Editing Arc measurement (section)

{{Short description|Technique of determining the radius of Earth}}
[[File:Eratosthenes-Erdmessung.svg|thumb|Arc measurement of Eratosthenes]]

'''Arc measurement''',<ref name="Torge2012">{{cite book | last1=Torge | first1=W. | last2=Müller | first2=J. | title=Geodesy | publisher=De Gruyter | series=De Gruyter Textbook | year=2012 | isbn=978-3-11-025000-8 | url=https://books.google.com/books?id=RcfmBQAAQBAJ&pg=PA6 | access-date=2021-05-02 | page=5}}</ref> sometimes called '''degree measurement'''<ref>[[Wilhelm Jordan (geodesist)|Jordan, W.]], & Eggert, O. (1962). Jordan's Handbook of Geodesy, Vol. 1. Zenodo. http://doi.org/10.5281/zenodo.35314</ref> ({{langx|de|Gradmessung}}),<ref name="Torge 2008 p. 5">{{cite book | last=Torge | first=W. | title=Geodäsie | publisher=De Gruyter | series=De Gruyter Lehrbuch | year=2008 | isbn=978-3-11-019817-1 | url=https://books.google.com/books?id=lsO2uz_5euIC&pg=PA5 | language=de | access-date=2021-05-02 | page=5}}</ref> is the [[astrogeodetic]] technique of determining the [[radius of Earth]] and, by [[Circumference#Circle|extension]], [[Earth's circumference|its circumference]]. More specifically, it seeks to determine the local [[Earth radius of curvature]] of the [[figure of the Earth]], by relating the [[latitude]] difference (sometimes also the [[longitude]] difference) and the [[geographic distance]] ([[arc length]]) [[Surveying|surveyed]] between two locations on Earth's surface.<ref>{{Cite book |url=https://books.google.com/books?id=jPVxSDzVRP0C&dq=arc+measurement&pg=PA29 |title=Glossary of the Mapping Sciences |date=1994-01-01 |publisher=[[American Society of Civil Engineers]] (ASCE) |isbn=978-0-7844-7570-6 |language=en}}</ref> The most common variant involves only [[astronomical latitude]]s and the [[meridian arc]] length and is called ''meridian arc measurement''; other variants may involve only [[astronomical longitude]] (''[[parallel of latitude|parallel]] arc measurement'') or both [[geographic coordinates]] (''oblique arc measurement'').<ref name="Torge2012"/>
Arc measurement campaigns in Europe were the precursors to the [[International Association of Geodesy]] (IAG).<ref>{{Cite book|title=IAG 150 Years|volume = 143|last=Torge|first=Wolfgang|date=2015|publisher=Springer, Cham|pages=3–18|language=en|doi=10.1007/1345_2015_42|chapter = From a Regional Project to an International Organization: The "Baeyer-Helmert-Era" of the International Association of Geodesy 1862–1916|series = International Association of Geodesy Symposia|isbn = 978-3-319-24603-1}}</ref>
Nowadays, the method is replaced by worldwide [[geodetic network]]s and by [[satellite geodesy]].