Some UK Ordnance Survey coordinate conversions in pure Ruby.

WGS84 lat/lons -> OSGB36 lat/lons-> OS Eastings & Northings 

A tidied-into-a-module-and-gem tweak of Harry Wood's port of Chris Veness' 
http://www.movable-type.co.uk/scripts/latlong-convert-coords.html


Originally ported to Ruby by Harry Wood:
http://www.harrywood.co.uk/blog/2010/06/29/ruby-code-for-converting-to-uk-ordnance-survey-coordinate-systems-from-wgs84/

(c) Chris Veness 2005-2010, (c) Harry Wood 2010-2011
Teeny portions (c) Matt Patterson 2011

Released under an LGPL license
http://www.fsf.org/licensing/licenses/lgpl.html


Examples:

WGS84 lat/lon:

lon = -0.10322
lat = 51.52237
height = 0

wgs84_point = OsgbConvert::WGS84.new(lat, lon, height)


osgb36_point = wgs84_point.osgb36

osUKgridPoint = OsgbConvert::OSGrid.from_osgb36(osgb36_point)
# alternatively
osUKgridPoint = OsgbConvert::OSGrid.from_wgs84(wgs84_point)
easting  = osUKgridPoint.easting
northing = osUKgridPoint.northing

gridrefLetters = osUKgridPoint.grid_ref(8) # 8 is also the default so osUKgridPoint.grid_ref would work just as well

puts "wgs84 lat: #{wgs84_point.lat}, wgs84 lon: #{wgs84_point.long}"
puts "http://www.openstreetmap.org/?mlat=#{wgs84_point.lat}&mlon=#{wgs84_point.long}&zoom=16"
puts "osgb36 lat: #{osgb36_point.lat}, osgb36 lon: #{osgb36_point.long}"
puts "easting: #{osUKgridPoint.easting}, northing: #{osUKgridPoint.northing}. As a grid ref: #{osUKgridPoint.grid_ref}"
puts "http://streetmap.co.uk/grid/#{osUKgridPoint.easting}_#{osUKgridPoint.northing}_106"