smesh/doc/salome/gui/SMESH/input/grouping_elements.doc

/*!

\page grouping_elements_page Grouping elements

In Mesh module it is possible to create groups of mesh entities:
nodes, edges, faces, volumes, 0D elements or balls. One group contains
elements of only one type. Groups, unlike sub-meshes, are exported
along with mesh entities into the files of following formats: MED, UNV,
and CGNS. The group has a color attribute which is used for
visualization only and is not exported.

There are three types of groups different by their internal
organization:<ol>
<li><b>Standalone group</b> is a static set of mesh entities. Its
  contents can be explicitly controlled by the user. Upon removal of
  the entities included into the group, the group becomes empty and
  its content can be restored only manually. Hence it is
  reasonable to create standalone groups when the mesh generation is
  finished and mesh quality is verified.
  \warning Creation and edition of large standalone groups in
  \ref creating_groups_page "Create group" dialog using manual edition
  is problematic due to poor performance of the dialog.</li>
  
<li><b>Group on geometry</b> is associated to a sub-shape or a group of
  sub-shapes of the main shape and includes mesh entities generated on
  these geometrical entities. The association to a geometry is
  established at group construction and cannot be changed. The group
  contents are always updated automatically, hence the
  group can be created even before mesh elements generation.</li>
<li><b>Group on filter</b> encapsulates a filter, which is used to
  select mesh entities composing the group from the whole
  mesh. Criteria of the filter can be changed at any time. The
  group contents are always updated automatically, hence
  the group can be created even before mesh elements generation.</li>
</ol>
The group on geometry and group on filter can be converted to
a standalone group.

\image html groups_in_OB.png "Groups of different types look differently in the Object Browser"

The following ways of group creation are possible:

- \subpage creating_groups_page "Create group" dialog allows creation of
  a group of any type:
  \ref standalone_group "Standalone group",
  \ref group_on_geom "Group on geometry" and
  \ref group_on_filter "Group on filter" using dedicated tabs.
- \subpage create_groups_from_geometry_page "Create Groups from Geometry"
  dialog allows creation of several groups on geometry at once.
- Standalone groups of all nodes and elements of the chosen sub-mesh
  (type of elements depends on dimension of sub-mesh geometry) can
  be created using <b>Mesh -> Construct Group</b> menu item (available
  from the context menu as well).
- Standalone groups of any element type can be created basing on nodes
  of other groups - using \subpage group_of_underlying_elements_page
  "Group based on nodes of other groups" dialog.
- Standalone groups can be created by applying 
  \subpage using_operations_on_groups_page "Boolean operations" to
  other groups.
- Creation of standalone groups is an option of many 
  \ref modifying_meshes_page "mesh modification" operations.

The created groups can be later:

- \subpage editing_groups_page "Edited"
- \subpage deleting_groups_page "Deleted", either as an object or
  together with contained elements.
- The group on geometry and group on filter can be 
  \ref convert_to_standalone "converted into the standalone" group.
- \ref importing_exporting_meshes_page "Exported" into a file as a
  whole mesh.

In the Object Browser, if an item contains more than one child group,
it is possible to sort the groups by name in ascending order
using <b>Sort children</b> context menu item. 

\image html smesh_sort_groups.png "Sorting groups"

An important tool, providing filters for creation of standalone
groups and groups on filter is \ref selection_filter_library_page.

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