Ruby implementation for GMercatorProjection

Mercator.rb

# This is a port of the javascript code found in the following link
#http://groups.google.com/group/Google-Maps-API/browse_thread/thread/a45947d72c27cc73

class Mercator
  #offset is defined at zoom level 21 which means that this Mercator is valid for 21 zoom levels
  OFFSET = 268435456
  RADIUS = OFFSET / Math::PI
  
  def self.lng_to_x(lng, zoom)
    (OFFSET + RADIUS * lng * Math::PI / 180).to_i >> (21 - zoom)
  end
  
  def self.lat_to_y(lat, zoom)
    (OFFSET-RADIUS*Math.log((1+Math.sin(lat*Math::PI/180))/(1-Math.sin(lat*Math::PI/180)))/2).to_i >> (21 - zoom)
  end

  def self.x_to_lng(x, zoom)
    (((x<<(21 - zoom))-OFFSET)/RADIUS)*180/Math::PI
  end
  
  def self.y_to_lat(y, zoom)
    (Math::PI/2-2*Math.atan(Math.exp(((y<< (21 - zoom))-OFFSET)/RADIUS)))*180/Math::PI
  end
end