Converting UK Easting / Northing to Latitude / Longitude
Posted 09 Jul 2012 in example and python

Recently I needed to convert a large amount of data between UK Easting / Northing coordinates and Latitude / Longitude. There are web services available that support this conversion but they only permit a few hundred requests / hour, which means it would take weeks to process my quantity of data.

Here is the Python script I developed to perform this conversion quickly with the pyproj module:

from pyproj import Proj, transform

v84 = Proj(proj="latlong",towgs84="0,0,0",ellps="WGS84")
v36 = Proj(proj="latlong", k=0.9996012717, ellps="airy",
        towgs84="446.448,-125.157,542.060,0.1502,0.2470,0.8421,-20.4894")
vgrid = Proj(init="world:bng")


def ENtoLL84(easting, northing):
    """Returns (longitude, latitude) tuple
    """
    vlon36, vlat36 = vgrid(easting, northing, inverse=True)
    return transform(v36, v84, vlon36, vlat36)

def LL84toEN(longitude, latitude):
    """Returns (easting, northing) tuple
    """
    vlon36, vlat36 = transform(v84, v36, longitude, latitude)
    return vgrid(vlon36, vlat36)


if __name__ == '__main__':
    # outputs (-1.839032626389436, 57.558101915938444)
    print ENtoLL84(409731, 852012) 

Source code is available on bitbucket.

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