3 \page blsurf_hypo_page BLSURF Parameters hypothesis
5 \n BLSURF Parameters hypothesis works only with <b>BLSURF</b> 2d
6 algorithm. This algorithm is a commercial software.
7 \n To get a licence, visit http://www.distene.com/corp/eval-distene.html
9 <h1>General parameters</h1>
11 \image html blsurf_parameters.png
14 <li><b>Name</b> - allows defining the name of the hypothesis (BLSURF
15 Parameters_n by default).</li>
17 <li><b>Physical Mesh</b> - can be set to None, Custom or Size Map
19 <li>if set to "Custom", allows user input in the
20 in <b>User size</b>, <b>Max Physical Size</b> and <b>Min Physical
22 <li>if set to "Size Map", behaves like "Custom" mode and takes into account the custom elements sizes given in the Size Map tab.</li>
26 <li><b>User size</b> - defines the size of the generated mesh elements. </li>
28 <li><b>Max Physical Size</b> - defines the upper limit of mesh element size. </li>
30 <li><b>Min Physical Size</b> - defines the lower limit of mesh element size. </li>
32 <li><b>Geometrical mesh</b> - if set to "Custom", allows user input in
33 <b>Angle Mesh S</b>, <b>Angle Mesh C</b> and
34 <b>Gradation</b> fields. These fields control
35 computation of the element size, so called <i>geometrical size</i>, conform to
36 the surface geometry considering local curvatures. \n
37 If both the <b>User size</b> and the <i>geometrical size</i> are defined, the
38 eventual element size correspond to the least of the two. </li>
40 <li><b>Angle Mesh S</b> - maximum angle between the mesh face and the
41 tangent to the geometrical surface at each mesh node, in degrees. </li>
43 <li><b>Angle Mesh C</b> - maximum angle between the mesh edge and the
44 tangent to the geometrical curve at each mesh node, in degrees. </li>
46 <li><b>Max Geometrical Size</b> - defines the upper limit of the <i>geometrical size</i>.</li>
48 <li><b>Min Geometrical Size</b> - defines the lower limit of the <i>geometrical size</i>.</li>
50 <li><b>Gradation</b> - maximum ratio between the lengths of
51 two adjacent edges. </li>
53 <li><b>Allow Quadrangles</b> - if checked, allows the creation of quadrilateral elements.</li>
55 <li><b>Patch independent</b> - if checked, geometrical
56 edges are not respected and all geometrical faces are meshed as one
59 <h1>Advanced parameters</h1>
61 The notion of <i>diag</i> used in the descriptions means the diagonal of the bounding box of the
62 geometrical object to mesh.
64 \image html blsurf_parameters_advanced.png
66 <li><b>Verbosity level</b> - Defines the percentage of "verbosity" of
69 <li><b>Topology</b> - allows creation of a conform mesh on a shell of
72 <li>"From CAD" means that mesh conformity is assured by conformity
74 <li>"Pre-process" and "Pre-process++" allow the BLSURF software to
75 pre-process the geometrical model to eventually produce a conform
77 <li>"PreCAD" is an auxiliary CAD pre-processing module which has
80 <li> Complete missing or inadequate CAD-description.</li>
81 <li>Perform topology reconstruction and specific geometry
82 enhancement for mesh generation.</li>
84 This module requires a specific licence.
86 The following PreCAD options are the most significant and important ones:
88 <li><b>Merge Edges</b> - allows PreCAD to optimize the geometry by merging some
89 edges. Default is 0.</li>
90 <li><b>Remove nano edges</b> - allows PreCAD to optimize the geometry by removing
91 the nano edges whenever possible. Default is 0.</li>
92 <li><b>Nano edge length</b> - gives the length below which an edge is considered as nano
93 for the topology processing. See also the \b remove_nano_edges option. If unset, PreCAD
94 default value is \f$\mathrm{diag} \times 10^{-5}\f$.</li>
95 <li><b>Discard input topology</b> - computes the CAD topology from scratch,
96 without considering the toplogical information contained in the original CAD
97 (Useful for iges files). Default is 0.</li>
102 <li><b>ExportGMF</b> - saves the computed mesh into a GMF file (.mesh or .meshb).</li>
104 <li><b>Add option</b> - provides the choice of multiple PreCAD and BLSURF
105 advanced options, which appear, if selected, in a table where it is
106 possible to input the value of the option and to edit it later.</li>
108 <li><b>Clear option</b> - removes the option selected in the table.</li>
113 The following BLSURF options are commonly usable.
116 <li>\b topo_eps1 (real) - is the tolerance level inside a CAD
117 patch. By default is equal to \f$\mathrm{diag} \times 10^{-4}\f$. This tolerance is used to
118 identify nodes to merge within one geometrical face when \b Topology
119 option is to pre-process.</li>
121 <li>\b topo_eps2 (real) - is the tolerance level between two CAD
122 patches. By default is equal to \f$\mathrm{diag} \times 10^{-4}\f$. This tolerance is used to
123 identify nodes to merge over different geometrical faces when
124 \b Topology option is to pre-process.</li>
126 <li>\b LSS (real) - is an abbreviation for "length of sub-segment". It is
127 a maximal allowed length of a mesh edge. Default is \f$0.5\f$.</li>
129 <li>\b frontal (integer)
131 <li> 1 - the mesh generator inserts points with an advancing front method.</li>
132 <li> 0 - it inserts them with an algebraic method (on internal edges). This method is
133 slightly faster but generates less regular meshes. </li>
137 \anchor blsurf_hinterpol_flag
138 <li>\b hinterpol_flag (integer) - determines the computation of an
139 interpolated value <i>v</i> between two points <i>P1</i> and <i>P2</i> on a
140 curve. Let <i>h1</i> be the value at point <i>P1,</i> <i>h2</i> be the value at point
141 <i>P2,</i> and <i>t</i> be a parameter varying from 0 to 1 when moving from <i>P1
144 <li>0 - the interpolation is linear: \f$v = h1 + t (h2 - h1 )\f$</li>
145 <li>1 - the interpolation is geometric: \f$v = h1 \times \left( \frac{h1}{h2} \right)^{t}\f$</li>
146 <li>2 - the interpolation is sinusoidal: \f$v = \frac{h1+h2}{2} + \frac{h1-h2}{2 \cdot \cos(\pi \cdot t)}\f$</li>
150 \anchor blsurf_hmean_flag
151 <li>\b hmean_flag (integer) - determines the computation of the average of several
153 <li>-1 - the minimum is computed.</li>
154 <li>0 or 2 - the arithmetic average is computed.
155 <li>1 - the geometric average is computed.</li>
159 <li>\b CheckAdjacentEdges, \b CheckCloseEdges and \b CheckWellDefined
160 (integers) - gives the number of calls of equally named subroutines the
161 purpose of which is to improve the mesh of domains having narrow
162 parts. At each iteration,\b CheckCloseEdges decreases the sizes of the
163 edges when two boundary curves are neighboring,\b CheckAdjacentEdges
164 balances the sizes of adjacent edges, and \b CheckWellDefined checks if
165 the parametric domain is well defined. Default values are 0.</li>
168 <li>\b CoefRectangle (real)- defines the relative thickness of the rectangles
169 used by subroutine \b CheckCloseEdges (see above). Default is 0.25.</li>
171 <li>\b eps_collapse (real) - if more than 0.0, BLSURF removes
172 curves whose lengths are less than \b eps_collapse. To obtain an
173 approximate value of the length of a curve, it is arbitrarily
174 split into 20 edges. Default is 0.0.</li>
176 <li>\b eps_ends (real) - is used to detect the curves whose lengths are very
177 small, which sometimes constitutes an error. A message is printed
178 if \f$\left|P2-P1\right| < eps\_ends\f$, where <i>P1</i> and <i>P2</i> are the
179 extremities of a curve. Default is \f$\frac{\mathrm{diag}}{500.0}\f$.</li>
181 <li>\b prefix (char) - is a prefix of the files generated by
182 BLSURF. Default is "x".</li>
184 <li>\b refs (integer) - reference of a surface, used when exporting
185 files. Default is 1.</li>
189 The following PreCAD options are commonly usable.
191 <li>\b closed_geometry (int) - describes whether the working geometry
192 should be closed or not. When activated, this option helps PreCAD to treat
193 the most dirtiest geometries. Default is 0.</li>
194 <li>\b debug (int) - If debug = 1 PreCAD will be very verbose and will output
195 some intermediate files in the working directory. Default is 0.</li>
196 <li>\b eps_nano_relative (real) - Same as \b eps_nano but given in relatively to
197 the diagonal of the box bounding the geometry. Default is \f$10^{-5}\f$.</li>
198 <li>\b eps_sewing (real) - tolerance of the assembly. It rarely requires to be tuned.
199 Default is \f$\mathrm{diag} \times 5 \cdot 10^{-4}\f$.</li>
200 <li>\b eps_sewing_relative (real) - Same as \b eps_nano but given in relatively to
201 the diagonal of the box bounding the geometry. Default is \f$5 \cdot 10^{-4}\f$.</li>
202 <li>\b manifold_geometry (int) - describes whether the working geometry should be manifold or not.
203 When activated, this option helps PreCAD to treat the most dirtiest geometries. Default is 0.</li>
204 <li>\b create_tag_collision (int) - creates some new tags from original ones in case
205 of collision (entity merge or association for example). Default is 0.</li>
206 <li>\b periodic_tolerance (real) - defines the maximum distance error accepted between
207 two sets of periodic entities. Default is \f$\mathrm{diag} \times 10^{-5}\f$.</li>
208 <li>\b periodic_tolerance_relative (real) - Same as \b periodic_tolerance but in relative
209 unit. Default is \f$10^{-5}\f$.</li>
210 <li>\b periodic_split_tolerance (real) - This periodicity processing related option defines
211 the minimum distance between a CAD point and an imprinted point. It allows to indirectly
212 control the number of points and small edges created. Default is \f$\mathrm{diag} \times 10^{-4}\f$.</li>
213 <li>\b periodic_split_tolerance_relative (real - Same as \b periodic_split_tolerance but in
214 relative unit. Default is \f$10^{-4}\f$.</li>
218 The following advanced options are not documented and you can use them
220 \n\n Integer variables:
222 <li> addsurf_ivertex</li>
223 <li> background </li>
225 <li> communication </li>
227 <li> export_flag </li>
231 <li> intermedfile </li>
235 <li> pardom_flag </li>
238 <li> surforient </li>
240 <li> topo_collapse </li>
244 <li> addsurf_angle </li>
247 <li> addsurf_FG </li>
249 <li> addsurf_PA </li>
250 <li> angle_compcurv </li>
251 <li> angle_ridge </li>
252 <li> eps_pardom </li>
256 <li> export_format </li>
257 <li> export_option </li>
258 <li> import_option </li>
261 <h1>Custom size map</h1>
263 \image html blsurf_parameters_sizemap1.png
265 User sizes can be defined on faces, edges or vertices.
267 <li>The faces, edges and vertices can belong to the meshed geometrical
268 object or to its sub-shapes (created using <b>Explode</b> command).</li>
269 <li>Groups of faces, edges and vertices are also handled.</li>
270 <li>It is possible to attribute the same size to several geometries using multi-selection.</li>
271 <li>The sizes are constant values or python functions.</li>
272 <li>In case of a python function, the following rules must be respected:
274 <li>The name of the function is f.</li>
275 <li>If geometry is a face or a group of faces, the function is f(u,v).</li>
276 <li>If geometry is an edge or a group of edges, the function is f(t).</li>
277 <li>If geometry is a vertex or a group of vertices, the function is f().</li>
278 <li>The function must return a double.</li>
282 \anchor blsurf_sizemap_computation
283 <h2>Computation of the physical size</h2>
285 The physical size is obtained by querying sizemap functions associated to the input CAD object for surfaces, curves and points.
286 Each function can either return a value h (which is then trimmed
287 between the two bounds hphymin and hphymax), or "no answer" (by not
288 assigning a value to h), thus providing great flexibility in the
289 specification of the sizes. The computation depends on whether point P is internal to a surface, internal to a curve, or at the end of several curves:
291 <li> If point P is internal to a surface, the CAD surface size function is queried. If no answer is returned, one interpolates with the values at the vertices of the discretized interface curves.</li>
292 <li> If point P is internal to a curve, the CAD curve size function is queried first. If no answer is returned, the surface size function is queried for every adjacent surface and the mean value of the returned values is computed. If no answer is returned, sizes h1 and h2 at both ends of the curve are considered (see next item) and the interpolated value is computed.</li>
293 <li> If point P is at the extremity of several curves, the CAD point size function is queried first. If no answer is returned, the curve size function is queried for every adjacent curve and the mean value of the returned values is computed. If no answer is returned, the surface size function is queried for every adjacent surface and the mean value of the returned values is computed. If there is still no answer returned, the default value hphydef is kept.</li>
295 In order to compute the mean of several values, the arithmetic mean is used by default, but this can be modified by the parameter \ref blsurf_hmean_flag "hmean flag". In the same way, in order to interpolate two values, a linear interpolation is used by default, but this can be modified by \ref blsurf_hinterpol_flag "hinterpol flag".
297 \anchor blsurf_attractor
298 <h2>Advanced maps</h2>
300 \image html blsurf_parameters_sizemap2.png
302 More specific size maps can be defined on faces.
305 <li> <i> Attractors </i> allow to define the size of the mesh elements
306 on a face so that the mesh is the finest on the attractor shape and
307 becomes coarser when getting far from this shape.
309 <li> The selected attractor can be a Vertex, an Edge, a Wire or a
310 Compound mixing several entities of those types.</li>
311 <li> The attractor doesn't have to be a sub-shape of the shape to mesh.</li>
312 <li> The size will grow exponentially (see the formula below) but is
313 bounded by gradation, \n so if you want the formula to be strictly
314 respected, you should set the <i>gradation</i>
315 to its maximum (2.5) in the <i>arguments</i> tab.
318 <li> Furthermore you can choose to <i> keep the size constant </i>
319 until a certain distance from a shape. This option can be combined or
320 not with an <i>attractor</i> size map described above.
322 <li> If the two options are combined the size will remain constant
323 until the distance specified in "constant over" and grow then as
324 prescribed by the attractor function.</li>
325 <li> Else the growing is only controled by the standard arguments of
326 BLSURF (gradation ...).</li>
330 \image html blsurf_attractors2.png "Example of mesh created using
331 attractors, the attractors here are the side edges and the size grows
332 from the side of the surface towards the apex"
334 \image html blsurf_const_size_near_shape2.png "Example of size map
335 with constant size option, the size is kept constant on the left side
336 of the surface until a certain distance"
338 Remark : The validation of the hypothesis might take a few seconds if
339 attractors are defined or the "constant size" option is used because a
340 map of distances has to be built on the whole surface for each face
341 where such a hypothesis has been defined.
343 <br><b>See Also</b> a sample TUI Script of the \ref tui_blsurf "creation of a BLSurf hypothesis", including size map.
345 \anchor blsurf_attractor_computation
346 <h2>Computation of attractors</h2>
348 The size grows exponentially following the equation :
349 \f$h(d) = \mathrm{User Size} + (\mathrm{h\_start} - \mathrm{User Size}) \times e ^ { - \left( \frac{d}{R} \right) ^ {2} }\f$
353 <li>h_start is the desired size on the given attractor shape</li>
354 <li>d is the distance of the current point from the attractor
355 shape. The distance is the geodesic distance (i.e. calculated by following the surface to be meshed) </li>
356 <li>R is called the distance of influence and allows controlling the growth rate of the mesh </li>
359 <h1>Custom enforced vertices</h1>
361 \image html blsurf_parameters_enforced_vertices.png
363 It is possible to define some enforced vertices to BLSurf algorithm
364 without creating any vertices by CAD algorithms.
366 <li>The enforced vertex is the projection of a point defined by its
367 (x,y,z) coordinates on the selected face.</li>
368 <li>It is possible to define several enforced vertices on a face or a group of faces.</li>
369 <li>If the projected point is on the boundary or outside of the face, it will be ignored.</li>
372 <br><b>See Also</b> a sample TUI Script of the \ref tui_blsurf "creation of a BLSurf hypothesis", including enforced vertices.
376 Currently BLSURF plugin has the following limitations.
378 <li>BLSURF algorithm cannot be used as a local algorithm (on
379 sub-meshes) or as a provider of a low-level
380 mesh for some 3D algorithms, because the BLSURF mesher (and
381 consequently plugin) does not provide the information on node
382 parameters on edges (U) and faces (U,V). For example the
383 following combinations of algorithms are impossible:
385 <li> global MEFISTO or Quadrangle(mapping) + local BLSURF;</li>
386 <li> BLSURF + Projection 2D from faces meshed by BLSURF;</li>
387 <li> local BLSURF + Extrusion 3D;</li>