/*!

\page reorient_faces_page Reorient faces

\n This operation allows changing orientation of faces two ways.
<ol>
<li> To reorient a set of neighboring faces by defining the desired
  orientation by a vector. <br> Since the direction of face normals in
  the set can be even opposite, it is necessary to specify a control
  face whose normal 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> To reorient faces with relation to adjacent volumes. </li>
</ol>

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

<em>To change 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>

The following dialog box will appear:

<center>
\image html reorient_2d_point.png "First mode: to reorient adjacent faces according to a vector. The control face is found by point."
<br>
\image html reorient_2d_face.png "Second mode: to reorient adjacent faces according to a vector. The control face is explicitly given."
<br>
\image html reorient_2d_volume.png "Third mode: to reorient faces with relation to adjacent volumes."
</center>

<li>In this dialog
<ul>
<li>Specify either of the tree operation modes.</li>
<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 according to vector: <ul>
    <li>Specify the coordinates of the \b Point by which the control face
      will be found or the control \b Face itself. You can easy specify the \b
      Point by either picking a node in the 3D Viewer or selecting a vertex
      in the Object Browser. It is possible to pick the \b Face by mouse in
      the 3D Viewer or enter its ID.</li>
    <li>Set up the \b Direction vector to be compared with the normal of the
      control face. If you pick a node in the 3D Viewer then the \b Direction
      vector will go from the coordinate system origin to the selected node.
      If you pick two nodes (holding Shift button) then the \b Direction vector
      will go from the first to the second node.</li> </ul> </li>
<li>To reorient 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> </li>
</ul>
</li>

<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. 

*/