\page cutting_quadrangles_page Cutting quadrangles
-\n This operation allows to cut one or several quadrangle elements by
-addition of a supplementary edge which will connect two opposite
-corners.
+This operation allows cutting one or several quadrangle elements into two or four triangles.
<em>To cut quadrangles:</em>
-<ol>
-<li>Display a mesh or a sub-mesh in the 3D viewer.</li>
-<li>In the \b Modification menu select the <b>Cutting of quadrangles</b> item or
+
+1) Select a mesh (and display it in the 3D Viewer if you are going to pick elements by mouse).
+
+2) In the \b Modification menu select the <b>Cutting of quadrangles</b> item or
click <em>"Cutting of quadrangles"</em> button in the toolbar.
\image html image82.png
\image html a-cuttingofquadrangles.png
-\par
-<ul>
-<li>The main list contains the list of quadrangles. You can click on
-an quadrangle in the 3D viewer and it will be highlighted (lock Shift
-keyboard button to select several quadrangles). Click \b Add button and
-the ID of this quadrangle will be added to the list. To remove a
-selected element or elements from the list click \b Remove button. <b>Sort
-list</b> button allows to sort the list of IDs. \b Filter button allows to
-apply a definite filter to the selection of quadrangles.</li>
-<li><b>Apply to all</b> check box allows to modify the orientation of all
-quadrangles of the currently displayed mesh or sub-mesh.</li>
-<li>\b Preview - provides a preview of cutting in the viewer.</li>
-</ul>
-
-<ul>
-<li>\b Criterion
-<ul>
-<li><b>Use diagonal 1-3</b> and <b>Use diagonal 2-4</b> allows to
-specify the opposite corners which will be connected by the cutting
-edge.</li>
-<li><b>Use numeric functor</b> - allows to choose a quality criterion
- which will be optimized at the outcome of the operation.
-<ul>
-<li><b>Minimum diagonal</b> - cuts by the shortest edge.</li>
-<li><b>Aspect Ratio</b> - cuts by the edge splitting the quadrangle
-into triangles with optimal \ref aspect_ratio_page "Aspect Ratio". The reference value is 1.</li>
-<li><b>Minimum Angle</b> - cuts by the edge splitting the quadrangle
-into triangles with optimal \ref minimum_angle_page "Minimum Angle". The reference value is 60 degrees.</li>
-<li><b>Skew</b> - cuts by the edge splitting the quadrangle
-into triangles with optimal \ref skew_page "Skew". The reference value
-is 0.0 degrees.</li>
-</ul>
-</li>
-</ul>
-</li>
-<li><b>Select from</b> - allows to choose a sub-mesh or an existing
-group whose quadrangle elements will be automatically added to the
-list.</li>
-</ul>
-</li>
-<li>Click the \b Apply or <b>Apply and Close</b> button to confirm the operation.</li>
-</ol>
+- The main list contains the list of quadrangles selected for cutting. You can
+click on a quadrangle in the 3D viewer and it will be highlighted (lock Shift
+keyboard button to select several quadrangles):
+ - Click \b Add button and the ID of this quadrangle will be added to the list.
+ - To remove a selected element or elements from the list click \b Remove button.
+ - <b>Sort list</b> button allows sorting the list of IDs.
+ - \b Filter button allows applying a definite \ref filtering_elements "filter"
+ to the selection of quadrangles.
+- <b>Apply to all</b> check box allows cutting all quadrangles of the selected mesh.
+- \b Preview provides a preview of cutting in the viewer. It is disabled for <b>Cut into 4 triangles</b> as this cutting way implies no ambiguity.
+- \b Criterion defines the way of cutting:
+ - <b>Cut into 4 triangles</b> allows cutting a quadrangle into four triangles by inserting a new node at the center of the quadrangle. The other options allow cutting a quadrangle into two triangles by connecting the nodes of a diagonal.
+ - <b>Use diagonal 1-3</b> and <b>Use diagonal 2-4</b> allow specifying the opposite corners, which will be connected to form two new triangles.
+ - <b>Use numeric functor</b> allows selecting in the field below a quality metric, which will be optimized when choosing a diagonal for cutting a quadrangle:
+ - <b>Minimum diagonal</b> cuts by the shortest diagonal.
+ - <b>Aspect Ratio</b> cuts by the diagonal splitting the quadrangle into triangles with \ref aspect_ratio_page "Aspect Ratio" closer to 1
+ - <b>Minimum Angle</b> cuts by the diagonal splitting the quadrangle into triangles with \ref minimum_angle_page "Minimum Angle" closer to 60 degrees.
+ - <b>Skew</b> cuts by the diagonal splitting the quadrangle into triangles with \ref skew_page "Skew" closer to 0.0 degrees.
+- <b>Select from</b> allows choosing a sub-mesh or an existing group, whose quadrangle elements then can be added to the main list.
+
+3) Click the \b Apply or <b>Apply and Close</b> button to confirm the operation.
\image html image52.jpg "The chosen quadrangular element"
