![]() NAVD 88 should not be used as Mean Sea Level.Īdopted as a standard geodetic datum for elevations determined by See International Great Lakesĭatum of 1985, National Geodetic Vertical Datum of 1929, and ![]() However, NAVD 88īench mark values are given in Helmert orthometric height units while Point, Rimouski, Quebec, Canada was held fixed, thus providing minimumĬonstraint. Primary tidal bench mark, referenced to the International Great Lakesĭatum of 1985 (IGLD 85) local mean sea level height value, at Father In the adjustment, only the height of the The datum was derived from a generalĪdjustment of the first-order terrestrial leveling nets of the United North Americanįor elevations determined by geodetic leveling. Vertical datums are used to measure elevations or underwater depths. Horizontal datums are used for describing a point on the earth's surface, in latitude and longitude. In surveying and geodesy, a datum is a reference point on the earth's surface against which position measurements are made, and an associated model of the shape of the earth for computing positions. "A set of constants used for calculating the coordinates of points on the Earth." Generally a datum is a reference from which measurements are made. The National Geodetic Survey (NGS) defines a geodetic datum as: 1.
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