Lecture_07_GPS_1

Lecture_07_GPS_1 - http:/www.trimble.com/gps/whygps.shtml...

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http://www.trimble.com/gps/whygps.shtml
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GPS- Global Positioning System GPS uses: Satellites with hyper hyper -accurate clocks ( ), radio signals, and relatively inexpensive receivers Provides accurate location (lat/long/elev) for “any place on earth” using time-distance transformations. Originally developed for DoD but broadly adopted for civilian use. GPS has revolutionized revolutionized navigation, surveying, and other geospatial activities.
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GPS Satellite Facts Altitude: 10,900 nautical miles Weight:1900 lbs (in orbit) Size:17 ft with solar panels extended Orbital Period: 12 hours Planned Lifespan: 7.5 years The current GPS constellation consists of approx 32 Block II/IIA/IIR/IIR -M satellites
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The first Block II satellite was launched in February 1989; the most recent Block IIR-M satellite was launched on March 15, 2008. http://tycho.usno.navy.mil/gpscurr.html
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The GPS constellation Designed to ensure that multiple (at least 4) satellites are always “visible” from ground positions.
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Basic idea is to TRIANGULATE… The whole idea behind GPS is to use satellites in space as reference points for locations on earth. By very accurately measuring our distance from three satellites we can, THEORETICALLY, "triangulate" (actually this is trilateration- but triangulation seems entrenched) our position anywhere on earth. Four are needed to improve accuracy.
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GPS receivers can GPS receivers can be relatively large be relatively large
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or lightweight hand-helds devices… or lightweight hand-helds devices…
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or be in a or be in a wristwatch sized wristwatch sized device device or a cell phone. or a cell phone.
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http://en.wikipedia.org/wiki/File:ConstellationGPS.gif
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Suppose we measure our distance from one satellite and find it to be 12,000 miles.
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Knowing that we're 12,000 miles from a particular satellite narrows down all the possible locations we could be in the whole universe to the surface of a sphere centered on this satellite with a radius of 12,000 miles. http://www.trimble.com/gps/why.html
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Next, say we measure our distance to a second satellite and find out that it's 12,500 miles away. That tells us that we're not only on the first sphere but we're also on a sphere that's 12,500 miles from the second satellite. Or in other words, we're somewhere on the circle where these two spheres intersect. http://www.trimble.com/gps/why.html
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13,000 miles from that one, that narrows our position down even farther, to the two points where the 13,000 mile sphere cuts through the circle that's the intersection of the first two spheres. http://www.trimble.com/gps/why.html
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This note was uploaded on 04/01/2012 for the course 044 005 taught by Professor Davidbennett during the Fall '11 term at University of Iowa.

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Lecture_07_GPS_1 - http:/www.trimble.com/gps/whygps.shtml...

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