Convert eastings/northings to latitude/longitude using NetTopologySuite
c#, gis
Solution
This is a very old question but as it still came up in a search after 2 years I felt it's still worth providing an answer that may help others.
If you are able to use it the Ordnance Survey now provide a DLL (and an associated data file), or NTv2 file that can be used to perform the more accurate OSTN15 transformation. These are available under the BSD licence at : OSTN15 and OSGM15 for developers
This conversion will transform your co-ordinates to ETRS89 (approximately equivalent to WGS84 in Europe) and will be more accurate than the OSTN97/7 parameter helmert transformation mentioned in the answer from @codeulike.
Problem
I have a bunch of Eastings/Northings coordinates, using the UTM convention as far as I can tell - so basically, they are cartesian coordinates - that I would like to convert to Latitude and Longitude. Presumably NetTopologySuite can help me with this, but I can't find much documentation on it. Anyone got some pointers to get me started? Edit: The Eastings and Northings turned out to be, specifically, OS Grid Reference Eastings and Northings, the issues and conventions around which are discussed here.