Orthometric height: Difference between revisions
BillHart93 (talk | contribs) Undid revision 553708783 by Tim Zukas Undo imprecise definition |
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The '''orthometric height''' is the distance H along a line of force from |
The '''orthometric height''' of a point P is the distance H along a gravitational line of force from the point at the physical surface to the [[geoid]]. |
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Orthometric heights are what are usually used in the US for ordinary engineering work. Values for measured points can be obtained from the National Geodetic Survey data sheets.<ref>http://www.ngs.noaa.gov</ref> This data was gathered over many years by massive projects of precise optical leveling. |
Orthometric heights are what are usually used in the US for ordinary engineering work. Values for measured points can be obtained from the National Geodetic Survey data sheets.<ref>http://www.ngs.noaa.gov</ref> This data was gathered over many years by massive projects of precise optical leveling, and was corrected for variations in gravity that cause discrepancies in optical leveling over large regions. |
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Orthometric heights relate approximately to the "height above [[sea level]]" but the current [[NAVD88]] datum is tied to a specific elevation at a chosen point rather than to any location's exact mean sea level. |
Orthometric heights relate approximately to the "height above [[sea level]]" but the current [[NAVD88]] datum is tied to a specific elevation at a chosen point rather than to any location's exact mean sea level. |
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Revision as of 02:32, 7 May 2013
 | This article needs additional citations for verification. (December 2009) |
The orthometric height of a point P is the distance H along a gravitational line of force from the point at the physical surface to the geoid.
Orthometric heights are what are usually used in the US for ordinary engineering work. Values for measured points can be obtained from the National Geodetic Survey data sheets.[1] This data was gathered over many years by massive projects of precise optical leveling, and was corrected for variations in gravity that cause discrepancies in optical leveling over large regions.
Orthometric heights relate approximately to the "height above sea level" but the current NAVD88 datum is tied to a specific elevation at a chosen point rather than to any location's exact mean sea level.
GPS measurements give earth-centered coordinates, usually displayed as height above the reference ellipsoid, which cannot be related accurately to orthometric height above the geoid unless accurate gravity data is available for that location. NGS is undertaking the GRAV-D program to obtain such data.[2]
Alternatives to orthometric height include dynamic height and normal height.
References
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