-<li>select the type of elements which will be extruded (0D, 1D or 2D),</li>
-<li>specify the IDs of the elements which will be extruded:
-<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 filter to the selection of elements. See more
-about filters in the \ref selection_filter_library_page "Selection filter library" page.</li>
-</ul>
-</li>
-<li>If the <b>Extrude to Distance</b> radio button is selected</li>
-<ul>
-<li>specify the distance at which the elements will be extruded,</li>
-</ul>
-<li>If the <b>Extrude Along Vector</b> radio button is selected</li>
-<ul>
-<li>specify the coordinates of the vector along which the elements will be extruded, or select the face (the normal to the face will define the vector)</li>
-<li>specify the distance of extrusion along the vector,</li>
-</ul>
-<li>specify the number of steps;</li>
-<li>activate <b>Generate Groups</b> checkbox if it is necessary to copy the groups of
-elements of the source mesh to the newly created one. </li>
-</li>
+ <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 extruded, by one
+ of following means:
+ <ul>
+ <li><b>Select the whole mesh, sub-mesh or group</b> activating the
+ corresponding 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>If the <b>Extrusion to Distance</b> radio button is selected
+ - specify the translation vector by which the elements will be extruded.
+ </li>
+ <p><br></p>
+
+\image html extrusionalongaline2.png
+
+ <li>If the <b>Extrusion Along Vector</b> radio button is selected
+ <ul>
+ <li>specify the coordinates of the \b Vector along which the elements
+ will be extruded, either directly or by selecting the mesh face (the
+ normal to the face will define the vector),</li>
+ <li>specify the \b Distance of extrusion along the vector (it can
+ be negative).</li>
+ </ul>
+ </li>
+ <p><br></p>
+
+\image html extrusionalongaline3.png
+
+ <li>If the <b>Extrusion By Normal</b> radio button is selected,
+ every node of the selected faces is extruded along the \a average
+ of the \a normal vectors to the faces sharing the node. (Nodes and
+ edges cannot be extruded in this mode.)
+ <ul>
+ <li>Specify the \b Distance of extrusion (it can be negative),</li>
+ <li>Use <b>Along average normal</b> check-box to specify along
+ which vector the distance is measured.
+ <ul>
+ <li>If it is \a activated the distance is measured along the
+ average normal mentioned above. </li>
+ <li>If it is \a deactivated every node is extruded along the
+ average normal till its intersection with a virtual plane obtained
+ by translation of the face sharing the node along its own normal
+ by the \b Distance.</li>
+ </ul>
+ The picture below shows a cross-section of a 2D mesh extruded
+ with <b>Along average normal</b> activated (to the left) and
+ deactivated (to the right).
+
+ \image html extrusionbynormal_alongavgnorm.png "'Along average normal' activated (to the left) and deactivated (to the right)"
+ <p></li>
+
+ <li><b>Use only input elements</b> check-box specifies what
+ elements will be used to compute the average normal.<ul>
+ <li> If it is \a activated only selected faces, among faces
+ sharing the node, are used to compute the average normal at
+ the node. </li>
+ <li>Else all faces sharing the node are used.</li></ul>
+
+ The picture below shows a cross-section of a 2D mesh the upper
+ plane of which is extruded with <b>Use only input elements</b>
+ activated (to the left) and deactivated (to the right).
+
+ \image html extrusionbynormal_useonly.png "'Use only input elements' activated (to the left) and deactivated (to the right)"
+ <p></li>
+ </li>
+ </ul>
+
+ <li>Specify the <b>Number of steps</b>.</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>_extruded" 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_extruded group and a quadrangle created at the "top" of
+ extruded 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>