Transcript Introduction To Global Positioning System and other Geo

Introduction To Global
Positioning System and
other Geo-technologies
Lecturer – Jun Liang
Office – 218 Saunders
Lecture 1 – Basic Concepts
Location Problem Examples –
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Point: Where am I? Tree location; 911
calling stations;
Line: Bike trails; New streets; animal
activities;
Polygon: land parcels; buildings; water body;
Methods –
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Traditional Survey; New technologies –
Navigation Star.
NAVSTAR
NAVigation System with Time And
Ranging (Navigation Star”) – A
constellation of from 24 to 32 satellites
orbiting the Earth, broadcasting data that
allows users on or near the Earth to
determine their spatial positions. GPS in
USA. Russians – GLONASS.
Coordinates and References
2D – latitude and longitude (actually it is
3D, since diameter of Earth is not a
constant value.)
Absolute VS relative coordinates
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References – Sun, Earth, Chapel Hill, Durham,
Saunders Hall, Old Well, Control points, etc.
Recording: 38N, 84.5W; 100 Meters east of
Saunders Hall; 50 Miles West of Raleigh
Positions from GPS
Absolute Positions – could be reset in GPS
receivers.
Latitude, Longitude => UTM
Latitude, Longitude => SPC
Advantages of using GPS:
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High positioning accuracy, from meters down to the
millimeter level
Availability
Capability of determining velocity and time, to an
accuracy commensurate with position.
Time/Velocity
No inter-station visibility
Anatomy of the term: “Global
Positioning System”
Global: anywhere on Earth, but not:
Inside buildings
 Underground
 In very heavy tree canopy
 Around strong radio transmissions
 In “urban canyons” amongst tall buildings
 Near powerful radio transmitter antennas
Or anywhere else not having a direct view of a
substantial portion of the sky.
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Anatomy of the term: “Global
Positioning System” (Cont.)
Positioning –
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Where are you?
How fast are you moving and in what direction?
In what direction should you go to get to some
other specific location
How long would it take at your speed to get
there?
Where have you been?
Anatomy of the term: “Global
Positioning System” (Cont.)
System: A collection of components with
connections (links) among them:
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The Earth
Earth-Circling Satellites
Ground-Based Stations
Receivers
Receiver Manufacturers
The United States Department of Defense
Users
The Earth
The mass of the Earth holds the satellites
in orbit – each satellites is trying to fly by
the Earth at 4KM per second.
The surface of the Earth is studded with
little “monuments” – whose coordinates
are known quite accurately, allow us to
determine the position of any objects we
choose on the surface of the Earth.
Earth-Circling Satellites
24-32 solar-powered radio transmitters
Forms a constellations such that several are
“visible” from any point on Earth at any given
time
First one Feb 22, 1978; Mid-1994 all 24.
3/24 are spares
Block IIR – middle altitude (20,400 Km), below
geostationary satellites (35,763 Km).
Earth-Circling Satellites (Cont.)
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NAVSTAR satellites
Neither polar nor equatorial, but slice the
Earth’s latitudes at about 55 degree.
Executing a single revolution every 12
hours.
There are 6 distinct orbital planes (A, B, C,
D, E, F)
There 4 or 5 satellites in each planes.
Earth-Circling Satellites (Cont.)
A satellite has three key pieces of hardware:
Computer
Atomic Clock
Radio transmitter
All GPS Satellites carry NUDET sensors.
Earth-Circling Satellites (Cont.)
Speed - 3.87 km/sec
Weight – 1077 Kg
Length – 11.6 meter
Solar panel – 1100 watts (The radio on board
uses 40 watts); also has backup battery installed
(solar eclipse)
Two Radio channels – L1(1575.42 Mhz) and L2
(1227.6 MHz)
Each has 4 atomic clocks. (a billionth of a second)
Each is worth $65 million and can last 10 years.
Ground Based Stations
GPS Satellites’ tracks are influenced by
(1) gravitational effects of the moon and sun
(2) Solar wind
(3) System error
Thus both their tracks and innards requires
monitoring.
GPS ground stations are used to control GPS
movements and maintain accurate system
setting (such as removing clock errors.)
Ground Based Stations (Cont.)
There are five ground facility stations:
Hawaii, Colorado Springs, Ascension
Island, Diego Garcia and Kwajalein.
All stations are operated by the US
Department of Defense
All five stations are Monitor Stations,
equipped with GPS receivers to track the
satellites. The resultant tracking data is
sent to the Master Control Station (MCS).
Ground Based Stations (Cont.)
Each satellite passes over at least one
monitoring station twice a day.
Information
developed by the
monitoring station
•Health of the SAT
Rebroadcasts
to receivers
•Real tracks VS
expected tracks
•Current almanac for
all SAT
•Other subjects
Ground Based Stations (Cont.)
Almanac – a description of the predicated
positions of heavenly bodies.
Ephemeris - contains orbital information
that allows the receiver to calculate the
position of the satellite.
Clock information – Coarse Acquisition
(C/A) code and Precise (P) Code.
Ground Based Stations (Cont.)
Colorado Springs is the MCS, where the
tracking data processed in order to compute the
satellite ephemerides (or coordinates) and
satellite clock error parameters. It is also the
station that initiates all operations of the space
segment, such as spacecraft maneuvering,
signal encryption, satellite clock-keeping, etc.
Three of the stations (Ascension Is., Diego
Carcia, and Kwajalein) are Upload Stations
through which data is telemetered to the
satellites.
Receivers
GPS receivers consists of
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An antenna
Electronics
A microcomputer
Controls (buttons, keys)
A screen
Computer memory
Radio
Etc.
Receivers (Cont.)
GPS units receive two types of data from
NAVSTAR satellites:
Almanac
Ephemeris
Channels
Originally 4-5
Now most 12- 20
Receivers (Cont.)
Garmin
Left – ETREX 12 Channels
Right - GPSMAP60 12 Channels
Trimble
XT, XH handhelds – 12 Channels
MS860™ receiver is a 36-channel L1/L2
RTK GPS receiver
Receivers (Cont.)
Differential Corrections
Using the RTCM (Radio Technical
Commission for Maritime Services) SC104 format input
Low cost WAAS (Wide Area Augmentation
System) receiver
From GPS to PC or other devices - using
the NMEA0183 protocol
Receivers (Cont.)
Other protocols – SiRF
SiRF is a brand of microcontroller designed
to be used with GPS systems.
SiRFstar III – used by Garmin, Tomtom and
Magellan and other GPS manufactures.
Faster fix time
Higher signal locking and tracking
sensitivity
lower power requirements
Receivers (Cont.)
Receiver types
Consumer models
U.S. military/government models
Mapping/resource models
Survey models
Commercial transportation models
Receivers (Cont.)
Consumer models
Big three – Garmin (www.garmin.com),
Magellan (www.magellangps.com) and
Lowrance (www.lowrance.com)
Most are 12-channel parallel receivers
Prices are reasonably low – less than
$100
Location precision is low (15 meter most)
Receivers (Cont.)
U.S. military/government models
Can receive P-code and Y-code (only to
the government.)
Called PLGR (Precision Lightweight GPS
Receivers) - http://army-gps.robins.af.mil/
Accuracy – within 4 meters
Light Weight and no need to post
processing
Receivers (Cont.)
Mapping/resource models
Data can be input into a GIS application
More precise than consumer models –
from submeter to several meters
More expensive – A Trimble XH handheld
costs about $5000, and A XT costs about
$4000.
Receivers (Cont.)
Survey models
Purpose – surveying land, access
points, sampling of small objects
Extremely precise – down to
centimeter/millimeter
Tends to be large and complex to
use
Very expensive
Where did I put
it?
Receivers (Cont.)
Commercial transportation models
These GPS receivers are usually installed in
moving objects (aircraft, ships, cars,
trucks, etc.)
Provide navigation supports (where am I
type questions; optimizing routes; finding
service facilities etc.)
Can send location info to a monitoring
facility through APRS.
Manufacturers, DOD and Users
Manufacturers http://gauss.gge.unb.ca/manufact.htm
Note: some just manufacture GPS “engine”,
the other may provide a computer unit.
DOD manages GPS satellites and ground
control units. (SA was turned off by DOD
on May 2000)
Users – more people than ever are using
GPS, it will become as popular as MP3.
Other positioning systems
Galileo
EU and USA agreed on March 2002 to introduce
their own alternative to GPS, called Galileo.
The first satellite was actually launched on 28
December 2005.
The receivers will be able to combine the signals
from 30 Galileo and 28 GPS satellites to greatly
increase the accuracy.
The System will be working from 2010.
Other positioning systems
GLONASS
It is operated for the Russian government.
The first test SATs were launched in 1982
44 were launched by 1991
The constellation was not completed until
December 1995
Only eight SATs in operation in April 2002