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 at computation of
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. For example, \b 3D page lists the algorithms
43 that affect 3D geometrical objects (solids).
46 - Some page(s) can be disabled if the source geometrical
47 object does not include shapes (sub-shapes) of the corresponding
48 dimension(s). For example, if the input object is a geometrical face,
49 \b 3D page is disabled.
50 - Some algorithms affect the geometry of several dimensions,
51 i.e. "1D-2D" or "1D-2D-3D". If such an algorithm is selected by the
52 user, the dialog box pages related to the corresponding lower level
53 dimensions are disabled.
54 - \b 0D page does not refer to the 0D elements, but to 0D
55 geometry (vertices). Mesh module does not provide algorithms that
56 produce 0D elements. Currently \b 0D page provides only one
57 algorithm "Segments around vertex" that allows specyfying the required
58 size of mesh edges about the selected vertex (or vertices).
60 For example, you need to mesh a 3D object.
62 First, type the name of your mesh in the \b Name box, by default,
63 it is "Mesh_1". Then select the geometrical object you wish to
64 mesh in the Object Browser and click "Select" button near \b Geometry
65 field (if the name of the object has not yet appeared in \b Geometry field).
68 \image html image120.png
69 <em>"Select" button</em>
72 Now you can define 3D Algorithm and 3D Hypotheses, which will be
73 applied to the solids of your geometrical object. Click the <em>"Add
74 Hypothesis"</em> button to add a hypothesis.
77 \image html image121.png
78 <em>"Add Hypothesis" button</em>
81 Click the <em>"Edit Hypothesis"</em> button to change the values for the
85 \image html image122.png
86 <em>"Edit Hypothesis" button</em>
89 Most standard 2D and 3D algorithms can work without hypotheses
90 using some default parameters. The use of additional hypotheses
91 is optional (i.e. you may leave "None" in this box).
93 Proceed in the same way with 2D and 1D Algorithms and Hypotheses that
94 will be used to mesh faces and edges of your geometry. (Note
95 that any object has edges, even if their existence is not
96 apparent, for example, a sphere has 4 edges). Note that the
97 choice of hypotheses and lower dimension algorithms depends on
98 the higher dimension algorithm.
100 Some algorithms generate mesh of several dimensions, while others
101 produce mesh of only one dimension. In the latter case there must
102 be one Algorithm and zero or several
103 Hypotheses for each dimension of your object, otherwise you will
104 not get any mesh at all. Of course, if you wish to mesh a face,
105 which is a 2D object, you do not need to define a 3D Algorithm and
108 In the <b>Object Browser</b> the structure of the new mesh will be
109 displayed as follows:
112 \image html image88.jpg
117 <li>a reference to the geometrical object on the basis of
118 which the mesh has been constructed;</li>
119 <li><b>Applied hypotheses</b> folder containing the references
120 to the hypotheses applied at the construction of the mesh;</li>
121 <li><b>Applied algorithms</b> folder containing the references
122 to the algorithms applied at the construction of the mesh.</li>
125 There is an alternative way to assign Algorithms and Hypotheses by
126 clicking <b>Assign a set of hypotheses</b> button and selecting among
127 pre-defined sets of hypotheses. In addition to the standard
128 sets of hypotheses, it is possible to create custom sets by editing
129 CustomMeshers.xml file located in the home directory. CustomMeshers.xml
130 file must describe sets of hypotheses in the
131 same way as ${SMESH_ROOT_DIR}/share/salome/resources/smesh/StdMeshers.xml
132 file does (sets of hypotheses are enclosed between <hypotheses-set-group>
135 \image html hypo_sets.png
136 List of sets of hypotheses. Tag <em>[custom]</em> is
137 automatically added to the sets defined by the user
141 Consider trying a sample script for construction of a mesh from our
142 \ref tui_creating_meshes_page "TUI Scripts" section.
144 \anchor evaluate_anchor
145 <h2>Evaluating mesh size</h2>
147 After the mesh object is created and all hypotheses are assigned and
148 before \ref compute_anchor "Compute" operation, it is possible to
149 calculate the eventual mesh size. For this, select the mesh in
150 the <b>Object Browser</b> and from the \b Mesh menu select \b
151 Evaluate. The result of evaluation will be displayed in the following
154 \image html mesh_evaluation_succeed.png
156 \anchor preview_anchor
157 <h2>Previewing the mesh</h2>
159 Before \ref compute_anchor "the mesh computation", it is also possible
160 to see the mesh preview.
162 For this, select the mesh in the Object Browser. From the \b Mesh menu
163 select \b Preview or click "Preview" button in the toolbar or activate
164 "Preview" item from the pop-up menu.
167 \image html mesh_precompute.png
168 <em>"Preview" button</em>
171 Select <b>1D mesh</b> or <b>2D mesh</b> preview mode in the Preview dialog.
173 \image html preview_mesh_1D.png "1D mesh preview shows nodes computed on geometry edges"
175 \image html preview_mesh_2D.png "2D mesh preview shows edge mesh elements, computed on geometry faces"
177 <b>Compute</b> button computes the whole mesh.
179 When the Preview dialog is closed, the question about the storage of temporarily
180 created mesh elements appears:
182 \image html preview_tmp_data.png
184 These elements can be kept in the mesh.
187 \anchor submesh_order_anchor
188 <h2>Changing sub-mesh priority</h2>
190 If the mesh contains concurrent \ref constructing_submeshes_page "sub-meshes",
191 it is possible to change the priority of their computation, i.e. to
192 change the priority of applying algorithms to the shared sub-shapes of
195 <em>To change submesh priority:</em>
197 Choose "Change submesh priority" from the Mesh menu or a pop-up
198 menu. The opened dialog shows a list of submeshes in the order of
201 There is an example of submesh order modifications taking a Mesh created on a Box
202 shape. The main Mesh object:
204 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=20</li>
205 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis<b>Max Element Area</b>
208 The first submesh object <b>Submesh_1</b> created on <b>Face_1</b> is:
210 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=4</li>
211 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
213 The second submesh object <b>Submesh_2</b> created on <b>Face_2</b> is:
215 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=8</li>
216 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
219 And the last submesh object <b>Submesh_3</b> created on <b>Face_3</b> is:
221 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=12</li>
222 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
225 The sub-meshes become concurrent if they share sub-shapes that can be
226 meshed with different algorithms (or different hypotheses). In the
227 example, we have three submeshes with concurrent algorithms, because
228 they have different hypotheses.
230 The first mesh computation is made with:
232 \image html mesh_order_123.png
233 <em>"Mesh order SubMesh_1, SubMesh_2, SubMesh_3"</em></center>
235 \image html mesh_order_123_res.png
236 <em>"Result mesh with order SubMesh_1, SubMesh_2, SubMesh_3 "</em></center>
238 The next mesh computation is made with:
240 \image html mesh_order_213.png
241 <em>"Mesh order SubMesh_2, SubMesh_1, SubMesh_3"</em></center>
243 \image html mesh_order_213_res.png
244 <em>"Result mesh with order SubMesh_2, SubMesh_1, SubMesh_3 "</em></center>
246 And the last mesh computation is made with:
248 \image html mesh_order_321.png
249 <em>"Mesh order SubMesh_3, SubMesh_2, SubMesh_1"</em></center>
250 <center>\image html mesh_order_321_res.png
251 <em>"Result mesh with order SubMesh_3, SubMesh_2, SubMesh_1 "</em></center>
253 As we can see, each mesh computation has a different number of result
254 elements and a different mesh discretization on the shared edges (the edges
255 that are shared between <b>Face_1</b>, <b>Face_2</b> and <b>Face_3</b>)
257 Additionally, submesh priority (the order of applied algorithms) can
258 be modified not only in a separate dialog box, but also in
259 the <b>Preview</b>. This helps to preview different mesh results,
260 modifying the order of submeshes.
262 \image html mesh_order_preview.png
263 <em>"Preview with submesh priority list box"</em></center>
265 If there are no concurrent submeshes under the Mesh object, the user
266 will see the following information.
268 \image html mesh_order_no_concurrent.png
269 <em>"No concurrent submeshes detected"</em></center>
272 \anchor compute_anchor
273 <h2>Computing the mesh</h2>
275 It is equally possible to skip \ref evaluate_anchor "the Evaluation"
276 and \ref preview_anchor "the Preview" and to \b Compute the mesh after
277 the hypotheses are assigned. For this, select your mesh in
278 the <b>Object Browser</b>. From the \b Mesh menu select \b Compute or
279 click "Compute" button of the toolbar.
282 \image html image28.png
283 <em>"Compute" button</em>
286 After the mesh computation finishes, the Mesh Computation information
287 box appears. In case of a success, the box shows
288 information on number of entities of different types in the mesh.
290 \image html meshcomputationsucceed.png
292 If the mesh computation failed, the information about the cause of the
293 failure is provided in \b Errors table.
295 \image html meshcomputationfail.png
297 After you select the error, <b>Show Sub-shape</b> button allows
298 visualizing in magenta the geometrical entity that causes the error.
300 \image html failed_computation.png
301 <em>3D algorithm failed to compute mesh on a box shown using <b>Show
302 Sub-shape</b> button</em>
304 <b>Publish Sub-shape</b> button publishes the sub-shape, whose meshing
305 has failed, in GEOM component as a child of the mesh geometry, which
306 allows analyzing the problem geometry and creating a submesh on it in
307 order to locally tune the hypotheses.
309 If the failure is caused by an invalid input mesh and the algorithm has
310 found which mesh entities are bad, <b>Show bad Mesh</b>
311 button appears in the dialog. Clicked, it shows the bad mesh entities in
312 the Viewer in magenta. Sometimes the shown mesh entities are too small
313 or/and hidden by other mesh elements. They can be seen after
314 switching the mesh to Wireframe visualization mode or switching off
315 the visualization of faces and volumes (if any).
317 <b>Bad Mesh to Group</b> button creates groups of the bad mesh entities,
318 thus allowing you for more comfortable analysis of these entities.
320 \image html show_bad_mesh.png
321 <em>Edges bounding a hole in the surface are shown in magenta using <b>Show
322 bad Mesh</b> button</em>
324 \note Mesh Computation Information box does not appear if you set
325 "Mesh computation/Show a computation result notification" preference
326 to the "Never" value. This option gives the possibility to control mesh
327 computation reporting. There are the following possibilities: always
328 show the information box, show only if an error occurs or never.
329 By default, the information box is always shown after mesh computation operation.
333 \anchor use_existing_anchor
334 <h2>"Use existing edges" and "Use existing faces" algorithms</h2>
336 It is possible to create a 1D or a 2D mesh in a python script
337 (using <em>AddNode, AddEdge</em> and <em>AddFace</em> commands) and
338 then use such sub-meshes in the construction of a 2D or a 3D mesh. For
339 this, there exist two algorithms: <b>Use existing edges</b> and <b>Use
341 For example, you want to use standard algorithms to generate 1D and 3D
342 meshes and to create 2D mesh by your python code. Then you
344 <li> create a mesh object, assign an 1D algorithm,</li>
345 <li> invoke \b Compute command, which computes an 1D mesh,</li>
346 <li> assign <b>Use existing faces</b> and a 3D algorithm,</li>
347 <li> run your python code, which creates a 2D mesh,</li>
348 <li> invoke \b Compute command, which computes a 3D mesh.</li>
351 Consider trying a sample script demonstrating the usage of
352 \ref tui_use_existing_faces "Use existing faces" algorithm for
353 construction of a 2D mesh using Python commands.
355 \image html use_existing_face_sample_mesh.png
356 <em> Mesh computed by \ref tui_use_existing_faces "the sample script"
357 shown in a Shrink mode.</em>