Coordinate tools and resources

Our guide to coordinate systems in Great Britain acts as the user manual for some of the calculations you can perform using the spreadsheet. It explains the limitations of the type of datum transformation included in the spreadsheet, which you should bear in mind. If you need transformation accuracy better than the 3 metres, you should use OSTN15 and OSGM15 instead of the simple transformation in the spreadsheet.

Scale factors, convergence and t-T are included in the spreadsheet but are not covered in the guide.

Read our guide to coordinate systems in Great Britain (PDF)

You can carry out common calculations with our coordinate calculations spreadsheet. It includes a full set of Transverse Mercator projection functions, so you can easily:

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

• Compute local scale factor and grid convergence at any point on the grid, and compute 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.

• Perform simple ("Helmert" style) coordinate transformations. E.g. between WGS84 and OSGB36 with an accuracy of about 3 metres.

• Reformat latitude and longitude coordinates between:

• Degrees, minutes and seconds.

• Decimal degrees.

• Degrees and decimal minute formats.

Access the coordinate calculations spreadsheet (xls)

The map reference conversion spreadsheet will help convert between full national grid references and map tile references that use the 100km square letters.

Access the map reference conversion spreadsheet (xlsm) 

• Use the raw dataset from the Developer pack. This includes the grid of transformation parameters, the procedures/equations to use, a worked example and some sample files for testing. Technical information is also included.
  Access the Developer pack (ZIP, 13MB)

• The Lite Developer pack is a reduced density version of OSTN15 and OSGM15 on a 20km grid. Lower accuracy (0.08m horizontal RMS tested against full version) from a much more compact parameter set.
  Access the OSTN15_OSGM15 Lite Developer pack (ZIP, 70KB)

• NTv2 is popular with many GIS systems. The zip archive contains both text and binary NTv2 format files for OSTN15, sample files for testing and a user guide. Access NTv2 format files (ZIP, 28MB) 

• OSGM15 geoid model data in GTX format. Access the OSGM15 GTX format (ZIP, 2MB)