Geodesy
Fundamentals Geodesy Geodynamics Geomatics History
Concepts Geographical distance Geoid Figure of the Earth(radius andcircumference) Geodetic coordinates Geodetic datum Geodesic Horizontal position representation Latitude / Longitude Map projection Reference ellipsoid Satellite geodesy Spatial reference system Spatial relations Vertical positions
Technologies Global Nav. Sat. Systems (GNSSs) Global Pos. System (GPS) GLONASS(Russia) BeiDou (BDS)(China) Galileo(Europe) NAVIC(India) Quasi-Zenith Sat. Sys. (QZSS)(Japan) Discrete Global Grid and Geocoding
Standards (history) NGVD 29 Sea Level Datum 1929 OSGB36 Ordnance Survey Great Britain 1936 SK-42 Systema Koordinat 1942 goda ED50 European Datum 1950 SAD69 South American Datum 1969 GRS 80 Geodetic Reference System 1980 ISO 6709 Geographic point coord. 1983 NAD 83 North American Datum 1983 WGS 84 World Geodetic System 1984 NAVD 88 N. American Vertical Datum 1988 ETRS89 European Terrestrial Ref. Sys. 1989 GCJ-02 Chinese obfuscated datum 2002 Geo URI Internet link to a point 2010 International Terrestrial Reference System Spatial Reference System Identifier (SRID) Universal Transverse Mercator (UTM)
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TheNational Geodetic Vertical Datum of 1929 (NGVD29), originally known as theSea Level Datum of 1929,^[1] is thevertical datum established for vertical controlsurveying in theUnited States of America by the General Adjustment of 1929. NGVD29 was determined and published by theUnited States Coast and Geodetic Survey^[2] and is used to measure theelevation of a point above and belowmean sea level (MSL).

NGVD29 was superseded by theNorth American Vertical Datum of 1988 (NAVD88),^[3] based upon reference to a single benchmark (referenced to the newInternational Great Lakes Datum of 1985 local mean sea level height value), although many cities andU.S. Army Corps of Engineers "legacy" projects with established data continued to use the older datum.^[4]

Mean sea level was measured at 26 tide gauges: 21 in the United States and five inCanada. 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 theadjustment of observations. The adjustment required a total of 66,315 miles (106,724 km) oflevelling 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 ofmean sea level, thegeoid, or any otherequipotential surface. Therefore, it was renamed the National Geodetic Vertical Datum of 1929 (NGVD 29) May 10, 1973, by theNational Geodetic Survey, a part of theNational Oceanic and Atmospheric Administration.^[1]

• Altitude
• Elevation
• Geodetic datum
• Geodesy
• Geoid
• Mean sea level
• North American Vertical Datum of 1988
• Reference ellipsoid
• Topography

• "United States Geological Survey home page".
• "U.S. National Geodetic Survey home page".
• "Geodetic Glossary".United States National Geodetic Survey.
• "Orthometric Height Conversion tool".United States National Geodetic Survey.

• 1929 in the United States
• Topography
• Surveying of the United States
• Vertical datums

• Articles with short description
• Short description matches Wikidata