Height datum relations
European national height reference systems
The vertical datum is determined by the mean sea level, which is estimated at one or more tide gauge stations. The tide gauge stations of the national European height systems in Europe are located at various oceans and inland seas: Baltic Sea, North Sea, Mediterranean Sea, Black Sea, Atlantic Ocean. The differences between these sea levels can come up to several decimeters. They are caused by the various separations between the ocean surface and the geoid.
In Europe three different kinds of heights (normal heights, orthometric heights and normal-orthometric heights) are used. Examples for the use of orthometric heights are Belgium, Denmark, Italy and Switzerland. Today normal heights are used in France, Germany, Scandinavia and in the most countries of Eastern Europe. In Austria and in the countries of the former Yugoslavia normal-orthometric heights are used.
Relations between European national height reference systems and EVRF2007
The below picture shows the reference tide gauges for European national height reference systems and the offsets to EVRF2007 in cm.
More detailed information about European coordinate reference systems and their transformation parameters to the pan-European Vertical Reference System EVRS are available at Information System for European Coordinate Reference Systems CRS-EU.