Geoid
The geoid is a selected equipotential surface of the earth's gravity field and serves as the reference surface for height determination. It can be considered as an idealized continuation of the mean surface of the oceans beneath the continents.
The geoid deviates globally from a mathematical reference surface (the rotation ellipsoid) by up to ±100 m. The deviation from the local reference ellipsoid in Switzerland reaches amounts up to ±5 m.
The geoid can be determined with astro-geodetic and gravimetric methods. In the last few years it became possible to determine the geoid «directly» from levelling and GPS observations (GPS-levelling).
Today the geoid model is indispensible in particular for GPS applications because it allows the easy transformation of ellipsoidal heights (h) determined by GPS to the normally used orthometric heights (H) with the following simple formula: H = h - N
- Geoid and Ellipsoid
The Geoid in Switzerland
The geoid model in Switzerland (CHGeo2004) was determined from a combination of all methods and shows an accuracy of 1 to 3 cm.
The Swiss geoid model is available in the form of a 1-km grid and can be integrated in practically all of the commercially available GPS receivers.
- Swiss geoid (CHGeo04) relative to the local reference ellipsoid.
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GeodesyLast updated: 16.08.2010
