/*!

\page extrusion_page Extrusion

\n Extrusion is a type of surface meshing by generation from
discretized lines. It is used to build mesh elements of plus one
dimension than the swept ones. Each swept 1D element produces one or
more quadrangles (or triangles if one node of a rotated element lays
on the revolution axis).

<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. 

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

The following dialog box will appear:

\image html extrusionalongaline1.png

\image html extrusionalongaline2.png
</li>

<li>In this dialog box you should select:
<ul>
<li>the type of elements which will be extruded (1D or 2D),</li>
<li>specify the IDs of the elements which will be extruded by
selecting them in the 3D viewer or select the whole mesh or
submesh,</li>
<li>specify the vector along which the elements will be extruded,</li>
<li>number of steps.</li>
</ul>
</li>

<li>Click the \b Apply or \b OK button.</li>
</ol>

\image html image77.jpg

\image html image76.jpg

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

*/