gistfile1.rb

module ZipCodes
  def self.included(base)
    base.extend(ClassMethods)
  end
  
  module ClassMethods
    def find_zip_codes_by_radius(zip, radius)
      zip_code = ZipCode.find_by_zip_code(zip)
      return [] unless zip_code

      radius = radius.to_f
      latitude_miles = 69.172
      longitude_miles = (latitude_miles * Math.cos(zip_code.latitude * (Math::PI/180))).abs
      latitude_degrees = radius/latitude_miles
      longitude_degrees = radius/longitude_miles

      min_latitude = zip_code.latitude - latitude_degrees
      max_latitude = zip_code.latitude + latitude_degrees
      min_longitude = zip_code.longitude - longitude_degrees
      max_longitude = zip_code.longitude + longitude_degrees

      ZipCode.find(:all,
        :select => "zip_code, sqrt( pow(#{latitude_miles} * (latitude-#{zip_code.latitude}),2) + pow(#{longitude_miles} * (longitude-#{zip_code.longitude}),2)) as distance",
        :conditions => "(latitude BETWEEN #{min_latitude} AND #{max_latitude}) AND (longitude BETWEEN #{min_longitude} AND #{max_longitude}) AND sqrt(pow(#{latitude_miles} * (latitude-#{zip_code.latitude}),2) + pow(#{longitude_miles} * (longitude-#{zip_code.longitude}),2)) <= #{radius}",
        :order => "distance").uniq
    end
  end
end