From this page you can download a Microsoft^® Excel 2002 spreadsheet which will carry out common calculations with coordinates. All of the concepts and formulae given in A guide to coordinate systems in Great Britain, which is the user manual for these calculations, are detailed in the spreadsheet. The guide gives some important warnings about the use of its formulae, which you should be aware of. There are also other projection functions such as scale factors, convergence and t-T in the spreadsheet that are not in the guide.

The spreadsheet includes a full set of Transverse Mercator projection functions, which allows you to:

• Convert latitude and longitude to grid eastings and northings for any Transverse Mercator map projection, including the Ordnance Survey National Grid.



• Convert grid eastings and northings to latitude and longitude for any Transverse Mercator map projection, including the Ordnance Survey National Grid.



• Compute local scale factor at any point on the grid, and compute grid convergence, t-T and true azimuth between any pair of points on the grid.



• Convert latitude and longitude coordinates to cartesian XYZ coordinates and vice versa.



• Convert latitude and longitude coordinates in any coordinate system to any other coordinate system. For instance, GPS coordinates may be converted to Ordnance Survey National Grid coordinates with an accuracy of about 5 metres, anywhere in Great Britain. Please read the guide mentioned above to learn about the limitations of this type of datum transformation. For GPS to National Grid conversion requiring better than 5 metre accuracy, you should not use this simple transformation - use OSTN02 and OSGM02.



• Reformat latitude and longitude coordinates between: Degrees, Minutes & Seconds; decimal Degrees; and Degrees & Decimal Minute formats.

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