.svg?alt=media&token=1e8c5cb8-8313-4dee-9a83-897615d7ab1f)
.svg?alt=media&token=52cad126-f5f3-479b-a4fe-3db53f640273)
Datum, ellipsoid and projection information
Shape and size of biaxial ellipsoids used in the UK
| Name | Semi-major axis a (m) | Semi-minor axis b (m) | Associated datums and projections |
|---|---|---|---|
Airy 1830 | 6 377 563.396 | 6 356 256.909[10] | OSGB36, National Grid |
Airy 1830 modified | 6 377 340.189 | 6 356 034.447 | Ireland 65, Irish National Grid |
International 1924 aka Hayford 1909 | 6 378 388.000 | 6 356 911.946 | ED50, UTM |
GRS80 aka WGS84 ellipsoid | 6 378 137.000 | 6 356 752.3141 | WGS84, ITRS, ETRS89. |
The ellipsoid squared eccentricity constant e² is computed from a and b by equation (B1).
Transverse Mercator projections used in the UK
| Projection | Scale factor on central meridian (F₀) | True origin, Φ₀ and λ₀ | Map coordinates of true origin (metres), E₀ and N₀ | Ellipsoid |
|---|---|---|---|---|
National Grid | 0.9996012717 | lat 49° N long 2° W | E 400 000 N -100 000 | Airy 1830 |
Irish National Grid | 1.000035 | lat 53°30′ N long 8° W | E 200 000 N 250 000 | Airy 1830 modified |
UTM zone 29 | 0.9996 | lat 0° long 9° W | E 500 000 N 0 | International 1924 or WGS84 |
UTM zone 30 | 0.9996 | lat 0° long 3° W | E 500 000 N 0 | International 1924 or WGS84 |
UTM zone 31 | 0.9996 | lat 0° long 3° E | E 500 000 N 0 | International 1924 or WGS84 |
EPSG codes for common datums and coordinate operations in GB
Many geographic information systems (GIS) and other methods of handling digital geographic data use unique identifiers - Spatial Reference System Identifier (SRID) - for datums, coordinate systems etc.. See https://en.wikipedia.org/wiki/Spatial_reference_system#Identifier. A commonly used SRID Authority is the EPSG (European Petroleum Survey Group) who maintain an online registry of SRIDs at https://epsg.org/home.html. The table below lists EPSG codes of ellipsoids, datums and coordinate operations in common use in the Great Britain.
| Datum (and associated coord ref system) or operation name | EPSG SRID code |
|---|---|
Airy 1830 ellipsoid | 7001 |
GRS80 ellipsoid | 7019 |
WGS84 ellipsoid | 7030 |
OSGB36 Datum, 2D lat/long | 4277 |
OSGB36 Datum, 2D National Grid | 27700 |
OSGB36 Datum, 3D National Grid + ODN height | 7405 |
ODN Vertical Datum | 5701 |
ETRS89 Datum, 2D lat/long | 4258 |
ETRS89 Datum, 3D lat/long/Height | 4937 |
ETRS89 Datum, 3D XYZ | 4936 |
WGS84 Datum, 2D lat/long | 4326 |
WGS84 Datum, 3D lat/long/Height | 4979 |
WGS84 Datum, 3D XYZ | 4978 |
OSTN15 transformation, native 1km grid | 7953 |
OSTN15 transformation, NTv2 version | 7709 |
OSGM15 transformation, ODN | 7711 |
OSGM15 transformation, Orkney Datum | 7712 |
OSGM15 transformation, “Newlyn offshore” | 7713 |
OSGM15 transformation, Lerwick Datum | 7714 |
OSGM15 transformation, Stornoway Datum | 7715 |
OSGM15 transformation, St. Marys Datum (Scilly Isles) | 7716 |
OSGM15 transformation, Douglas Datum (IoM) | 7717 |
WGS84 < - > OSGB36 Helmert transformation (section 6.6) | 1314 |
ETRS89 lat/long + ODN height compound CRS | 9424 |
ETRS89 lat/long + ODN (Offshore) height compound CRS | 9425 |
ETRS89 lat/long + Orkney height compound CRS | 9426 |
ETRS89 lat/long + Lerwick height compound CRS | 9427 |
ETRS89 lat/long + Stornoway height compound CRS | 9428 |
ETRS89 lat/long + Douglas height compound CRS | 9429 |
ETRS89 lat/long + St. Marys height compound CRS | 9430 |
British Isles height ensemble (approx. MSL height across whole of British Isles) | 1288 |
ETRS89 lat/long + British Isles height ensemble compound CRS | 9542 |
Last updated