Editing Geodesy (section)

== Heights ==
{{further|Vertical position|Vertical datum}}
[[File:An-illustration-of-height-measurement-using-satellite-altimetry.jpg|285px|thumb|right|Height measurement using satellite altimetry]]

In geodesy, point or terrain ''[[height]]s'' are "[[above sea level]]" as an irregular, physically defined surface.
Height systems in use are:

# [[Orthometric height]]s
# [[Dynamic height]]s
# [[Geopotential height]]s
# [[Normal height]]s

Each system has its advantages and disadvantages. Both orthometric and normal heights are expressed in [[metre]]s above sea level, whereas geopotential numbers are measures of potential energy (unit: m<sup>2</sup> s<sup>−2</sup>) and not metric. The reference surface is the [[geoid]], an [[equigeopotential]] surface approximating the mean sea level as described above. For normal heights, the reference surface is the so-called ''[[quasi-geoid]]'', which has a few-metre separation from the geoid due to the density assumption in its continuation under the continental masses.<ref name="ForoughiTenzer2017">{{cite journal|last1=Foroughi|first1=Ismael|last2=Tenzer|first2=Robert|title=Comparison of different methods for estimating the geoid-to-quasi-geoid separation|journal=Geophysical Journal International|volume=210|issue=2|year=2017|pages=1001–1020|issn=0956-540X|doi=10.1093/gji/ggx221|doi-access=free |hdl=10397/75053|hdl-access=free}}</ref>

One can relate these heights through the [[geoid undulation]] concept to ''[[ellipsoidal height]]s'' (also known as ''geodetic heights''), representing the height of a point above the [[reference ellipsoid]]. [[Satellite positioning receiver]]s typically provide ellipsoidal heights unless fitted with special conversion software based on a model of the geoid.