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

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\page constructing_meshes_page Constructing meshes

\n Construction of a mesh consists of:
<ul>
<li>Selecting a geometrical object for meshing</li>
<li>Applying \subpage basic_meshing_algos_page "meshing algorithms" and
\subpage about_hypo_page "hypotheses" which will be used at computation of
this mesh.</li>
</ul>

<em>To construct a mesh:</em>
<ol>
<li>In the \b Mesh menu select <b>Create Mesh</b> or click <em>"Create
Mesh"</em> button in the toolbar. 

\image html image32.png
<center><em>"Create Mesh" button</em></center>

The following dialog box will appear: 

\image html createmesh-inv.png
</li>
<li>For example, you need to mesh a 3d object.
\n First, type the name for your mesh in the "Name" box, by default,
it is "Mesh_1". Then select the object you wish to mesh in the Object
Browser and click the "Add" button.

\image html image120.png
<center><em>"Add" button</em></center>

Now you can define 1d Algorithm and 1d Hypotheses, which will be
applied to the edges of your object. (Note that any object has edges,
even if their existence is not apparent, for example, a sphere has 4
edges). Click the <em>"Add Hypothesis"</em>  button to add a hypothesis.

\image html image121.png
<center><em>"Add Hypothesis" button</em></center>

Click the <em>"Edit Hypothesis"</em> button to define values for the
current hypothesis.

\image html image122.png
<center><em>"Edit Hypothesis" button</em></center>

The use of additional hypotheses is optional (i.e. you may leave
"None" in this box).

Proceed in the same way with 2d and 3d Algorithms and Hypotheses, note
that the choice of hypotheses depends on the algorithm. There must be
one Algorithm and one or several Hypotheses for each dimension of your
object, otherwise you will not get any mesh at all. Of course, if you
wish to mesh a face, which is a 2d object, you don't need to define 3d
Algorithm and Hypotheses.
\n In the <b>Object Browser</b> the structure of the new mesh will be
displayed as follows:

\image html image88.jpg

It contains:
<ul>
<li>a reference to the geometrical object on the basis of which the mesh has been constructed;</li>
<li><b>Applied hypotheses</b> folder containing the references to the
hypotheses applied to the construction of the mesh;</li>
<li><b>Applied algorithms</b> folder containing the references to the
algorithms applied to the construction of the mesh.</li>
</ul>

There is an alternative way to create a mesh on an object simply by
clicking <b>Assign a set of hypotheses</b> button and selecting between
Automatic Tetrahedralization or Hexahedralization.  The program will
automatically generate a 3D mesh with the most appropriate
settings. In the same way you can apply this functionality for meshing
2D objects, in which case 3D algorithms are not applied.</li>

\anchor preview_mesh_anchor

<li> After the mesh object is created and all hypotheses are assigned and
before the mesh computation, it is possible to see the mesh preview.

For this, select the mesh in the Object Browser. From the \b Mesh menu
select \b Preview or click "Preview" button in the
toolbar or activate "Preview" item from the pop-up menu.

\image html mesh_precompute.png
<center><em>"Preview" button</em></center>

Select <b>1D mesh</b> or <b>2D mesh</b> preview mode in the Preview dialog. 


\image html preview_mesh_1D.png "1D mesh preview shows nodes computed on geometry edges"

\image html preview_mesh_2D.png "2D mesh preview shows edge mesh elements, computed on geometry faces"

<b>Compute</b> button computes the whole mesh.

When the Preview dialog is closed, the question about the storage of temporarily
created mesh elements appers:

\image html preview_tmp_data.png

These elenents can be reused in the next mesh computation.
</li>


<li>It is equally possible to skip the Preview and \b Compute the mesh
after the hypotheses are assigned. For this, select your mesh in the <b>Object
Browser</b>. From the \b Mesh menu select \b Compute or click "Compute" button of the
toolbar. 

\image html image28.png
<center><em>"Compute" button</em></center>

The Mesh Computation information box appears.

\image html meshcomputationsucceed.png

If the mesh computation failed, the information about the cause of the
failure is provided.

\image html meshcomputationfail.png

After you select the error, <b>Show Subshape</b> button allows
visualizing the geometrical entity that causes it.

\image html failed_computation.png "Example of the invalid input mesh"

\Note Mesh Computation Information box does not appear if you set
"Mesh computation/Show a computation result notification" preference 
to the "Never" value. This option gives the possibility to control mesh
computation reporting. There are the following possibilities: always
show information box, only if an error occurs or never. 
By default, the information box is always shown after mesh computation operation.

<b>Publish Subshape</b> button publishes the subshape, whose meshing
failed, in GEOM component as a child of the mesh geometry, which
allows analyzing the problem geometry and creating a submesh on it in
order to locally tune hypotheses.

<b>NOTE</b> It is possible to define a 1D or a 2D mesh in a
python script and then use such submeshes in the construction of a 3D
mesh. For this, there exist two algorithms: <b>Use existing edges</b> and <b>Use
existing faces</b>. They are not entirely usable from the GUI, so a
mesh created using these algorithms should be exported into a python
script, edited and then imported into the GUi. 

Consider trying a sample script for construction of a mesh from our 
\ref tui_creating_meshes_page "TUI Scripts" section.
</li>
</ol>

*/