eturns the const pointer
to the start point vertex of the edge.<br>
If the edge is infinite in that direction returns NULL. </td>
          </tr>
          <tr>
            <td style="font-family: Courier New,Courier,monospace;">void
            <span style="font-weight: bold;">vertex0</span>(voronoi_vertex_type*
v) </td>
            <td>Sets the start point
pointer of the edge. </td>
          </tr>
          <tr>
            <td style="font-family: Courier New,Courier,monospace;">voronoi_vertex_type*
    