smesh/doc/gui/input/cutting_quadrangles.rst

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.. _cutting_quadrangles_page:
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Cutting quadrangles
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This operation allows cutting one or several quadrangle elements into two or four triangles.
*To cut quadrangles:*
.. |img| image:: ../images/image82.png
#. Select a mesh (and display it in the 3D Viewer if you are going to pick elements by mouse).
#. In the **Modification** menu select the **Cutting of quadrangles** item or click *"Cutting of quadrangles"* button |img| in the toolbar.
The following dialog box will appear:
.. image:: ../images/a-cuttingofquadrangles.png
:align: center
* 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 **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 **Remove** button.
* **Sort list** button allows sorting the list of IDs.
* **Filter** button allows applying a definite :ref:`filter <filtering_elements>` to the selection of quadrangles.
* **Apply to all** check box allows cutting all quadrangles of the selected mesh.
* **Preview** provides a preview of cutting in the viewer. It is disabled for **Cut into 4 triangles** as this cutting way implies no ambiguity.
* **Criterion** defines the way of cutting:
* **Cut into 4 triangles** 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.
* **Use diagonal 1-3** and **Use diagonal 2-4** allow specifying the opposite corners, which will be connected to form two new triangles.
* **Use numeric functor** allows selecting in the field below a quality metric, which will be optimized when choosing a diagonal for cutting a quadrangle:
* **Minimum diagonal** cuts by the shortest diagonal.
* **Aspect Ratio** cuts by the diagonal splitting the quadrangle into triangles with :ref:`Aspect Ratio <aspect_ratio_page>` closer to 1
* **Minimum Angle** cuts by the diagonal splitting the quadrangle into triangles with :ref:`Minimum Angle <minimum_angle_page>` closer to 60 degrees.
* **Skew** cuts by the diagonal splitting the quadrangle into triangles with :ref:`Skew <skew_page>` closer to 0.0 degrees.
* **Select from** allows choosing a sub-mesh or an existing group, whose quadrangle elements then can be added to the main list.
#. Click the **Apply** or **Apply and Close** button to confirm the operation.
.. image:: ../images/image52.jpg
:align: center
.. centered::
The chosen quadrangular element
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.. image:: ../images/image51.jpg
:align: center
.. centered::
Two resulting triangular elements
**See Also** a sample TUI Script of a :ref:`tui_cutting_quadrangles` operation.