Spreadsheet: 120371d1315243153-latitude-and-longitude-to-eastings-and-northings-projectionandtransformationcalculations
Sheet: Constants

ELLIPSOID AND PROJECTION CONSTANTS
 |  |  |  | ° | ' | " | [NAME] | Rads
Semi-major axis, a | 6377563.396 | True origin latitude, j0 | N | 49 | 0 | 0 | 49 | 0.8552113334772214
Semi-minor axis, b | 6356256.91 | True origin longitude, l0 | W | 2 | 0 | 0 | -2 | -0.03490658503988659
Central Meridan Scale, F0 | 0.9996012717 |  |  |  |  | a for OSGB36 = | 6377563.396
True origin Easting, E0 | 400000 |  |  |  |  | b for OSGB36 = | 6356256.91
True origin Northing, N0 | -100000 |  |  |  |  | a for GRS80 & WGS84 = | 6378137
aF0 | 6375020.480988971 |  |  |  |  | b for GRS80 = | 6356752.3141 | Slight difference in b is due to different flattening values
bF0 | 6353722.490487913 |  |  |  |  | b for WGS84 = | 6356752.3142
 |  |  |  |  | All other parameters same
Projection Notes
1. The constants above are correct for working with the Ordnance Survey National Grid.
If you want to work with OS National Grid, do not change anything in the above box.
2. It is also possible to use this spreadsheet to work with Universal Transverse Mercator (UTM) grids.
The constants that must be entered in the yellow boxes if you want to work with UTM are given in Annex A of
'A Guide to coordinate systems in Great Britain', available from the OS GPS website www.gps.gov.uk.
HELMERT TRANSFORMATION CONSTANTS
 |  |  |  |  |  | ETRS89 (WGS84) to OSGB36
translation parallel to X | -446.448 | metres |  |  |  |  | -446.448
translation parallel to Y | 125.157 | metres |  |  |  |  | 125.157
translation parallel to Z | -542.06 | metres |  |  |  |  | -542.06
scale change | 20.4894 | parts per million |  |  |  |  | 20.4894
rotation about X | -0.1502 | seconds of arc |  |  |  |  | -0.1502
rotation about Y | -0.247 | seconds of arc |  |  |  |  | -0.247
rotation about Z | -0.8421 | seconds of arc |  |  |  |  | -0.8421
 |  |  |  | reverse signs to go from OSGB36 to ETRS89
Transformation Notes
1.  It is very important to understand the limitations of simple datum transformations.
This method does not take account of the local distortions present in coordinate reference frames (TRFs)
This is especially important when one or both of the coordinate systems involved is based on a traditional triangulation network
For instance, transforming between WGS84 GPS coordinates and OSGB36 National Grid will incur transformation errors
of up to five metres, depending on location.
Also, this method cannot convert ellipsoid heights to heights above mean sea level.
For full details on the limitations of the method coded here, see the OS publication 'A guide to coordinate systems in
Great Britain', available free from our GPS Website (www.gps.gov.uk) or OS customer helpline.
2.  The constants in the table above are suitable for transforming from WGS84 GPS coordinates to OSGB36 National Grid.
By changing the constants above, this spreadsheet may be used to convert between any two geodetic datums
Some ellipsoid constants are given in 'A guide to coordinate systems in Great Britain'
Ordnance Survey cannot supply suitable transformation parameters for the geodetic systems of other countries -
please make enquiries for these parameters to the national mapping agencies of the country concerned.