gistfile1.py

import pyproj

""" This function will take Ordnance Survey (British National Grid) positional data and
    return latitude, longitude in wgs84 used by google maps and others. """
def bng_to_wgs84(Easting, Northing):
    
    # Define two projections, one for the British National Grid and one for WGS84 (Lat/Lon)
    # You can use the full PROJ4 definition or the EPSG identifier (PROJ4 uses a file that matches the two)
    
    #bng = Proj("+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +datum=OSGB36 +units=m +no_defs towgs84='446.448,-125.157,542.060,0.1502,0.2470,0.8421,-20.4894'")
    #wgs84 = Proj('+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs')
    
    bng = pyproj.Proj(init='epsg:27700')
    wgs84 = pyproj.Proj(init='epsg:4326')
    
    lat,lon = pyproj.transform(bng,wgs84,Easting,Northing)
    
    # lat,lon should be now -1.3819797470583639, 54.906163255053869
    # which is 53, Fawcett St, Sunderland:
    # http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=54.906163255053869,-1.3819797470583639
    return lat,lon