Geography Reference
In-Depth Information
POINT
The GPS is a network of twenty-four satellites and five ground stations designed
to provide anyone carrying a portable satellite receiver with a highly specific
determination of his or her location, anywhere, anytime, and in any weather. It
promises that people and their vehicles will never get lost ...missiles and bombs, as
well as airplanes, will land exactly where they ought to...and a world of stationary
objects, from telephone poles to wetlands to private homes, will be fixed once and
for all in their proper places.
How to locate a point with GPS? Stand somewhere open to the sky with a GPS
receiver for ten minutes and collect a stream of position readings [ SCATTER].
Atmospheric interference, military scrambling, and the “multipathing” bounce of
the signals in a built environment combine to represent that stationary position as
a complex scattering of points. Download the data to a computer from the receiver,
and then download from a local base station its (scattered) readings for the same
time period. Correct your readings and reduce the drift [ CORRECTION], average
the points, and learn where you were...within a few meters. In the computer, the
satellites draw the points for you, and as the readings become more precise, the
points grow to fill the screen [POINT].
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