Taking it to the next level:
CORS and GIS |
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The Continuously Operating Reference Stations
(CORS) system is
a network that continually
corrects GPS signals,
and provides these
corrections to GPS
users over the Internet. Click
on the image for larger
view.
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In a field of study that is thousands of years
old, GPS represents a quantum leap in geodesy. As
advanced as GPS technology is, most commercially
available GPS receivers are only accurate within
several meters. Considering that the Earth is almost
25,000 miles in circumference, the difference of
a few meters may not seem important. This level of
accuracy may be adequate for a hiker in the woods
or someone driving a car. But there are many scientific,
military, and engineering activities that require
much higher levels of positioning accuracy - often
to within a few centimeters or less!
To provide measurements at this level of accuracy, NGS developed the Continuously Operating Reference Stations (CORS) network. CORS is a network of hundreds of stationary, permanently operating GPS receivers throughout the United States. Working 24 hours a day, seven days a week, CORS stations continuously receive GPS radio signals and integrate their positional data into the National Spatial Reference System. This data is then distributed over the Internet. After logging onto the CORS Web site, users can determine the accuracy of their coordinates to the centimeter. This system has been especially useful in assessing the integrity of buildings and bridges in areas that are geologically active or have been impacted by natural disasters such as hurricanes or floods.
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Information
about a place in a GIS is stored
in several separate but overlapping
layers that represent utility lines, buildings, roads, aerial photography, and
topography. Click
on the image for larger
view and animation. |
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Another powerful tool that has evolved along
with GPS technology is the Geographic Information System (GIS). A GIS
is comprised of three parts: spatial information,
special software, and a computer. These components work together to
provide a digital platform for viewing and processing layers of spatial
information.
A
GIS assembles information from a several of sources,
including ground surveys, existing maps, aerial photos,
and satellite imagery. In a GIS, specific information
about a place, such as the locations of utility lines,
roads, streams, buildings, and even trees and animal
populations, is layered over a set of geodetic data.
Using special software, regional planners and scientists
can examine the layers individually or in various
combinations to improve traffic flow, merge construction
with utility systems, develop around environmentally sensitive
areas, and protect the public from potential natural
disasters. Because a GIS stores data digitally, information
can be quickly and economically updated, easily reproduced,
and made widely available. In fact, because of its
power and speed, GIS technology is doing most of the cartographic (mapmaking)
work that, in the past, was laboriously done by hand on
paper charts and maps.
The most important element needed to reconstruct geographic reality in a GIS is good spatial information. If the spatial information provided to a GIS is sparse or of poor resolution, then the world created by the computer will be a lifeless digital shell -- a sharp contrast to the complexity of our living Earth.
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