/*!

\page revolution_page Revolution

\n Revolution is used to build mesh elements of plus one
dimension than the input ones.  Boundary elements around generated
mesh of plus one dimension are additionally created. All created
elements can be automatically grouped. Revolution can be used to create
a \ref extrusion_struct "structured mesh from scratch". 
See \ref extrusion_page page for general information on Revolution,
which can be viewed as extrusion along a circular path.

<em>To apply revolution:</em>
<ol>
  <li>From the \b Modification menu choose the \b Revolution item or click
    <em>"Revolution"</em> button in the toolbar.

\image html image92.png
<center><em>"Revolution" button</em></center>

The following dialog will appear:

\image html revolution1.png

  </li>

  <li>In this dialog:
    <ul>
    <li>Use \a Selection button to specify what you are going to
    select at a given moment, \b Nodes, \b Edges or \b Faces.
\image html image120.png
<center><em>"Selection" button</em></center>
    </li>
    <li>Specify \b Nodes, \b Edges and \b Faces, which will be revolved, by one
      of following means:
      <ul>
        <li><b>Select the whole mesh, sub-mesh or group</b> activating this
          check-box.</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>Node IDs</b>, <b>Edge
            IDs</b> and <b>Face IDs</b> fields. The selected elements will
          be highlighted in the viewer, if the mesh is shown there.</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>Specify the \b Axis of revolution:
      <ul>
        <li>Specify the coordinates of the start \b Point of the
          axis of revolution; either directly or by picking a node
          in the Viewer (selection of nodes is activated as you click
          the \a Selection button).</li>
        <li>Specify the \b Vector of the axis in either of three ways:
          <ul>
            <li>directly adjust vector components;</li>
            <li>click \a Selection button, choose <em>From Origin to
                selected Point</em> in the opened menu and pick a node
                in the Viewer; </li>
            <li>click \a Selection button, chose <em>Normal to
                selected Face</em> in the opened menu and pick a mesh
                face in the Viewer.</li> 
      </ul></ul>
    </li>
    <li>Specify the \b Angle of revolution and the <b>Number of
        steps </b> of revolution,
      <ul> 
        <li> <b>Angle by Step</b> - the elements are revolved by the
          specified angle at each step (i.e. for Angle=30 and Number of
          Steps=3, the elements will be extruded by 30 degrees twice for a
          total of 30*3=90)
\image html revolutionsn2.png "Example of Revolution with Angle by Step. Angle=30 and Number of Steps=3"
        </li>
        <li> <b>Total Angle</b> - the elements are revolved by the
          specified angle only once and the number of steps defines the
          number of iterations (i.e. for Angle=30 and Number of Steps=3,
          the elements will be revolved by 30/3=10 degrees twice for a
          total of 30).
\image html revolutionsn1.png "Example of Revolution with Total Angle. Angle=30 and Number of Steps=3"
        </li>
      </ul>
    </li>
    <li>Specify the \b Tolerance, which is used to detect nodes lying
      on the axis of revolution.
    </li>
    <li>Activate  <b>Preview</b> check-box to see the result mesh in
      the viewer.
    </li>
    <li>If you activate <b>Generate Groups</b> check-box, the <em>result elements</em>
      created from <em>selected elements</em> contained in groups will be
      included into new groups named by pattern "<old group
      name>_rotated" and "<old group name>_top". For example if a
      selected quadrangle is included in \a g_Faces group (see figures
      below) then result hexahedra will be included in \a
      g_Faces_rotated group and a quadrangle created at the "top" of
      revolved mesh will be included in \a g_Faces_top group. <br> 
\image html extrusion_groups.png
\image html extrusion_groups_res.png
    <p> This check-box is active only if there are some groups in the mesh.
    </li>
    </ul>
  </li>

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

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

*/