The National Geodetic Vertical Datum of 1929 is the official name since 1973
of the
vertical datum established for vertical control
surveying
Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ca ...
in the
United States of America by the General Adjustment of 1929. Originally known as Sea Level Datum of 1929, NGVD 29 was determined and published by the
National Geodetic Survey and used to measure the
elevation of a point above and
depression below
mean sea level (MSL).
NGVD29 was superseded by the
North American Vertical Datum of 1988
The North American Vertical Datum of 1988 (NAVD 88) is the vertical datum for orthometric heights established for vertical control surveying in the United States of America based upon the General Adjustment of the North American Datum of 1988.
...
(
NAVD 88), based upon reference to a single benchmark (referenced to the new International Great Lakes Datum of 1985 local mean sea level height value), although many cities and
U.S. Army Corps of Engineers "legacy" projects with established data continued to use the older datum.
Methodology
Mean sea level was measured at 26 tide gauges: 21 in the United States and 5 in
Canada. The datum was defined by the observed heights of mean sea level at the 26 tide gauges and by the set of elevations of all bench marks resulting from the
adjustment of observations. The adjustment required a total of 66,315 miles (106,724 km) of
levelling with 246 closed circuits and 25 circuits at sea level.
Since the Sea Level Datum of 1929 was a hybrid model, it was not a pure model of
mean sea level, the
geoid, or any other
equipotential surface. Therefore, it was renamed the National Geodetic Vertical Datum of 1929 (NGVD 29) by the National Geodetic Survey (then, and since, under the auspices of
NOAA
The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...
) May 10, 1973.
[
]
See also
* Altitude
* Elevation
* Geodetic datum
* Geodesy
Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure (geometric shape and size), orientation in space, and gravity. The field also incorporates studies of how these properties change over time and equivale ...
* Geoid
* Mean sea level
* North American Vertical Datum of 1988
The North American Vertical Datum of 1988 (NAVD 88) is the vertical datum for orthometric heights established for vertical control surveying in the United States of America based upon the General Adjustment of the North American Datum of 1988.
...
* Reference ellipsoid
An Earth ellipsoid or Earth spheroid is a mathematical figure approximating the Earth's form, used as a reference frame for computations in geodesy, astronomy, and the geosciences. Various different ellipsoids have been used as approximations ...
* Topography
References
External links
*
*
*
* {{cite web , url=http://www.ngs.noaa.gov/cgi-bin/VERTCON/vert_con.prl , title=Orthometric Height Conversion tool , publisher= United States National Geodetic Survey
1929 in the United States
Topography
Surveying of the United States
Vertical datums