# More on Converting British National Grid to Latitude and Longitude

So it turns out the internet is awesome.

After I posted a python script that can be used to convert a .csv of Northings and Eastings in British National Grid to a Latitude and Longitude, several people followed suit and sent through their codes in a variety of other languages.

I've just changed over my website and didn't want to lose the codes, so I've put them all here in one handy place. Hope you find them useful.

# Converting Latitude and Longitude to British National grid

This code reads in a .csv file called LatLon, expecting two columns with headers – Latitude and Longitude (in WGS84, decimal form). If the script is run in the same directory as LatLon.csv, it will spit out a second file called LatLonandBNG.csv, with two additional columns: OSGB36 Eastings and Northings respectively.

For the inverse transform – OSGB36 to WGS84 – please refer to this post, where a you can find the relevant python script, and more details on the algorithms involved.

If you don’t have python, you can find instructions for the bits you need on another of my previous posts.

# Converting British National Grid to Latitude and Longitude II

A few months ago, I wrote a python script to convert British National grid coordinates (OSGB36) to latitude and longitude (WGS84).  A fellow blogger Andrzej Bieniek very kindly pointed out that the algorithm was only accurate to around 100m because of an additional subtlety which I hadn’t taken into account.

I’ll have a quick bash at explaining the reasoning behind this difference,  but if you want to skip to the new version of the code (now accurate to 5m) I’ve posted it at the bottom of the page in all its delicious glory. Alternatively, if you are looking for a similarly accurate script applying the inverse transform – ie. WGS84 lat, lon to OSGB36 Eastings, Northings – you can find it here.

# Converting British National Grid to Latitude and Longitude I

EDIT: Andrzej Bieniek brought to my attention that this version is correct to 100m. For a more accurate script (accurate to 5m) see my new post.

I have recently started to deal with a lot of geographical data in my research and and begun to realise it is difficult to go to long without stumbling across the sticky world of map projections – something I knew almost nothing about a year ago.

There is a nice blog post explaining the background by which I shan’t attempt to reproduce, but explanations aside, I found myself today trying to convert a long list of British National grid coordinates into Latitude and Longitude.