Airy spheroid

The '''Airy spheroid''' or '''Airy ellipsoid''' is a mathematical model of the Earth, an [[Earth ellipsoid]], designed to fit the well for the [[British Isles]]. It is named after its inventor [[George Biddell Airy]], a nineteenth century English mathematician.

==Airy 1830 ellipsoid== The Airy 1830 ellipsoid has an equatorial radius of 6,377,563.396 m, a polar radius of 6,356,256.909 m and an inverse flattening of 299.3249646.

The original definition was in [[foot (unit)|feet]] - using the 1796 definition of the foot, an equatorial radius of 20,923,713 ft and a polar radius of 20,853,810 ft.<ref name=epsg7001>{{Cite web|url=https://epsg.io/7001-ellipsoid|title=Airy 1830 - EPSG:7001 |website=epsg.io}}</ref> When the [[Ordnance Survey]] retriangulated in 1936 they defined a conversion to [[metres]], namely a ratio of (10^0.48401603)/10 which is approximately 1 ft = 0.3048007491 m.<ref name=epsg7001 />

==Airy Modified 1849== The 1849 ellipsoid (EPSG:7002), known as Airy Modified 1849, is the 1830 ellipsoid scaled by 0.999965 to better fit the primary triangulation of Ireland.<ref>{{Cite web|url=https://epsg.io/7002-ellipsoid|title=Airy Modified 1849 - EPSG:7002 |website=epsg.io}}</ref>

==See also== * [[Ordnance Survey National Grid]] * [[Irish grid reference system]]

==References== {{Reflist}}

==Further reading== * {{cite journal |last=Airy |first=George Biddell |title=XXXIII. On the figure of the earth |journal=Philosophical Transactions of the Royal Society of London |volume=116 |year=1826 |pages=548-578 }} * {{cite book |title=6th International Conference on Cargography and GIS |year=2016 |editor1-last=Bandrova |editor1-first=Temenoujka |editor2-last=Konečný |editor2-first=Milan |publisher=Bulgarian Cartographic Association |chapter=George Biddell Airy and his Contribution to Map Projections Theory |last=Lapaine |first=Miljenko |url=https://www.researchgate.net/publication/309772611_6th_International_Conference_on_Cartography_and_GIS |pages=334–342 }}

[[Category:Geodesy]]