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 idealised continuation of the mean surface of the oceans beneath the continents.

Photo of a geoid
Geoid

The geoid deviates globally from a mathematical reference surface (the rotation ellipsoid) by ±100 metres. The deviation from the local reference ellipsoid in Switzerland is ±5 metres.

The geoid can be determined with astro-geodetic and gravimetric methods. In the past few years it has become possible to determine the geoid «directly» through levelling and GNSS observations (GNSS-levelling).

Today the geoid model is indispensable, in particular for GNSS applications because it allows the easy transformation of ellipsoidal heights (h) determined by GNSS to the normally used orthometric heights (H), using the following simple formula: H = h - N

Graphic of a Geoid and Ellipsoid
Relationship between the geoid, ellipsoid and orthometric height

The Geoid in Switzerland

The geoid model in Switzerland (CHGeo2004) was determined through a combination of all methods and has an accuracy range of 1 to 3 centimetres.

The Swiss geoid model is available in the form of a 1-kilometre grid and can be integrated into practically all commercially available GNSS receivers.

The Geoid in Switzerland
Swiss geoid (CHGeo04) relative to the local reference ellipsoid.


Federal Office of Topography swisstopo Seftigenstrasse 264
P.O. Box
3084 Wabern
Tel.
+41 58 469 01 11

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Relevant authority

Geodesy and Federal Directorate of Cadastral Surveying
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Print contact

Federal Office of Topography swisstopo

Seftigenstrasse 264
P.O. Box
3084 Wabern

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