3 \page constructing_meshes_page Constructing meshes
5 \n Construction of a mesh on some geometry consists of:
7 <li> \ref create_mesh_anchor "Creating of a mesh object"</li>
8 <li> \ref evaluate_anchor "Evaluating mesh size" (optional)</li>
9 <li> \ref preview_anchor "Previewing the mesh" (optional)</li>
10 <li> \ref submesh_order_anchor "Changing sub-mesh priority" (optional)</li>
11 <li> \ref compute_anchor "Computing the mesh"</li>
13 Mesh can be \ref use_existing_anchor "computed using your own meshing algorithms"
17 \anchor create_mesh_anchor
18 <h2>Creation of a mesh object</h2>
19 <em>To construct a mesh:</em>
21 <li>Select a geometrical object for meshing.</li>
22 <li>In the \b Mesh menu select <b>Create Mesh</b> or click <em>"Create
23 Mesh"</em> button in the toolbar.
26 \image html image32.png
27 <em>"Create Mesh" button</em>
30 The following dialog box will appear:
32 \image html createmesh-inv.png
35 <li>Apply \subpage basic_meshing_algos_page "meshing algorithms" and
36 \subpage about_hypo_page "hypotheses" which will be used to compute
39 "Create mesh" dialog box contains several tab pages titled \b 3D,
40 \b 2D, \b 1D and \b 0D. The title of each page reflects the
41 dimension of the CAD model (geometry) the algorithms listed on
42 this page affect and the maximal dimension of elements the algorithms
43 generate. For example, \b 3D page lists the algorithms that affect
44 3D geometrical objects (solids).
47 - Some page(s) can be disabled if the source geometrical
48 object does not include shapes (sub-shapes) of the corresponding
49 dimension(s). For example, if the input object is a geometrical face,
50 \b 3D page is disabled.
51 - Some algorithms affect the geometry of several dimensions,
52 i.e. "1D-2D" or "1D-2D-3D". If such an algorithm is selected by the
53 user, the dialog box pages related to the corresponding lower level
54 dimensions are disabled.
55 - \b 0D page does not refer to the 0D elements, but to 0D
56 geometry (vertices). Mesh module does not provide algorithms that
57 produce 0D elements. Currently \b 0D page provides only one
58 algorithm "Segments around vertex" that allows specyfying the required
59 size of mesh edges about the selected vertex (or vertices).
61 For example, you need to mesh a 3D object.
63 First, type the name of your mesh in the \b Name box, by default,
64 it is "Mesh_1". Then select the geometrical object you wish to
65 mesh in the Object Browser and click "Select" button near \b Geometry
66 field (if the name of the object has not yet appeared in \b Geometry field).
69 \image html image120.png
70 <em>"Select" button</em>
73 Now you can define 3D Algorithm and 3D Hypotheses, which will be
74 applied to the solids of your geometrical object. Click the <em>"Add
75 Hypothesis"</em> button to add a hypothesis.
78 \image html image121.png
79 <em>"Add Hypothesis" button</em>
82 Click the <em>"Edit Hypothesis"</em> button to change the values for the
86 \image html image122.png
87 <em>"Edit Hypothesis" button</em>
90 Most 2D and 3D algorithms can work without hypotheses using some
91 default meshing parameters. Some algorithms does not require any
92 hypothesis. After selection of an algorithm "Hypothesis" field of
93 the dialog can contain:
95 <li> <em>\<Default\></em> if the algorithm can work using default
97 <li> <em>\<None\></em> if the algorithm requires a hypothesis defining
99 <li> Nothing if the algorithm has no parameters to tune.</li>
101 After selection of an algorithm "Add. Hypothesis" field of
102 the dialog can contain:
104 <li> <em>\<None\></em> if the algorithm can be additionally tuned
105 using an additional hypothesis.</li>
106 <li> Nothing if the algorithm has no additional parameters to tune.</li>
109 Proceed in the same way with 2D and 1D Algorithms and Hypotheses that
110 will be used to mesh faces and edges of your geometry. (Note
111 that any object has edges, even if their existence is not
112 apparent, for example, a sphere has 4 edges). Note that the
113 choice of hypotheses and lower dimension algorithms depends on
114 the higher dimension algorithm.
116 Some algorithms generate mesh of several dimensions, while others
117 produce mesh of only one dimension. In the latter case there must
118 be one Algorithm and zero or several
119 Hypotheses for each dimension of your object, otherwise you will
120 not get any mesh at all. Of course, if you wish to mesh a face,
121 which is a 2D object, you do not need to define a 3D Algorithm and
124 In the <b>Object Browser</b> the structure of the new mesh will be
125 displayed as follows:
128 \image html image88.jpg
133 <li>a reference to the geometrical object on the basis of
134 which the mesh has been constructed;</li>
135 <li><b>Applied hypotheses</b> folder containing the references
136 to the hypotheses applied at the construction of the mesh;</li>
137 <li><b>Applied algorithms</b> folder containing the references
138 to the algorithms applied at the construction of the mesh.</li>
141 There is an alternative way to assign Algorithms and Hypotheses by
142 clicking <b>Assign a set of hypotheses</b> button and selecting among
143 pre-defined sets of hypotheses. In addition to the standard
144 sets of hypotheses, it is possible to create custom sets by editing
145 CustomMeshers.xml file located in the home directory. CustomMeshers.xml
146 file must describe sets of hypotheses in the
147 same way as ${SMESH_ROOT_DIR}/share/salome/resources/smesh/StdMeshers.xml
148 file does (sets of hypotheses are enclosed between <hypotheses-set-group>
151 \image html hypo_sets.png
152 List of sets of hypotheses. Tag <em>[custom]</em> is
153 automatically added to the sets defined by the user
157 Consider trying a sample script for construction of a mesh from our
158 \ref tui_creating_meshes_page "TUI Scripts" section.
160 \anchor evaluate_anchor
161 <h2>Evaluating mesh size</h2>
163 After the mesh object is created and all hypotheses are assigned and
164 before \ref compute_anchor "Compute" operation, it is possible to
165 calculate the eventual mesh size. For this, select the mesh in
166 the <b>Object Browser</b> and from the \b Mesh menu select \b
167 Evaluate. The result of evaluation will be displayed in the following
170 \image html mesh_evaluation_succeed.png
172 \anchor preview_anchor
173 <h2>Previewing the mesh</h2>
175 Before \ref compute_anchor "the mesh computation", it is also possible
176 to see the mesh preview.
178 For this, select the mesh in the Object Browser. From the \b Mesh menu
179 select \b Preview or click "Preview" button in the toolbar or activate
180 "Preview" item from the pop-up menu.
183 \image html mesh_precompute.png
184 <em>"Preview" button</em>
187 Select <b>1D mesh</b> or <b>2D mesh</b> preview mode in the Preview dialog.
189 \image html preview_mesh_1D.png "1D mesh preview shows nodes computed on geometry edges"
191 \image html preview_mesh_2D.png "2D mesh preview shows edge mesh elements, computed on geometry faces"
193 <b>Compute</b> button computes the whole mesh.
195 When the Preview dialog is closed, the question about the storage of temporarily
196 created mesh elements appears:
198 \image html preview_tmp_data.png
200 These elements can be kept in the mesh.
203 \anchor submesh_order_anchor
204 <h2>Changing sub-mesh priority</h2>
206 If the mesh contains concurrent \ref constructing_submeshes_page "sub-meshes",
207 it is possible to change the priority of their computation, i.e. to
208 change the priority of applying algorithms to the shared sub-shapes of
211 <em>To change submesh priority:</em>
213 Choose "Change submesh priority" from the Mesh menu or a pop-up
214 menu. The opened dialog shows a list of submeshes in the order of
217 There is an example of submesh order modifications taking a Mesh created on a Box
218 shape. The main Mesh object:
220 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=20</li>
221 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis<b>Max Element Area</b>
224 The first submesh object <b>Submesh_1</b> created on <b>Face_1</b> is:
226 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=4</li>
227 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
229 The second submesh object <b>Submesh_2</b> created on <b>Face_2</b> is:
231 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=8</li>
232 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
235 And the last submesh object <b>Submesh_3</b> created on <b>Face_3</b> is:
237 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=12</li>
238 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
241 The sub-meshes become concurrent if they share sub-shapes that can be
242 meshed with different algorithms (or different hypotheses). In the
243 example, we have three submeshes with concurrent algorithms, because
244 they have different hypotheses.
246 The first mesh computation is made with:
248 \image html mesh_order_123.png
249 <em>"Mesh order SubMesh_1, SubMesh_2, SubMesh_3"</em></center>
251 \image html mesh_order_123_res.png
252 <em>"Result mesh with order SubMesh_1, SubMesh_2, SubMesh_3 "</em></center>
254 The next mesh computation is made with:
256 \image html mesh_order_213.png
257 <em>"Mesh order SubMesh_2, SubMesh_1, SubMesh_3"</em></center>
259 \image html mesh_order_213_res.png
260 <em>"Result mesh with order SubMesh_2, SubMesh_1, SubMesh_3 "</em></center>
262 And the last mesh computation is made with:
264 \image html mesh_order_321.png
265 <em>"Mesh order SubMesh_3, SubMesh_2, SubMesh_1"</em></center>
266 <center>\image html mesh_order_321_res.png
267 <em>"Result mesh with order SubMesh_3, SubMesh_2, SubMesh_1 "</em></center>
269 As we can see, each mesh computation has a different number of result
270 elements and a different mesh discretization on the shared edges (the edges
271 that are shared between <b>Face_1</b>, <b>Face_2</b> and <b>Face_3</b>)
273 Additionally, submesh priority (the order of applied algorithms) can
274 be modified not only in a separate dialog box, but also in
275 the <b>Preview</b>. This helps to preview different mesh results,
276 modifying the order of submeshes.
278 \image html mesh_order_preview.png
279 <em>"Preview with submesh priority list box"</em></center>
281 If there are no concurrent submeshes under the Mesh object, the user
282 will see the following information.
284 \image html mesh_order_no_concurrent.png
285 <em>"No concurrent submeshes detected"</em></center>
288 \anchor compute_anchor
289 <h2>Computing the mesh</h2>
291 It is equally possible to skip \ref evaluate_anchor "the Evaluation"
292 and \ref preview_anchor "the Preview" and to \b Compute the mesh after
293 the hypotheses are assigned. For this, select your mesh in
294 the <b>Object Browser</b>. From the \b Mesh menu select \b Compute or
295 click "Compute" button of the toolbar.
298 \image html image28.png
299 <em>"Compute" button</em>
302 After the mesh computation finishes, the Mesh Computation information
303 box appears. In case of a success, the box shows
304 information on number of entities of different types in the mesh.
306 \image html meshcomputationsucceed.png
308 If the mesh computation failed, the information about the cause of the
309 failure is provided in \b Errors table.
311 \image html meshcomputationfail.png
313 After you select the error, <b>Show Sub-shape</b> button allows
314 visualizing in magenta the geometrical entity that causes the error.
316 \image html failed_computation.png
317 <em>3D algorithm failed to compute mesh on a box shown using <b>Show
318 Sub-shape</b> button</em>
320 <b>Publish Sub-shape</b> button publishes the sub-shape, whose meshing
321 has failed, in GEOM component as a child of the mesh geometry, which
322 allows analyzing the problem geometry and creating a submesh on it in
323 order to locally tune the hypotheses.
325 If the failure is caused by an invalid input mesh and the algorithm has
326 found which mesh entities are bad, <b>Show bad Mesh</b>
327 button appears in the dialog. Clicked, it shows the bad mesh entities in
328 the Viewer in magenta. Sometimes the shown mesh entities are too small
329 or/and hidden by other mesh elements. They can be seen after
330 switching the mesh to Wireframe visualization mode or switching off
331 the visualization of faces and volumes (if any).
333 <b>Bad Mesh to Group</b> button creates groups of bad mesh entities
334 to facilitate their analysis.
336 \image html show_bad_mesh.png
337 <em>Edges bounding a hole in the surface are shown in magenta using <b>Show
338 bad Mesh</b> button</em>
340 \note Mesh Computation Information box does not appear if you set
341 "Mesh computation/Show a computation result notification" preference
342 to the "Never" value. This option gives the possibility to control mesh
343 computation reporting. There are the following possibilities: always
344 show the information box, show only if an error occurs or never.
345 By default, the information box is always shown after mesh computation operation.
349 \anchor use_existing_anchor
350 <h2>"Use Edges to be Created Manually" and "Use Faces to be Created Manually" algorithms</h2>
352 It is possible to create a 1D or a 2D mesh in a python script
353 (using <em>AddNode, AddEdge</em> and <em>AddFace</em> commands) and
354 then use such sub-meshes in the construction of a 2D or a 3D mesh. For
355 this, there exist two algorithms: <b>Use Edges to be Created
356 Manually</b> and <b>Use Faces to be Created Manually</b>.
357 Imagine, you want to use standard algorithms to generate 1D and 3D
358 meshes and to create 2D mesh by your python code. Then you
360 <li> create a mesh object, assign a 1D algorithm,</li>
361 <li> invoke \b Compute command, which computes a 1D mesh,</li>
362 <li> assign <b>Use Faces to be Created Manually</b> and a 3D algorithm,</li>
363 <li> run your python code, which creates a 2D mesh,</li>
364 <li> invoke \b Compute command, which computes a 3D mesh.</li>
366 \warning <b>Use Edges to be Created Manually</b> and <b>Use Faces to
367 be Created Manually</b> algorithms should be assigned _before_
368 mesh generation by the Python code.
370 Consider trying a sample script demonstrating the usage of
371 \ref tui_use_existing_faces "Use Faces to be Created Manually"
372 algorithm for construction of a 2D mesh using Python commands.
374 \image html use_existing_face_sample_mesh.png
375 <em> Mesh computed by \ref tui_use_existing_faces "the sample script"
376 shown in a Shrink mode.</em>