Undulation of the geoid

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Undulation of the geoid is a somewhat old-fashioned name for the separation <math>N</math> between the geoid and the reference ellipsoid of the Earth.

Because geophysical heights <math>H</math> "above sea level" refer to the geoid, but GPS positioning provides in a direct geometric fashion heights <math>h</math> above the GRS80 reference ellipsoid, it has become a matter of great importance to determine accurate representations, or maps, of geoid undulations

<math> N = h -H,\, </math>

over the territories of nations, to allow the inexpensive GPS technology to be harnessed for the precise determination of heights.

Reference

• "CHAPTER V PHYSICAL GEODESY", from the National Geodetic Survey web siteTemplate:Geo-term-stub