[Gmsh] Error : Self intersecting surface mesh, computing intersections (this could take a while)
Roman Fratczak
fratczakroman at o2.pl
Wed Mar 12 11:48:44 CET 2014
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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