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
[edit]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 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.[1] 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.[1]
Airy Modified 1849
[edit]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.[2]
See also
[edit]References
[edit]- 1 2 "Airy 1830 - EPSG:7001". epsg.io.
- ↑ "Airy Modified 1849 - EPSG:7002". epsg.io.
Further reading
[edit]- Airy, George Biddell (1826). "XXXIII. On the figure of the earth". Philosophical Transactions of the Royal Society of London. 116: 548–578.
- Lapaine, Miljenko (2016). "George Biddell Airy and his Contribution to Map Projections Theory". In Bandrova, Temenoujka; Konečný, Milan (eds.). 6th International Conference on Cargography and GIS. Bulgarian Cartographic Association. pp. 334–342.