></code>
              defining <code class="computeroutput"><span class="identifier">segment_tag</span></code>
              as type
            </li>
<li class="listitem">
              there must be a specialization of <code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">point_type</span></code>
              to define the underlying point type (even if it does not consist of
              points, it should define this type, to indicat