Geodesy
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Fundamentals
Geodesy · Geodynamics
Geomatics · Cartography
Concepts
Datum · Distance · Geoid
Figure of the Earth
Geodetic system
Geog. coord. system
Hor. pos. representation
Map projection
Reference ellipsoid
Satellite geodesy
Spatial reference system
Technologies
GNSS · GPS · GLONASS
Standards
ED50 · ETRS89 · GRS 80
NAD83 · NAVD88 · SAD69
SRID · UTM · WGS84
History
History of geodesy
NAVD29

The Sea Level Datum of 1929 was the vertical control datum established for vertical control surveying in the United States of America by the General Adjustment of 1929. The datum was used to measure elevation (altitude) above, and depression (depth) below, mean sea level (MSL).

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. The adjustment required a total of 66,315 miles (106,724 km) of leveling 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) in 1973. The NGVD 29 was subsequently replaced by the North American Vertical Datum of 1988 (NAVD 88) based upon the General Adjustment of the North American Datum of 1988.

See also

External links