/*!

\page merging_nodes_page Merging nodes

This functionality allows user to detect groups of coincident nodes
with specified tolerance; each group of the coincident nodes can be
then converted to the single node.

\image html mergenodes_ico.png "Merge nodes menu button"

<em>To merge nodes of your mesh:</em>
<ol>
<li>Choose \b Modification -> \b Transformation -> <b>Merge nodes</b>
  menu item. The following dialog box shall appear:</li>
<br>
\image html mergenodes_auto.png
<br>
<ul>
<li>\b Name is the name of the mesh whose nodes will be merged.</li>
<li>\b Automatic or \b Manual mode allows choosing how the nodes are
processed.
<li>\b Tolerance is a maximum distance between nodes sufficient for
merging.</li>
<li>Activation of <b>No merge of corner and medium nodes of quadratic
    cells</b> check-box prevents merging medium nodes of quadratic
    elements with corner nodes. This check-box is enabled provided
    that the selected mesh includes quadratic elements.</li>
<li><b>Exclude Groups</b> group box allows to ignore the nodes which
belong to the specified mesh groups.</li>
<li><b>Nodes to keep</b> group box allows to specify nodes to keep in
  the mesh. (By default a node being the first in a group of
  coincident nodes is kept.) It is possible to either select nodes in
  the Viewer or select groups of any element type whose nodes will be
  kept.
  <ol>
    <li>\a Selection button activates selection of nodes to keep.</li>
    <li><b>Node IDs</b> button activates selection of nodes in the
      Viewer.</li>
    <li><b>Groups and Sub-meshes</b> button activates selection of
      groups and sub-meshes.</li>
    <li>\b Add button adds selected nodes or groups to the list.</li>
    <li> Nodes or groups selected in the list can be removed using \b
      Remove button.</li>
  </ol>
</li>
</ul>

<li><b>Automatic mode:</b>
<br>
<ul>
<li>In the \b Automatic Mode all Nodes within the indicated tolerance
will be merged. The nodes which belong to the groups specified in the
<b>Exclude Groups</b> will be not taken into account.</li>
</ul>
</li><br>
<li> The \b Manual mode gives you full control of what the operation will do.
In this mode additional controls are available:
<ul>
<li>\b Detect button generates the list of coincident nodes for the given
\b Tolerance.</li>
<li><b>Coincident nodes</b> is a list of groups of nodes for
  merging. After the operation all nodes of each group will
  be united into one node. The first node of a group is kept and
  the others are removed.
<ul>
<li>\b Remove button deletes the selected group from the list.</li>
<li>\b Add button adds to the list a group of nodes selected in the
viewer with pressed "Shift" key.</li>
<li><b>Select all</b> check-box selects all groups.</li>
<li><b>Show double nodes IDs</b> check-box shows/hides identifiers of
nodes of selected groups in the 3D viewer.</li>
</ul>

<br>
\image html mergenodes.png
<br>
</li>
<li><b>Edit selected group</b> list allows editing the selected
  group:
  <br><br>
  \image html add.png
  <center>adds to the group the nodes selected in the viewer.</center>
  <br>
  \image html remove.png
  <center>removes from the group the selected nodes.</center>
  <br>
  \image html sort.png
  <center>moves the selected node to the first position in the
    group in order to keep it in the mesh.</center><br>
</li>
</ul>
</li>
<li>To confirm your choice click \b Apply or <b>Apply and Close</b> button.</li>
</ol>

\image html merging_nodes1.png "The initial object"

\image html merging_nodes2.png "The object has been merged"

<br><b>See Also</b> a sample TUI Script of a 
\ref tui_merging_nodes "Merge Nodes" operation.  

*/