' ("standard elevation zero") or NHN is a

vertical datum In geodesy, surveying, hydrography and navigation, vertical datum or altimetric datum, is a reference coordinate surface used for vertical positions, such as the elevations of Earth-bound features (terrain, bathymetry, water level, and built str ...

used in Germany. In geographical terms, NHN is the reference plane for the normal height of a topographical eminence

height above mean sea level Height above mean sea level is a measure of the vertical distance (height, elevation or altitude) of a location in reference to a historic mean sea level taken as a vertical datum. In geodesy, it is formalized as '' orthometric heights''. The c ...

used in the 1932 German Mean Height Reference System ('). The plane is in the shape of a quasi-

geoid The geoid () is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth's rotation, if other influences such as winds and tides were absent. This surface is extended ...

. The reference height is a

geodetic Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure (geometric shape and size), orientation in space, and gravity. The field also incorporates studies of how these properties change over time and equivale ...

, fixed point on the New Church of St. Alexander at Wallenhorst in the German state of

Lower Saxony Lower Saxony (german: Niedersachsen ; nds, Neddersassen; stq, Läichsaksen) is a German state (') in northwestern Germany. It is the second-largest state by land area, with , and fourth-largest in population (8 million in 2021) among the 16 ...

. The

geopotential height Geopotential height or geopotential altitude is a vertical coordinate referenced to Earth's mean sea level, an adjustment to geometric height (altitude above mean sea level) that accounts for the variation of gravity with latitude and altitude. ...

of this point was calculated in 1986 as part of the United European Levelling Network (UELN), based on the Amsterdam Ordnance Datum.

Definition

The NHN plane is a theoretical reference plane. It is derived by deducting normal heights from the normal

plumb line A plumb bob, plumb bob level, or plummet, is a weight, usually with a pointed tip on the bottom, suspended from a string and used as a vertical reference line, or plumb-line. It is a precursor to the spirit level and used to establish a vertic ...

. The difference between the resulting quasi-geoid and the

reference ellipsoid An Earth ellipsoid or Earth spheroid is a mathematical figure approximating the Earth's form, used as a reference frame for computations in geodesy, astronomy, and the geosciences. Various different ellipsoids have been used as approximations ...

is called the height anomaly or quasi-geoid height.

Change-over from NN to NHN

Since 1 January 2000 the whole of Germany has changed its height system over to normal heights based on the

datum In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted. ...

of the Amsterdam Ordnance Datum, known as the German Mean Height Reference System, DHHN92. At the same time the new NHN is the basis of the United European Levelling Net (UELN), formerly known as the ' or , which standardises the height systems of the European countries. Heights in this system are given in metres above NHN or m (NHN). The NHN was introduced because for heights above the actual gravitational field of the earth was not taken into account. As a result, there were changes in both the old West German normal orthometric heights (new methods of calculation) and the normal heights of East Germany (with respect to the Amsterdam Datum). The elevations differed — depending on location — by 0.06 to 0.16 metres. As a result of new measurements as part of the changeover, however, variations of 0.59 metres () have surfaced. Older relief maps often show heights above the old reference planes. Current maps by the federal survey authorities are based on NHN. At the beginning of 2013 most of the federal states (except Berlin, Thuringia and Saxony-Anhalt) had complete coverage by the new digital topographic mapping at 1:25,000 scale (DTK). Not all the maps have appeared in print yet. On the DTK25 maps, NHN is used for elevations, however, on the DTK25-V scanned topographic maps (HN) and (NN) are still being used.

Old East German height system

East Germany East Germany, officially the German Democratic Republic (GDR; german: Deutsche Demokratische Republik, , DDR, ), was a country that existed from its creation on 7 October 1949 until German reunification, its dissolution on 3 October 1990. In t ...

normal heights used to be referred to as heights above or HN. The 1958 Kronstadt Tide Gauge (') was used as the datum. The new NHN heights are typically 12–15 cm higher. The maximum deviations in the

spirit level A spirit level, bubble level, or simply a level, is an instrument designed to indicate whether a surface is horizontal (level) or vertical ( plumb). Different types of spirit levels may be used by carpenters, stonemasons, bricklayers, ...

points of first order are between 7 and 16 cm.

References

External links

Description of NHN system

{{DEFAULTSORT:Normalhohennull Vertical datums Zero-level elevation points