[Gmsh] Error : Self intersecting surface mesh, computing intersections (this could take a while)
Steffen Becker
steffenbecker87 at yahoo.de
Wed Mar 12 10:17:47 CET 2014
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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