/*!

\page symmetry_page Symmetry

\n This geometrical operation allows to perform a symmetrical copy of
your mesh or some of its elements.

<em>To create a symmetrical copy:</em>

<ol>
<li>From the \b Modification menu choose \b Transformation -> \b Symmetry item  or click
<em>"Symmetry"</em> button in the toolbar.

\image html symmetry.png "Symmetry button"

One of the following dialogs will appear:

It is possible to mirror a mesh or some of its elements through:
\image html symmetry1.png "a point" <br>
\image html symmetry2.png "an axis" <br>
\image html symmetry3.png "a plane (defined by a point and a normal to the plane)"

</li>

<li>In the dialog:
<ul>
<li>specify the elements for the symmetry operation:

<ul>
<li><b>Select the whole mesh, submesh or group</b> activating this
checkbox; or</li>
<li>choose mesh elements with the mouse in the 3D Viewer. It is
possible to select a whole area with a mouse frame; or</li> 
<li>input the element IDs directly in <b>ID Elements</b> field. The
  selected elements will be highlighted in the viewer; or</li>
<li>apply Filters. <b>Set Filter</b> button allows to apply a 
  \ref filtering_elements "filter" to the selection of elements.</li> 
</ul>
</li>

<li>depending on the nature of the mirror object: 
<ul>
<li>if the mesh is mirrored through a point, specify the coordinates
  of the point, either directly or by picking a mesh node;</li>
<li>if the mesh is mirrored through an axis: 
<ul>
<li>specify the coordinates of the start \b Point of the axis, either
  directly or by picking a mesh node;</li>
<li>specify the components of axis \b Vector, either directly or by
  picking a mesh node, in which case \b Vector is defined as a shift
  between the \b Point and the node;</li>
</ul>
</li>

<li>if the mesh is mirrored through a plane:
<ul>
<li>specify the cooordinates of the \b Point lying on the plane,
  either directly or by picking a mesh node;</li>
<li>specify the components of plane \b Normal, either directly or by
  picking a mesh node, in which case \b Normal is defined as a shift
  between the \b Point and the node.</li>
</ul>
</li>

<li>specify the conditions of symmetry operation:
<ul>
<li>activate <b>Move elements</b> radio button to change the location of
  the selected elements within the current mesh;</li>
<li>activate <b>Copy elements</b> radio button to duplicate the
  selected elements at the new location within the current mesh;</li>
<li>activate <b>Create as new mesh</b> radio button to create a new
  element in a new mesh; the new mesh appears in the Object Browser
  with the default name \a MeshName_mirrored (it is possible to change
  this name in the adjacent box);</li>
<li>activate <b> Copy groups </b> check-box to put new mesh entities
  into new groups if source entities belong to some groups. New
  groups are named by pattern "<old group name>_mirrored".</li>
</ul>
</li>
</ul>
<li>activate <b>Preview</b> check-box to show the result of
  transformation in the viewer;</li>
<li>click \b Apply or <b> Apply and Close</b> button to confirm the
  operation.</li>
</ul>

</ol>

<br><b>See Also</b> a sample TUI Script of a 
\ref tui_symmetry "Symmetry" operation.  

*/