+ belongs_to :user
+ has_many :tags, :class_name => 'Tracetag', :foreign_key => 'gpx_id', :dependent => :delete_all
+ has_many :points, :class_name => 'Tracepoint', :foreign_key => 'gpx_id', :dependent => :delete_all
+
+ scope :visible, where(:visible => true)
+ scope :visible_to, lambda { |u| visible.where("visibility IN ('public', 'identifiable') OR user_id = ?", u) }
+ scope :public, where(:visibility => ["public", "identifiable"])
+