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Date: December 29, 2007 |
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Global Positioning System |
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The Global Positioning System (GPS) is a worldwide
radio wave navigation system formed from a constellation of
24 satellites and their ground stations to determine
accurate location and time. It was developed by the U.S.
Department of Defense with the primary purpose of enhancing
the effectiveness of U.S. and allied military forces. GPS is
rapidly becoming an integral component of the emerging
Global Information Infrastructure, with applications ranging
from mapping and surveying to international air traffic
management and global change research.
These days people from different walks of life are using GPS
in ways that make their work more productive, safer, and
sometimes even easier.
The real-world applications of GPS fall into five broad
categories:
Location
The first application of GPS is the determination of a
"position" or location. GPS is the first positioning system
to offer highly precise location data for any point on the
planet, in any weather.
Navigation
Navigation is the process of getting something from one
location to another. GPS helps to determine exactly where we
are, but sometimes important to know how to get somewhere
else. It was originally designed to provide navigation
information for ships and planes.
Tracking
Tracking is the process of monitoring the movement of people
and things as it moves along. GPS used in effective fleet
management.
Mapping
Mapping means creating maps of the world. It is a big world
out there, and using GPS to survey and map it precisely
saves time and money.
Timing
GPS used to disseminate precise time, time intervals, and
frequency. It makes the job of "synchronizing our watches"
easy and reliable.
GPS receivers integrate a radio and a navigation computer
and can receive the faint, twenty-watt signals coming from
the satellites. The computer uses these signals to calculate
the distance between the satellites and the receiver. With
this information, the computer can further calculate the
position and velocity of the receiver.
The number of satellites visible to a receiver constantly
varies between four and eleven according to time and
location. Each satellite broadcasts a number of unique
spread-spectrum codes, but only one, the Coarse Acquisition
(C/A) code, is easily accessible for civilian use. Code is
effectively a timing signal synchronized to an international
time standard-Universal Coordinated Time (UCT). |
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Global Positioning
System (GPS) |
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DGPS (Differential GPS)
Basic GPS is the most accurate radio-based navigation system
ever developed. And for many applications it's plenty
accurate. But it's human nature to want MORE! Differential GPS
is a way to correct the various inaccuracies in the GPS system
and pushing its accuracy even farther.
DGPS uses correction signals from one of four (4) sources for
improving accuracy:
Coast Guard Beacon
Coast Guard Beacon Correction is a signal based off towers
set-up. These towers act as both the reference location and
the transmission site. A benefit of this type of transmission
is its ability to follow the contour of the ground better than
higher frequency signals. However, this can allow bad weather,
such as thunderstorms, to affect performance of the system.
WAAS (Wide Area Augmentation System)
WAAS, formally called the Wide Area Augmentation System, is a
correction source designed for the FAA (Federal Aviation
Administration). "Augmented GPS” uses a geostationary
satellite as a relay station for the broadcast of corrections.
This tool has been put in place to assist aircraft
positioning.
Omnistar
Omnistar is a privately held company that provides
subscriptions for GPS correction. A user would select which
zone he is operating in and Omnistar provides the corrections
accordingly. A new correction source called Omnistar HP is a
newer signal and provides customers with a higher level of
accuracy (decimeter).
RTK (Real Time Kinematics)
Real Time Kinematics corrections are achieved by using a local
base station that contains both a GPS receiver for positioning
and radio for transmitting to a mobile unit. This technology
is a more advanced form of positioning that allows for
activities such as steer assist products, elevation mapping,
and surveying.
More can be found on:
http://www.beaglesoft.com/gpstechnology.htm
http://electronics.howstuffworks.com/gps.htm |
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