/*!

\page reorient_faces_page Orient faces

\n This operation allows fixing the orientation of a set of faces in
the following ways:
<ul>
<li>The required orientation of a set of neighboring faces can be defined
  by a vector giving the direction of a normal to a certain face. <br>
  Since the direction of face normals in the set can be even opposite,
  it is necessary to specify a \a control face, the normal to which
  will be compared with the vector. This face can be either:
  <ul>
    <li>found by proximity to a given point, or</li> 
    <li>specified explicitly.</li> 
  </ul>
</li>
<li>Alternatively, the faces can be oriented relatively to the adjacent volumes.</li>
</ul>

The orientation of a face is changed by reverting the order of its nodes.

<em>To set orientation of faces:</em>
<ol>
<li>In the \b Modification menu select <b>Reorient faces</b>
  item or click <em>Reorient faces</em> button in the toolbar.

<center>
\image html reorient_faces_face.png
<em>"Reorient faces" button</em>
</center>
</li>

<li>In the "Reorient faces" dialog box

<ul>
<li>Select the \b Object (mesh, sub-mesh or group)
  containing faces to reorient, in the Object Browser or in the 3D
  Viewer.</li>

<li>To reorient by direction of the face normal:
    <ul>
    <li>Specify the coordinates of the \b Point by which the control face
      will be found. You can specify the \b Point by picking a
      node in the 3D Viewer or selecting a vertex in the Object
      Browser.</li>
    <li>Set up the \b Direction vector to be compared with the normal of the
      control face. There are following options: <ul>
        <li>adjust vector components directly;</li>
        <li>select a vertex in the Object Browser or a node in the 3D
          Viewer; their coordinates will define vector components;</li>
        <li> pick two nodes (holding Shift button), the \b Direction vector
          will go from the first to the second node.</li>
      </ul>
    </ul>

<br>
<center>
\image html reorient_2d_point.png "The orientation of adjacent faces is chosen according to a vector. The control face is found by point."
</center>

</li>

<li>In the second mode it is possible to pick the \b Face by mouse in the 3D Viewer or directly input the \b Face ID in the corresponding field.

<center>
\image html reorient_2d_face.png "The orientation of adjacent faces is chosen according to a vector. The control face is explicitly given."
</center>

</li>

<li>In the third mode, the faces can be reoriented according to volumes:
    <ul>
    <li>Select an object (mesh, sub-mesh or group) containing
      reference \b Volumes, in the Object Browser or in the 3D
      Viewer.</li>
    <li>Specify whether face normals should point outside or inside
      the reference volumes using <b>Face normal outside volume</b>
      check-box.</li>
    </ul>

<br>
<center>
\image html reorient_2d_volume.png "The orientation of faces is chosen relatively to adjacent volumes."
</center>

</li>
</ul>

<li>Click the \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_reorient_faces "Reorient faces" operation. 

*/