OSGB/OSI Converter - Strolling Guides

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Latitude & Longitude to OSGB/OSI Converter

These calculations are for illustration only and no liability can be accepted for any losses however caused.

Based in part on Quick Basic code written by Phil Brady, but using the algorithms from 'A Guide to coordinate systems in Great Britain' Appendix C. These are consistent with the formulae in The Irish Grid - A Description of the Co-ordinate Reference System used in Ireland
OSGB Grid References are corrected to OSGM02™ using the methodologies set out in the developer pack downloadable from the OS site. I have yet to implement the changes to OSI references which are still uncorrected.
Postcodes are derived using the OS Code-Point^® Open data.
To download the PHP Class Library and sample code, click here. This does not include the OSGM02™ corrections and postcoding as these require database support.