--- /dev/null
+.. _constructing_submeshes_page:
+
+***********************
+Constructing sub-meshes
+***********************
+
+.. contents:: `Table of contents`
+
+What the sub-mesh is for
+########################
+
+By purpose, the sub-mesh is an object used to assign to a sub-shape
+different meshing parameters than those assigned to the main shape.
+
+Structurally, the sub-mesh is a mesh on a certain sub-shape, or a group of
+sub-shapes, possibly generated using different meshing algorithms
+and/or hypotheses than those used to generate the mesh on other
+sub-shapes. Elements generated on a sub-shape can be retrieved without
+explicit creation of a sub-mesh by creating a *Group on Geometry* using
+:ref:`Create Groups from Geometry <create_groups_from_geometry_page>` dialog.
+
+Creation of a sub-mesh allows to control individually meshing of a
+certain sub-shape, thus to get a locally coarser or finer mesh, to get
+elements of different types in the same mesh, etc.
+
+A sub-mesh can be meshed individually. To achieve this, select a
+sub-mesh and either invoke **Compute Sub-mesh** vai the contextual
+menu in the Object Browser or invoke **Mesh > Compute** menu.
+
+.. _submesh_shape_section:
+
+How to get a sub-shape for sub-mesh construction
+################################################
+
+A sub-shape to create a sub-mesh on should be retrieved from the main shape
+in one of the following ways:
+
+* In Geometry module, via **New Entity > Explode** menu.
+* In Geometry module, by creation of a group (**New Entity > Group > Create Group** menu).
+* In Mesh module, by :ref:`selecting a mesh element <subshape_by_mesh_elem>` generated on a sub-shape of interest. This way is accessible if the mesh is already computed.
+* In Mesh module, by clicking **Publish Sub-shape** button in a dialog showing :ref:`meshing errors <meshing_failed_anchor>`.
+
+
+.. _submesh_priority:
+
+How hypotheses are selected among sub-meshes
+############################################
+
+Internally, definition of meshing parameters to apply for
+discretization of a certain sub-shape, for example an edge of a
+compound of solids, starts from searching an algorithm, 1D as for the
+edge. The following sub-shapes are sequentially checked for presence
+of a sub-mesh where 1D algorithm is assigned:
+
+* the **edge** itself
+* **groups of edges** containing the edge, if any
+* **wires** sharing the edge
+* **faces** sharing the edge
+* **groups of faces** sharing the edge, if any
+* **shells** sharing the edge
+* **solids** sharing the edge
+* **groups of solids** sharing the edge, if any
+* the **main shape**
+
+(This sequence of sub-shapes defines the **priority** of sub-meshes. Thus more
+local, i.e. assigned to sub-shape of lower dimension, algorithms and
+hypotheses have higher priority during the search of hypotheses to
+apply.)
+
+As soon as a 1D algorithm is found, the search stops and the same
+sequence of sub-shapes is checked to find the main and additional 1D
+hypotheses, which can be taken into account by the found 1D algorithm.
+
+The multi-dimensional algorithms have a higher priority than
+uni-dimensional ones if they are assigned to sub-meshes of the
+same priority.
+
+If meshing parameters are defined on sub-meshes of the same priority,
+for example, different 1D hypotheses are assigned to two faces sharing
+an edge, the hypothesis assigned to a sub-shape with a lower ID will
+be used for meshing. You can :ref:`change <submesh_order_anchor>` mutual
+priority of such concurrent sub-meshes.
+
+.. _submesh_definition:
+
+How to construct a sub-mesh
+###########################
+
+Construction of a sub-mesh consists of:
+
+* Selecting a mesh which will encapsulate the sub-mesh.
+* Selecting a sub-shape for meshing.
+* Selecting a :ref:`meshing algorithm <basic_meshing_algos_page>` which will be used for discretization of this sub-shape.
+* Creating or selecting one or several :ref:`hypotheses <about_hypo_page>`.
+
+
+*To construct a sub-mesh:*
+
+.. |img| image:: ../images/image33.gif
+
+From the **Mesh** menu select **Create Sub-mesh** or click *"Create Sum-mesh"* button |img| in the toolbar.
+
+The following dialog box will appear:
+
+ .. image:: ../images/createmesh-inv2.png
+ :align: center
+
+It allows to define the **Name**, the parent **Mesh** and the **Geometry** (e.g. a face if the parent mesh has been built on box) of the sub-mesh. You can define meshing algorithms and hypotheses in the same way as in :ref:`Create mesh <constructing_meshes_page>` dialog.
+
+Later you can change the applied hypotheses or their parameters in :ref:`Edit mesh/sub-mesh <editing_meshes_page>` dialog. Mesh entities generated using changed hypotheses are automatically removed.
+
+.. _subshape_by_mesh_elem:
+
+If the parent mesh is already computed, then you can define the **Geometry** by picking mesh elements computed on a sub-shape of interest in the 3D Viewer, i.e. you do not have to extract this sub-shape in Geometry module beforehand. To start element selection, press *Selection* button to the right of **Geometry** label. If this button is already down, then click it to release and then click it again. The following pop-up menu allowing to choose a way of geometry definition will appear.
+
+.. image:: ../images/choose_geom_selection_way.png
+ :align: center
+
+**Direct geometry selection** enables selecting the sub-shape in the Object Browser.
+**Find geometry by mesh element selection** activates the following dialog.
+
+.. image:: ../images/find_geom_by_mesh_elem.png
+ :align: center
+
+In this dialog, **Element Type** defines a kind of element to pick in the Viewer. Instead of picking an element in the Viewer, you can type its ID in **Element ID** field. **Geometry name** field allows defining a name of the sub-shape, with which the sub-shape will appear in the Object Browser (if not yet there).
+
+
+.. _submesh_tree:
+
+Sub-mesh in the Object Browser
+##############################
+
+In the Object Browser the structure of the new sub-mesh will be displayed as follows:
+
+ .. image:: ../images/image10.jpg
+ :align: center
+
+It contains:
+
+* a sub-mesh name (*SubMeshFace1*)
+* a reference to the geometrical object on the basis of which the sub-mesh has been constructed (*Cylindrical Face_1*);
+* *Applied hypotheses* folder containing references to hypotheses assigned to the sub-mesh;
+* *Applied algorithms* folder containing references to algorithms assigned to the sub-mesh.
+
+
+**See Also** a sample TUI Script of a :ref:`tui_construction_submesh` operation.
+
