks
GPS satellites use Atomic Clocks
for accuracy, but because of the
expense, most GPS receivers do
not.
Light Refraction
Sometimes the GPS
signal from the
satellite doesn’t
follow a straight line.
Refraction is the
bending of light as
it travels through
one media to
another.
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.
Signal Interference
Sometimes the
signals bounce off
things before they
hit the receivers.
Satellite Distribution
When the satellites are all in the same part
of the sky, readings will be less accurate.
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.”
•A PDOP of <4 is excellent
•A PDOP of 4-8 is good
•A PDOP of >8 is poor
11,000 miles
11,000 miles
11,000 miles
11,000 miles
In a Nutshell
WAAS System
Wide Area Augmentation System
WAAS is a system of satellites and ground
stations that provide GPS signal
corrections, giving five times better
position accuracy.
GPS Unit
Enter
Navigate
Power
Satellite Screen
Map Screen
You are here
IN
OUT
Compass Screen
Waypoints
Waypoints are locations
or landmarks worth
recording and storing in
your GPS. These are
locations you may later
want to return to.
GOTO Waypoint
•
•
•
•
•
•
Menu button
GOTO option
User Waypoint
Position
Select waypoint
Use Compass or Road screen to
navigate back to waypoint.
Questions
Alana Jensen
ESER Program
S. M. Stoller Corp.
1780 First Street
Idaho Falls, ID
208-525-9358
[email protected]
www.stoller-eser.com
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/
Postprocessing / Real-time
Before
After
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
FUNCTION button is for
working with system and
configurations
BATTERY
COMPARTMENT
NAVIGATION button
lets you scroll through
DATA button the different
navigation screens
lets you
scroll
between the
various data
screens
POWER button turns power on and off
LOG button allows you to pause/unpause
satellite communication for a time
System
• See how many
satellites are in
communication
• Check level of
memory and
battery power
• Change data
collection
settings
Data
• Data collection
stored.
• Features
updated
• Map of features
• New features
added
Navigation
• Maps to show
where you are in
relation to the
place you’re trying
to get to.
• How fast you’re
walking or driving
• How far you’ve
gone
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.
“Too few satellites”
• Just a bad time
of day.
• PDOP is set too
high. (Hit Sys button
twice)
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.
Data Screen
Name your file
Don’t change the
first letter
Choose your
data dictionary
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.
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.
Navigation Screen
• Waypoint
Navigation
– A waypoint (in its
simplest terms) is
just a location in
latitude and
longitude.
• Press option – New
Waypoint
Latitude and Longitude
Get latitude and
longitude
information from
the bottom of the
Nav Chart screen.
Navigate to Waypoint
Go to Navigate
window and press
Option.
Navigation Compass
Shows which way is north in relation to where you stand.
Your location
Direction to waypoint
Waypoint
Distance to waypoint
The angle you’re moving
in relation to north (N)
Navigation Chart
Bird’s-eye-view of the place you’re trying to get to.
Direction of waypoint
Your location
Waypoint
Date and
Time
Latitude and Longitude
Navigation Road
Close-up view of where your waypoint is in relation to you.
Your Destination
You
Waypoint
Your Speed
Distance to waypoint
Direction to waypoint