How do I change my coordinates in Latitude and Longitude to grid Eastings and Northings or vice versa?
A. You must first determine if you require a conversion or a transformation, i.e. are your coordinate systems based on the same datum. If you wish to convert GPS derived coordinates (based on the WGS84 or ETRS89 ellipsoid) to Ordnance Survey National Grid coordinates (based on the Airy 1830 ellipsoid) or vice versa, then you require a transformation. The Coordinate Converter facility (available from the GPS Website homepage) will perform this operation on either a single position or using a batch file for multiple coordinate input. You have to register to use this facility. If you wish to convert the format of your coordinates from Latitudes and Longitudes to grid Eastings and Northings on the same datum then you can use the spreadsheet available here. For more information on datums and coordinate systems see the online guide available here.
