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>
14 \anchor create_mesh_anchor
15 <h2>Creation of a mesh object</h2>
16 <em>To construct a mesh:</em>
18 <li>Select a geometrical object for meshing.</li>
19 <li>In the \b Mesh menu select <b>Create Mesh</b> or click <em>"Create
20 Mesh"</em> button in the toolbar.
23 \image html image32.png
24 <em>"Create Mesh" button</em>
27 The following dialog box will appear:
29 \image html createmesh-inv.png
32 <li>Select <b>Mesh Type</b> in the corresponding list from <b>Any, Hexahedral, Tetrahedral, Triangular </b> and \b Quadrilateral (there can be less items for lower dimensions).
34 Selection of a mesh type hides any algorithms that are not able to create elements of this type.</li>
36 <li>Apply \subpage basic_meshing_algos_page "meshing algorithms" and
37 \subpage about_hypo_page "hypotheses" which will be used to compute
40 "Create mesh" dialog box contains several tab pages titled \b 3D,
41 \b 2D, \b 1D and \b 0D. The title of each page reflects the
42 dimension of the CAD model (geometry) the algorithms listed on
43 this page affect and the maximal dimension of elements the algorithms
44 generate. For example, \b 3D page lists the algorithms that affect
45 3D geometrical objects (solids).
48 - Some page(s) can be disabled if the source geometrical
49 object does not include shapes (sub-shapes) of the corresponding
50 dimension(s). For example, if the input object is a geometrical face,
51 \b 3D page is disabled.
52 - Some algorithms affect the geometry of several dimensions,
53 i.e. "1D-2D" or "1D-2D-3D". If such an algorithm is selected by the
54 user, the dialog box pages related to the corresponding lower level
55 dimensions are disabled.
56 - \b 0D page does not refer to the 0D elements, but to 0D
57 geometry (vertices). Mesh module does not provide algorithms that
58 produce 0D elements. Currently \b 0D page provides only one
59 algorithm "Segments around vertex" that allows specyfying the required
60 size of mesh edges about the selected vertex (or vertices).
62 For example, you need to mesh a 3D object.
64 First, type the name of your mesh in the \b Name box, by default,
65 it is "Mesh_1". Then select the geometrical object you wish to
66 mesh in the Object Browser and click "Select" button near \b Geometry
67 field (if the name of the object has not yet appeared in \b Geometry field).
70 \image html image120.png
71 <em>"Select" button</em>
74 Now you can define 3D Algorithm and 3D Hypotheses, which will be
75 applied to the solids of your geometrical object. Click the <em>"Add
76 Hypothesis"</em> button to add a hypothesis.
79 \image html image121.png
80 <em>"Add Hypothesis" button</em>
83 Click the <em>"Edit Hypothesis"</em> button to change the values for the
87 \image html image122.png
88 <em>"Edit Hypothesis" button</em>
91 Most 2D and 3D algorithms can work without hypotheses using default meshing parameters. Some algorithms do not require any hypotheses. After selection of an algorithm "Hypothesis" field of
92 the dialog can contain:
94 <li> <em>\<Default\></em> if the algorithm can work using default
96 <li> <em>\<None\></em> if the algorithm requires a hypothesis defining
98 <li> If the algorithm does not use hypotheses, this field is grayed.</li>
100 After selection of an algorithm <b>Add. Hypothesis</b> field can contain:
102 <li> <em>\<None\></em> if the algorithm can be tuned
103 using an additional hypothesis.</li>
104 <li> If the algorithm does not use additional hypotheses, this field is grayed.</li>
107 Proceed in the same way with 2D and 1D Algorithms and Hypotheses that
108 will be used to mesh faces and edges of your geometry. (Note
109 that any object has edges, even if their existence is not
110 apparent, for example, a sphere has 4 edges). Note that the
111 choice of hypotheses and lower dimension algorithms depends on
112 the higher dimension algorithm.
114 Some algorithms generate mesh of several dimensions, while others
115 produce mesh of only one dimension. In the latter case there must
116 be one Algorithm and zero or several
117 Hypotheses for each dimension of your object, otherwise you will
118 not get any mesh at all. Of course, if you wish to mesh a face,
119 which is a 2D object, you do not need to define a 3D Algorithm and
122 In the <b>Object Browser</b> the structure of the new mesh will be
123 displayed as follows:
126 \image html image88.jpg
131 <li>a reference to the geometrical object on the basis of
132 which the mesh has been constructed;</li>
133 <li><b>Applied hypotheses</b> folder containing the references
134 to the hypotheses applied at the construction of the mesh;</li>
135 <li><b>Applied algorithms</b> folder containing the references
136 to the algorithms applied at the construction of the mesh.</li>
139 There is an alternative way to assign Algorithms and Hypotheses by
140 clicking <b>Assign a set of hypotheses</b> button and selecting among
141 pre-defined sets of hypotheses. In addition to the standard
142 sets of hypotheses, it is possible to create custom sets by editing
143 CustomMeshers.xml file located in the home directory. CustomMeshers.xml
144 file must describe sets of hypotheses in the
145 same way as ${SMESH_ROOT_DIR}/share/salome/resources/smesh/StdMeshers.xml
146 file does (sets of hypotheses are enclosed between <hypotheses-set-group>
149 \image html hypo_sets.png
150 List of sets of hypotheses. Tag <em>[custom]</em> is
151 automatically added to the sets defined by the user
155 Consider trying a sample script for construction of a mesh from our
156 \ref tui_creating_meshes_page "TUI Scripts" section.
158 \anchor evaluate_anchor
159 <h2>Evaluating mesh size</h2>
161 After the mesh object is created and all hypotheses are assigned and
162 before \ref compute_anchor "Compute" operation, it is possible to
163 calculate the eventual mesh size. For this, select the mesh in
164 the <b>Object Browser</b> and from the \b Mesh menu select \b
165 Evaluate. The result of evaluation will be displayed in the following
168 \image html mesh_evaluation_succeed.png
170 \anchor preview_anchor
171 <h2>Previewing the mesh</h2>
173 Before \ref compute_anchor "the mesh computation", it is also possible
174 to see the mesh preview.
176 For this, select the mesh in the Object Browser. From the \b Mesh menu
177 select \b Preview or click "Preview" button in the toolbar or activate
178 "Preview" item from the pop-up menu.
181 \image html mesh_precompute.png
182 <em>"Preview" button</em>
185 Select <b>1D mesh</b> or <b>2D mesh</b> preview mode in the Preview dialog.
187 \image html preview_mesh_1D.png "1D mesh preview shows nodes computed on geometry edges"
189 \image html preview_mesh_2D.png "2D mesh preview shows edge mesh elements, computed on geometry faces"
191 <b>Compute</b> button computes the whole mesh.
193 When the Preview dialog is closed, the question about the storage of temporarily
194 created mesh elements appears:
196 \image html preview_tmp_data.png
198 These elements can be kept in the mesh.
201 \anchor submesh_order_anchor
202 <h2>Changing sub-mesh priority</h2>
204 If the mesh contains concurrent \ref constructing_submeshes_page "sub-meshes",
205 it is possible to change the priority of their computation, i.e. to
206 change the priority of applying algorithms to the shared sub-shapes of
209 <em>To change submesh priority:</em>
211 Choose "Change submesh priority" from the Mesh menu or a pop-up
212 menu. The opened dialog shows a list of submeshes in the order of
215 There is an example of submesh order modifications taking a Mesh created on a Box
216 shape. The main Mesh object:
218 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=20</li>
219 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis<b>Max Element Area</b>
222 The first submesh object <b>Submesh_1</b> created on <b>Face_1</b> is:
224 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=4</li>
225 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
227 The second submesh object <b>Submesh_2</b> created on <b>Face_2</b> is:
229 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=8</li>
230 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
233 And the last submesh object <b>Submesh_3</b> created on <b>Face_3</b> is:
235 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=12</li>
236 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
239 The sub-meshes become concurrent if they share sub-shapes that can be
240 meshed with different algorithms (or different hypotheses). In the
241 example, we have three submeshes with concurrent algorithms, because
242 they have different hypotheses.
244 The first mesh computation is made with:
246 \image html mesh_order_123.png
247 <em>"Mesh order SubMesh_1, SubMesh_2, SubMesh_3"</em></center>
249 \image html mesh_order_123_res.png
250 <em>"Result mesh with order SubMesh_1, SubMesh_2, SubMesh_3 "</em></center>
252 The next mesh computation is made with:
254 \image html mesh_order_213.png
255 <em>"Mesh order SubMesh_2, SubMesh_1, SubMesh_3"</em></center>
257 \image html mesh_order_213_res.png
258 <em>"Result mesh with order SubMesh_2, SubMesh_1, SubMesh_3 "</em></center>
260 And the last mesh computation is made with:
262 \image html mesh_order_321.png
263 <em>"Mesh order SubMesh_3, SubMesh_2, SubMesh_1"</em></center>
264 <center>\image html mesh_order_321_res.png
265 <em>"Result mesh with order SubMesh_3, SubMesh_2, SubMesh_1 "</em></center>
267 As we can see, each mesh computation has a different number of result
268 elements and a different mesh discretization on the shared edges (the edges
269 that are shared between <b>Face_1</b>, <b>Face_2</b> and <b>Face_3</b>)
271 Additionally, submesh priority (the order of applied algorithms) can
272 be modified not only in a separate dialog box, but also in
273 the <b>Preview</b>. This helps to preview different mesh results,
274 modifying the order of submeshes.
276 \image html mesh_order_preview.png
277 <em>"Preview with submesh priority list box"</em></center>
279 If there are no concurrent submeshes under the Mesh object, the user
280 will see the following information.
282 \image html mesh_order_no_concurrent.png
283 <em>"No concurrent submeshes detected"</em></center>
286 \anchor compute_anchor
287 <h2>Computing the mesh</h2>
289 It is equally possible to skip \ref evaluate_anchor "the Evaluation"
290 and \ref preview_anchor "the Preview" and to \b Compute the mesh after
291 the hypotheses are assigned. For this, select your mesh in
292 the <b>Object Browser</b>. From the \b Mesh menu select \b Compute or
293 click "Compute" button of the toolbar.
296 \image html image28.png
297 <em>"Compute" button</em>
300 After the mesh computation finishes, the Mesh Computation information
301 box appears. In case of a success, the box shows
302 information on number of entities of different types in the mesh.
304 \image html meshcomputationsucceed.png
306 If the mesh computation failed, the information about the cause of the
307 failure is provided in \b Errors table.
309 \image html meshcomputationfail.png
311 After you select the error, <b>Show Sub-shape</b> button allows
312 visualizing in magenta the geometrical entity that causes the error.
314 \image html failed_computation.png
315 <em>3D algorithm failed to compute mesh on a box shown using <b>Show
316 Sub-shape</b> button</em>
318 <b>Publish Sub-shape</b> button publishes the sub-shape, whose meshing
319 has failed, in GEOM component as a child of the mesh geometry, which
320 allows analyzing the problem geometry and creating a submesh on it in
321 order to locally tune the hypotheses.
323 If the failure is caused by an invalid input mesh and the algorithm has
324 found which mesh entities are bad, <b>Show bad Mesh</b>
325 button appears in the dialog. Clicked, it shows the bad mesh entities in
326 the Viewer in magenta. Sometimes the shown mesh entities are too small
327 or/and hidden by other mesh elements. They can be seen after
328 switching the mesh to Wireframe visualization mode or switching off
329 the visualization of faces and volumes (if any).
331 <b>Bad Mesh to Group</b> button creates groups of bad mesh entities
332 to facilitate their analysis.
334 \image html show_bad_mesh.png
335 <em>Edges bounding a hole in the surface are shown in magenta using <b>Show
336 bad Mesh</b> button</em>
338 \note Mesh Computation Information box does not appear if you set
339 "Mesh computation/Show a computation result notification" preference
340 to the "Never" value. This option gives the possibility to control mesh
341 computation reporting. There are the following possibilities: always
342 show the information box, show only if an error occurs or never.
343 By default, the information box is always shown after mesh computation operation.