Hi Andre - Thanks for the detailed report. One solution will definitely be to post-process (optimize) the mesh, as currently we just leave it as is. Optimization will be available pretty soon.
On 04 Feb 2013, at 21:30, Andre Nicolle <[email protected]> wrote: > Hi Christophe > > Thank you for revisiting this issue. It is helpful to know that it is > possibly not just an implementation problem. I have retried the mesh of the > human STL. Summarising, the problem does not seem to have gone away with the > latest version of gmsh. I tried both the self built svn version and the > nightly build from the website (64bit) on the 2/2/2013 and found no > difference between them. As a way of determining if there was any particular > problem I also did a quick parameter study using different meshing algorithms > "Mesh.Algorithm" and partitioning methods "Mesh.RemeshParametrization". in > all cases the resolution was set to "Mesh.CharacteristicLengthFactor=0.05" > which produces a 2d surface mesh of around 80,000 triangles. > > As before the partitioning is around the waist line of the human as shown in > the file attached error_partition.jpg. The meshing algorithm we had the most > success with was the "Frontal" where the elements were evenly spread as can > be seen in the attached files face_q.jpg and face_mesh.jpg. > > I have found that Delaunay or MeshAdapt options have difficulty meshing > around the human limb extremities such as the feet. The example file attached > frontal_foot.jpg shows a good quality mesh which can be produced at any > resolution. When using Delaunay or MeshAdapt I found that the elements get > substantially coarser around relatively sharp edges as can be seen in file > meshadapt_foot.jpg. This problem gets worse as the resolution is increased. > > I have also tried each of the seven RemeshParametrization as I was interested > to see the effect of this parameter. It seems that options 7,1 both do not > have bad elements around the partition regardless of the mesh resolution. > However the problem with these options the arms and feet get cut off as can > be seen in file mis_feet.jpg. This occurs regardless of the meshing algorithm. > > The only RemeshParametrization option where this does not happen is 4,5 > however both algorithms suffer from poor elements on the partition region. > > I hope this information helps in some degree in solving the problem we are > encountering. If I can help any further please let me know. > > Thanks > > Andre > > On 01/02/2013 01:14, Christophe Geuzaine wrote: >> Hi Andre - Could you try again with a recent build and tell us if things >> improved? >> >> Thanks, >> >> Christophe >> >> On 31 Oct 2012, at 06:18, Andre Nicolle <[email protected]> wrote: >> >>> Dear gmsh user group >>> >>> I have been struggling with meshing a stl file of a human mesh. The stl >>> surface is in good shape with a closed surface which when loaded into gmsh >>> and meshed using the procedure outlined in >>> https://geuz.org/trac/gmsh/wiki/STLRemeshing forms a three-dimensional >>> mesh. Unfortunately the tetrahedron element quality is very poor. On >>> further investigation we found that this was caused by poor quality >>> elements on the 2D surface after the surface was remeshed. We tried using >>> Mesh.Algorithm: 1 = MeshAdapt, 2=Automatic, 5=Delaunay, 6=Frontal and found >>> that in general Frontal gave us the best elements which were all very good >>> quality except on the interface between the multilevel mesh partitions. >>> Information on the partition stage of 2-D meshing is given below. >>> >>> Attached is a picture showing the line-up of poor quality elements around >>> the waist of the human. Nearly all the other 2-D triangular elements have a >>> mesh quality indicator gamma > 0.5, however elements on theinterface have >>> gamma approximately 0.03 which we believe is where the 3-D mesh problem is >>> starting from. >>> >>> Could somebody give us some advice on how best to solve this problem as I >>> imagine it is a mistake on our implementation. If further information is >>> required please let me know what would be helpful to diagnose the problem. >>> >>> Any help would be gratefully received >>> >>> Andre >>> >>> gmsh version 2.6.1 >>> >>> Info : Meshing surface 200 (Compound surface, MeshAdapt) >>> Warning : Wrong topology: Genus=0, Nb boundaries=0, AR=1 >>> Info : ----------------------------------------------------------- >>> Info : --- Split surface 200 in 2 parts with Multilevel Mesh partitioner >>> Info : Building graph... >>> Info : Partitioning graph... >>> Info : Launching Chaco graph partitioner >>> Info : Done partitioning graph >>> Info : *** Mesh partition: level (1-0) is ZERO-GENUS (AR=5, NB=1) >>> Info : *** Mesh partition: level (1-1) is ZERO-GENUS (AR=4, NB=1) >>> Info : Multiscale Partition SUCCESSFULLY PERFORMED : 2 parts (3.26 s) >>> Info : *** Starting parametrize compounds: >>> Info : Parametrize Compound Line (2) = 1 discrete edge >>> Info : Parametrize Compound Surface (203) = 201 discrete face >>> Info : Parametrizing surface 203 with 'convex map' >>> >>> >>> Warning : Mesh generation error summary >>> Warning : 1 warning >>> Warning : 0 errors >>> Warning : Check the full log for details >>> >>> >>> <test.jpg>_______________________________________________ >>> gmsh mailing list >>> [email protected] >>> http://www.geuz.org/mailman/listinfo/gmsh > > <error_element.jpg><error_partition.jpg><face_mesh.jpg><face_q.jpg><frontal_foot.jpg><meshadapt_foot.jpg><mis_feet.jpg> -- Prof. Christophe Geuzaine University of Liege, Electrical Engineering and Computer Science http://www.montefiore.ulg.ac.be/~geuzaine _______________________________________________ gmsh mailing list [email protected] http://www.geuz.org/mailman/listinfo/gmsh
