National Geodetic Vertical Datum of 1929

The National Geodetic Vertical Datum of 1929 is the official name since 1973^[1] of the vertical datum established for vertical control surveying 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 United States Coast and Geodetic Survey^[2] and used to measure the elevation of a point above and depression below mean sea level (MSL).

Illustration of vertical datums in the United States.

NGVD29 was superseded by the North American Vertical Datum of 1988 (NAVD 88),^[3] based upon reference to a single benchmark (referenced to the new International Great Lakes Datum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.^[4]

Methodology

Mean sea level was measured at 26 tide gauges: 21 in the United States and five 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) May 10, 1973, by the National Geodetic Survey, a part of the National Oceanic and Atmospheric Administration.^[1]

See also

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

References

1. US Department of Commerce, National Oceanic and Atmospheric Administration. "National Geodetic Vertical Datum of 1929 (NGVD 29) - Vertical Datum - Datums - National Geodetic Survey". www.ngs.noaa.gov. Retrieved 2022-02-01.
2. .esri.com GIS Dictionary: National Geodetic Vertical Datum of 1929 Accessed November 18, 2023
3. US Department of Commerce, National Oceanic and Atmospheric Administration. "North American Vertical Datum of 1988 (NAVD 88) - Vertical Datum - Datums - National Geodetic Survey". www.ngs.noaa.gov. Retrieved 2022-02-01.
4. "Standards and Procedures for Referencing Project Elevation Grades to Nationwide Vertical Datums" (PDF).

External links

• "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.