/*!

\page extrusion_page Extrusion

\n Extrusion is used to build mesh elements of plus one
dimension than the input ones. Any node, segment or 2D element can be
extruded. Element of each type extrude into elements of a certain type
as follows:
<table>
<tr><td><b>Extruded element</b></td><td><b> Result elements </b></td></tr>
<tr><td>Node              </td><td> Segments </td></tr>
<tr><td>Segment           </td><td> Quadrilaterals </td></tr>
<tr><td>Triangle          </td><td> Pentahedrons </td></tr>
<tr><td>Quadrilateral     </td><td> Hexahedrons </td></tr>
<tr><td>Polygon           </td><td> Polyhedrons </td></tr>
<tr><td>Hexagonal polygon </td><td> Hexagonal prism </td></tr>
</table>

<em>To use extrusion:</em>
<ol>
<li>From the \b Modification menu choose the \b Extrusion item or click
<em>"Extrusion"</em> button in the toolbar. 

<center>
\image html image91.png
<em>"Extrusion" button</em>
</center>

The following dialog common for line and planar elements will appear:

\image html extrusionalongaline1.png

\image html extrusionalongaline2.png

</li>

<li>In this dialog:
<ul>
  <li>Select the type of elements which will be extruded (0D, 1D or 2D).</li>
  <li>Specify the IDs of the elements which will be extruded by one
    following means:
    <ul>
      <li><b>Select the whole mesh, submesh or group</b> activating this
        checkbox.</li>
      <li>Choose mesh elements with the mouse in the 3D Viewer. It is
        possible to select a whole area with a mouse frame.</li> 
      <li>Input the element IDs directly in <b>ID Elements</b>
        field. The selected elements will be highlighted in the viewer.</li> 
      <li>Apply Filters. <b>Set filter</b> button allows to apply a
        filter to the selection of elements. See more about filters in
        the \ref filtering_elements "Selection filters" page.</li> 
    </ul>
  </li>
  <li>If the <b>Extrude to Distance</b> radio button is selected</li>
  <ul>
    <li>specify the distance at which the elements will be extruded.</li>
  </ul>
  <li>If the <b>Extrude Along Vector</b> radio button is selected</li>
  <ul>
    <li>specify the coordinates of the vector along which the elements
      will be extruded, or select the face (the normal to the face will
      define the vector),</li>
    <li>specify the distance of extrusion along the vector.</li>
  </ul>
  <li>Specify the number of steps.</li>
  <li>If you activate <b>Generate Groups</b> check-box then the created
    elements contained in groups will be included into new groups named
    by pattern "<old group name>_extruded". </li>
</ul>

<li>Click \b Apply or <b> Apply and Close</b>  button to confirm the operation.</li>
</ol>

\image html image77.jpg "The mesh with an edge selected for extrusion"

\image html image76.jpg "The mesh with extruded edge" 

<br><b>See Also</b> a sample TUI Script of an 
\ref tui_extrusion "Extrusion" operation. 

*/