Understanding GPS: Difference between revisions
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The US GPS system is a collection of 24 space vehicles placed in an approximately 12 hour orbit at +/- 55 degrees lattitude around the earth. By knowing exactly where these satalites are with regard to the earth, comunication with a GPS device can be trilaterated to calculate it's postition as well. GPS delivers to us 4 peices of data. Longitude, Latitude, Altitude, and Time. | |||
===Earth is a rock=== | |||
The Earth is not spherical. Neither is it an ellipsoid, although we use an ellipsoid to approximated it. The Earth is actually a geoid, or shaped like a rock. | |||
[[Image:Geoid.gif|left|frame|http://www.esri.com]] | |||
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===The System=== | |||
The standard for this is constantly in a state of flux, but at this moment, the system is defined by the WGS-84 standard. | |||
<br><br> | |||
[[http://www.pvdwiki.com/images/5/5a/WGS84_Manual.pdf WGS84 Implementation Manual]]<br><br> | |||
[[Image:Wgs.gif|left|frame|www.wgs84.com.com]] | |||
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[[Image:Orbitgu.jpg|left|frame|300px|"A plane (as in a flat surface) at 55 degrees to the equatorial plane. That orbital plane will have at least 4 SVs. Repeat this every 60 degress for a total of 6 orbital planes" abadfish]] | |||
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Europe has been working on developing their own Galileo GPS system, mainly in the interest on not relying on a US system that can be locked out as a negotiating tactic. Russia uses it's own GLONASS system. | |||
===Mathmatics=== | |||
[[Image:Ellipsegraphic.gif|left|frame|WGS-84 Implimentation Manual, p.70]] | |||
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[[Image:GPSpositioning.gif]] | |||
The earth surface can be approximated as an Oblate Sphereoid or Oblate Ellipsoid. The GPS system uses a definition contained in WGS-84. This model has an equitorial radius of 20925646 feet and a polar radius of 20855487 feet. | |||
F = (x/a)^2 + (y/b)^2 + (z/c)^2 where a = b = 20925646 and c = 20855487. | |||
[[Image:Ellipsoid-math.gif|left|frame|WGS-84 Implimentation Manual, p.81]] | |||
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===Hardware Suppliers=== | |||
Garmin<br> | |||
Megellen<br> | |||
[http://www.trimble.com/index.aspx Trimble] - Highly accurate GPS. Survey grade.<br> | |||
===External Links=== | |||
[http://en.wikipedia.org/wiki/Gps Wikipedia - GPS]<br> | |||
[http://en.wikipedia.org/wiki/Category:GPS Wikipedia Category - GPS] | |||
[http://www.trimble.com/gps/index.shtml Trimble - Understanding GPS] | |||
[[category:GPS]] | [[category:GPS]] | ||
Latest revision as of 20:37, 7 November 2006
The US GPS system is a collection of 24 space vehicles placed in an approximately 12 hour orbit at +/- 55 degrees lattitude around the earth. By knowing exactly where these satalites are with regard to the earth, comunication with a GPS device can be trilaterated to calculate it's postition as well. GPS delivers to us 4 peices of data. Longitude, Latitude, Altitude, and Time.
Earth is a rock
The Earth is not spherical. Neither is it an ellipsoid, although we use an ellipsoid to approximated it. The Earth is actually a geoid, or shaped like a rock.
The System
The standard for this is constantly in a state of flux, but at this moment, the system is defined by the WGS-84 standard.
[WGS84 Implementation Manual]
Europe has been working on developing their own Galileo GPS system, mainly in the interest on not relying on a US system that can be locked out as a negotiating tactic. Russia uses it's own GLONASS system.
Mathmatics
The earth surface can be approximated as an Oblate Sphereoid or Oblate Ellipsoid. The GPS system uses a definition contained in WGS-84. This model has an equitorial radius of 20925646 feet and a polar radius of 20855487 feet.
F = (x/a)^2 + (y/b)^2 + (z/c)^2 where a = b = 20925646 and c = 20855487.
Hardware Suppliers
Garmin
Megellen
Trimble - Highly accurate GPS. Survey grade.
