[Gmsh] Error : Self intersecting surface mesh, computing intersections (this could take a while)

[Roman Fratczak]

Hi Steffen,

No it is more clear. If you are working with cloud of point, then you 
may use Meshlab for surface regeneration. There are many software that 
are able to handle in a resonable way the cloud of points (like rhino3D 
+ resurf, other). But these are rather commercial.

 From the other side - try to do the simplest thing:

Adjust your python script for surface creation in order to save not as 
PLY but as GMSH "geo" file using points and lines

Point(1)={0,0,0} ;
Point(2)={0,1,0} ;
...

Line(1) = {1,2};
..
and.. Line Loop & Surface -> Volume ..

Then you will get a volume defined by geometric entities. In this case 
is shoul be easier to create a better mesh on surface and then on whole 
volume.

Regards
Roman



W dniu 11.03.2014 17:59, Steffen Becker pisze:
> Hi,
>
> @ Roman:
> some more details:
> I have a point cloud given and generate the surface mesh by myself 
> (with python). I don't know a good algorithm to create a volume mesh 
> out of this surface mesh - that's why I use gmsh for this task.
> I also checked my surface mesh for double vertexes but I didn't find 
> any. What do you mean with "double egdes"? Isn't there always a 
> "double edge", because two neighbour facets always have one same edge?!
>
> I will send you a .step or .iges file as soon as I figured out how to 
> handle the "No OpenCASCADE model found" error.
>
> I'm appending the other mailing history (with Matthias) to this mail - 
> sorry for that "double mailing", I just forgot one time to "reply to 
> all" -.-
> Anyone else has an idea why the meshing fails?
>
> Regards and thank you a lot,
> Steffen
>
>
> Hi Steffen,
>
> I don't see either why the meshing fails, sorry.
>
> Matthias
>
> -----Ursprüngliche Nachricht-----
> Von: Steffen Becker [mailto:steffenbecker87 at yahoo.de]
> Gesendet: Dienstag, 11. März 2014 14:42
> An: Zenker, Dr. Matthias
> Cc:gmsh at geuz.org
> Betreff: Re: [Gmsh] Error : Self intersecting surface mesh, computing
> intersections (this could take a while)
>
> Oh I'm really sorry, here is the file.
> In addition I sent you also the intersect.pos. I don't understand why exactly
> these surfaces are problematic and the "neighbour surfaces"
> aren't - although they have the same geometry =/
>
> Am 11.03.2014 12:07, schrieb Zenker, Dr. Matthias:
> Hi Steffen,
>
> if you don't provide the myfile.ply2, we cannot see your geometry...
>   You can visualize intersect.pos by merging it to your geometry.
>
> HTH,
>
> Matthias
>
>
> Am 11.03.2014 14:33, schrieb Roman Fratczak:
>> Hello,
>>
>> It is possible, that you will get your geometry in other format?
>> In your "ply" there is already a surface mesh given. Try maybe use 
>> STEP, IGES,...  as input- then it is easer to recalculate the surface 
>> mesh.
>>
>> In case of need of usage of "a dead mesh" - maybe try first to remesh 
>> it (i.e. in blender with modification Remesh) and/or clean it 
>> (removing double vertexes and edges).
>>
>> regards
>> Roman
>>
>>
>>
>>
>> W dniu 11.03.2014 12:13, Steffen Becker pisze:
>>> Hi,
>>>
>>> in the appendix you find my model.
>>> Thanks for  help!!
>>>
>>> Regards,
>>> Steffen
>>>
>>> Am 11.03.2014 11:47, schrieb Roman Fratczak:
>>>> Hello Steffen,
>>>>
>>>> Yes. You can try to the first Optimize quality of tetra, or all of 
>>>> them (just try).
>>>>
>>>> I don't know how your model looks like. If the elements on the 
>>>> surface are too big, then the solid elements (probably tetragonal) 
>>>> may be with intersecting edges or faces. Therefore the reducing 
>>>> size of element may help (especially on the surfaces).
>>>>
>>>> Or- just share your model (ply) -in order to be more precise.
>>>>
>>>> regards
>>>> Roman
>>>>
>>>>
>>>>
>>>> W dniu 10.03.2014 18:06, Steffen Becker pisze:
>>>>> Hi Roman,
>>>>> when you say "enable option: optimize", you mean" Tools -> Options 
>>>>> -> Mesh -> Advanced -> Optimize quality of tetrahedra, Optimize 
>>>>> quality of tetrahedra with Netgen, Optimize high order meshes 
>>>>> (experimental)" ?
>>>>> And why is reducing element size important? In my case it is 
>>>>> important that the object has such "90 degree corners".
>>>>>
>>>>> Regards,
>>>>> Steffen
>>>>>
>>>>> Am 10.03.2014 16:55, schrieb Roman Fratczak:
>>>>>> Hi Steffen,
>>>>>>
>>>>>> If your volume is OK (is really a closed one) - try to:
>>>>>>
>>>>>> 1. Reduce element size (especially in a curved shapes)
>>>>>> 2. Enable option "Optimize" - in mesh options
>>>>>>
>>>>>> Regards
>>>>>> Roman
>>>>>>
>>>>>>
>>>>>>
>>>>>> W dniu 10.03.2014 16:41, Steffen Becker pisze:
>>>>>>> Hello everyone,
>>>>>>>
>>>>>>> I'm a gmsh beginner and I want to create a 3D volume mesh out of 
>>>>>>> a given surface-mesh but I got the error message as seen in the 
>>>>>>> subject. You find my .geo file in the appendix.
>>>>>>> Can anyone tell me what I have to do to create a 3D mesh? I even 
>>>>>>> can't figure out where the intersection are located (don't know 
>>>>>>> how to read the intersect.pos).
>>>>>>> Sorry for my poor english.
>>>>>>>
>>>>>>> Regards,
>>>>>>> Steffen
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> gmsh mailing list
>>>>>>> gmsh at geuz.org
>>>>>>> http://www.geuz.org/mailman/listinfo/gmsh
>>>>>>
>>>>>>
>>>>>>
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>>>>>
>>>>>
>>>>>
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>>>>
>>>
>>
>

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