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

Roman Fratczak fratczakroman at o2.pl
Wed Mar 12 09:50:45 CET 2014


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
>>>>>>
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> gmsh mailing list
>>>>>> gmsh at geuz.org
>>>>>> http://www.geuz.org/mailman/listinfo/gmsh
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> gmsh mailing list
>>>>> gmsh at geuz.org
>>>>> http://www.geuz.org/mailman/listinfo/gmsh
>>>>
>>>
>>
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.geuz.org/pipermail/gmsh/attachments/20140312/b87b34b4/attachment.html>