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

Roman Fratczak fratczakroman at o2.pl
Wed Mar 12 18:45:53 CET 2014

```Steffan,

There are only lines & points. Where are the surfaces and volume definition?
See -> Line loop () ...etc
then -> Plane Surface () = { ...etc
then -> Volume () = { ... etc.

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
>>>
>>> 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
>>>>>     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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>

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