[Gmsh] Meshing algorithms and suggestions

[Guilherme Saturnino]

Dear Christophe,

/I would recommend using the default one.
/

/(Is the quality of the STL meshes sufficient, or do you need to remesh 
them?)/

We have several steps of cleaning, smoothing and and re-sampling 
surfaces before volume meshing in GMSH. We actually want to do 
"curvature-weighed re-sampling". That is, we want to re-sample our 
surfaces but keep the node density higher where the mesh is more curved. 
Do you know of any algorithm that can do that?

/Recent Gmsh versions optimize automatically. We will introduce some 
fine-tuning in the future to change the speed/quality tradeoff ; 
currently a good compromise is hardcoded.
/

Looking forward to it! When we create our meshes, we still notice a few 
bad-shaped elements. Is it because of the surfaces? How do the surfaces 
constrain the volume meshing and optimization?

/The official Linux binaries are compiled on the "old-stable" Debian, in 
order to support even quite old Linux distributions. Can you share the 
error you get on CentOS 6 ?
/

I get

gmsh-4.0.1-Linux64/bin/gmsh: /usr/lib64/libstdc++.so.6: version 
`GLIBCXX_3.4.14' not found (required by gmsh-4.0.1-Linux64/bin/gmsh)
gmsh-4.0.1-Linux64/bin/gmsh: /usr/lib64/libstdc++.so.6: version 
`CXXABI_1.3.5' not found (required by gmsh-4.0.1-Linux64/bin/gmsh)
gmsh-4.0.1-Linux64/bin/gmsh: /usr/lib64/libstdc++.so.6: version 
`GLIBCXX_3.4.15' not found (required by gmsh-4.0.1-Linux64/bin/gmsh)

CentOS 6 comes with an old glibc version, and updating it is not 
trivial. Compiling gmsh on a CentOS 6 VM should solve this issue

/Yes, that's indeed in our plans for a future revision of the MSH4 
format, together with even better handling of very large meshes/datasets./

Nice!

By the way, I was implementing an I/O function for version 4 binaries 
and I believe I found a mistake in the documentation:

"numNodes" in the blocks of both $Nodes and $Elements seems to be an 
int, unsigned long. I also found that I need to skip 4 bytes after each 
block header.


Best Regards,

Guilherme


On 09/12/2018 10:32 PM, Christophe Geuzaine wrote:
>
>> On 12 Sep 2018, at 14:31, Guilherme Saturnino <guilhermebs at drcmr.dk> wrote:
>>
>> Dear Gmsh developers,
>>
>> I'm working on a package called SimNIBS (http://simnibs.org/) that does FEM simulations in human head models. We use gmsh to create tetrahedral meshes from stl surfaces of brain and other tissues. Is there any particular meshing algorithm you would suggest for this application?
> I would recommend using the default one.
>
> (Is the quality of the STL meshes sufficient, or do you need to remesh them?)
>
>
>> What about optimization algorithms? We prefer robustness and quality over speed.
> Recent Gmsh versions optimize automatically. We will introduce some fine-tuning in the future to change the speed/quality tradeoff ; currently a good compromise is hardcoded.
>
>> I would also like to suggest 2 improvements for future Gmsh versions:
>>
>> 1. Is it possible to provide Gmsh 4 binaries that are compatible with CentOS 6? It is an old but still widely used Linux distribution. This has been holding us back in adopting Gmsh 4.
> The official Linux binaries are compiled on the "old-stable" Debian, in order to support even quite old Linux distributions. Can you share the error you get on CentOS 6 ?
>
>> 2. Would it be possible in future releases to have more flexible data types in $NodeData and $ElementNodeData? I think it would be very useful to store single-precision floats (to save space) or integers (to have additional labels for elements and nodes) .
> Yes, that's indeed in our plans for a future revision of the MSH4 format, together with even better handling of very large meshes/datasets.
>
> Thanks for the feedback,
>
> Christophe
>
>
>>
>> Thanks a lot for putting so much time and effort into making this great piece of software.
>>
>>
>> Best Regards,
>>
>> Guilherme Saturnino
>>
>>
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> —
> Prof. Christophe Geuzaine
> University of Liege, Electrical Engineering and Computer Science
> http://www.montefiore.ulg.ac.be/~geuzaine
>
> Free software: http://gmsh.info | http://getdp.info | http://onelab.info
>

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