gistfile1.rb

#    t.column "latitude",  :decimal,               :precision => 10, :scale => 4, :default => 0.0, :null => false
#    t.column "longitude", :decimal,               :precision => 10, :scale => 4, :default => 0.0, :null => false
# def want index on both

  def find_nearby(radius = 10, limit = 10)
    
    distance_sql = <<-SQL_END
    IFNULL(SQRT( ((69.1 * (#{self.latitude} - zips.latitude)) * (69.1 * (#{self.latitude} - zips.latitude))) 
    + ( (53 * (#{self.longitude} - zips.longitude)) * (53 * (#{self.longitude} - zips.longitude)))),0)    
    SQL_END
    
    zips = Zip.find( :all,
              :select => "*, #{distance_sql} as distance",
              :limit => limit,
              :order => "distance ASC",
              :conditions => ["
                zips.longitude      >= (#{self.longitude}  - (#{radius}/(COS(#{self.latitude})))) 
                AND zips.longitude  <= (#{self.longitude}  + (#{radius}/(COS(#{self.latitude}))))
                AND zips.latitude   >= (#{self.latitude}   - (0.0143884892 *  #{radius}))
                AND zips.latitude   <= (#{self.latitude}   + (0.0143884892 *  #{radius}))"])
    
    if zips.length > 0
      return zips
    else
      return [self]
    end

  end