Vertical References Change service

Vertical References Change service

The Change of Vertical References (CRV) service is only available with a subscription key which can be purchased on the Shom store: CRV.


Chart datum is the reference level for nautical charts and tide directories. This reference at sea is different from the reference for altitudes shown on land maps. Chart datum is defined near the level of the lowest astronomical seas. Two other important vertical references in hydrography are:

- the mean sea level, used in particular for modeling currents and waves;

- the level of the highest astronomical tide, which contributes to the definition of the coastline.

Advances in spatial geodesy techniques have generalized access to a new vertical reference: the ellipsoid. The ellipsoid is a mathematical modeling of the planet, it is possible to access the distance separating us from the latter using a GNSS receiver, for example.

This vertical reference change service makes it possible to modify a data file referenced from one reference level to another reference level.

The service works with version 1.1 of BathyElli surfaces.

References available

  • Ellipsoïde GRS80 associated to RGF93
  • Chart datum
  • Mean sea level
  • Lowest astronomical tide
  • Highest astronomical tide
  • Plus basses mers astronomiques
  • Plus hautes mers astronomiques
  • France's land datum (IGN69)