NoMethodError: Undefined method 'deg2rad' for #<Class:0x0000>

gistfile1.rb

class Listing < ActiveRecord::Base
  set_table_name :Listing
  
  scope :near, lambda{
                        |*args|
                        origin = *args.first[:origin]
                        if (origin).is_a?(Array)
                          origin_lat, origin_lng = origin
                        else
                          origin_lat, origin_lng = origin.latitude, origin.longitude
                        end
                        origin_lat, origin_lng = deg2rad(origin_lat), deg2rad(origin_lng)
                        within = *args.first[:within]
                        {
                          :conditions => %(
                            (ACOS(COS(#{origin_lat})*COS(#{origin_lng})*COS(RADIANS(Listing.lat))*COS(RADIANS(Listing.lng))+
                            COS(#{origin_lat})*SIN(#{origin_lng})*COS(RADIANS(Listing.lat))*SIN(RADIANS(Listing.lng))+
                            SIN(#{origin_lat})*SIN(RADIANS(Listing.lat)))*3963) <= #{within}
                          ),
                          :select => %( Listing.*,
                            (ACOS(COS(#{origin_lat})*COS(#{origin_lng})*COS(RADIANS(Listing.lat))*COS(RADIANS(Listing.lng))+
                            COS(#{origin_lat})*SIN(#{origin_lng})*COS(RADIANS(Listing.lat))*SIN(RADIANS(Listing.lng))+
                            SIN(#{origin_lat})*SIN(RADIANS(Listing.lat)))*3963) AS distance
                          )
                        }
                      }
    protected           
    def deg2rad(degrees)
           degrees.to_f / 180.0 * Math::PI
    end
    
end