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

Roman Fratczak fratczakroman at o2.pl
Wed Mar 12 18:53:50 CET 2014


Steffen,

I did a volume based on your surface mesh - see attached IGES 
(compressed with 7-zip).
After reading it into GMSH, you can create the 1D, then 2D and finally 
3D mesh with no errors.

You can do the same using GMSH volume definition (as already wrote)-> it 
will work, as the fundamental faces are plane triangles.

Regards
Roman


W dniu 12.03.2014 18:27, Steffen Becker pisze:
> Wrong .geo file, sorry!
>
> Am 12.03.2014 18:21, schrieb Steffen Becker:
>> Thank you so far,
>>
>> I create both files: .msh and .geo, but I still get the same error. 
>> What's my mistake?
>>
>> Steffen
>>
>> Am 12.03.2014 11:48, schrieb Roman Fratczak:
>>> Hi,
>>>
>>> FYI - you can remove double vertices/edges (or repair) in mesh in 
>>> FreeCad (for exampe).
>>>
>>> regards
>>> Roman
>>>
>>>
>>>
>>> W dniu 12.03.2014 10:17, Steffen Becker pisze:
>>>> Hi Matthias & Roman,
>>>>
>>>> I create a nodes- and elements-list like this:
>>>> # nodes:
>>>> N1 0,0,0
>>>> N2 0,1,0
>>>> N3 1,0,0
>>>> N4 0,0,1
>>>> # elements, which describe triangles:
>>>> E1 1,2,3
>>>> E2 2,3,4
>>>>
>>>> So I do have double edges (here: between node 2+3). Didn't now that 
>>>> this is a problem for gmsh, sorry.
>>>>
>>>> I will try Romans solution asap and give you a feedback.
>>>> Thank you both!
>>>>
>>>> Steffen
>>>>
>>>>
>>>> Am 12.03.2014 09:59, schrieb Zenker, Dr. Matthias:
>>>>>
>>>>> Hi Steffen,
>>>>>
>>>>> I am not totally sure from what you wrote that there are really no 
>>>>> duplicated nodes. In gmsh, you need to define the surfaces in a 
>>>>> way that neighbouring surfaces/facets with a common border use the 
>>>>> _/same/_ nodes to define the border. I could not see from your 
>>>>> file if there are duplicated nodes, and would propose that you 
>>>>> make sure that there are really no such duplications.
>>>>>
>>>>> If the meshing still fails, then this is a question for the real 
>>>>> gurus (Christophe?).
>>>>>
>>>>> HTH,
>>>>>
>>>>> Matthias
>>>>>
>>>>> *Von:*Roman Fratczak [mailto:fratczakroman at o2.pl]
>>>>> *Gesendet:*Mittwoch, 12. März 2014 09:51
>>>>> *An:* Steffen Becker
>>>>> *Cc:* gmsh at geuz.org
>>>>> *Betreff:* Re: [Gmsh] Error : Self intersecting surface mesh, 
>>>>> computing intersections (this could take a while)
>>>>>
>>>>> 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  <mailto: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
>>>>>
>>>>>
>>>>>
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
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>>>>>
>>>>>
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