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

Steffen Becker steffenbecker87 at yahoo.de
Tue Mar 18 21:41:34 CET 2014


Hi,
puh, that's weird:
First I checked my triangles if their area is > 0 (to get the ones which 
are aligned). This didn't helped as I said in my last mail. Now I (just 
for fun) checked if the area > 0.000000001 and now it works - but I 
don't know why this is such a difference?!

Anyway, thanks for your help!
Steffen

Am 18.03.2014 10:57, schrieb Zenker, Dr. Matthias:
>
> Hi Steffen,
>
> there are still ill-defined triangles, e.g. 2319, 2320, 2321. You can 
> find that out by yourself by inspecting your mesh with gmsh in the way 
> I described in my last mail.
>
> Remark: checking "surface faces" can help to examine the surface.
>
> HTH,
>
> Matthias
>
> *Von:*Steffen Becker [mailto:steffenbecker87 at yahoo.de]
> *Gesendet:* Montag, 17. März 2014 22:39
> *An:* Zenker, Dr. Matthias
> *Cc:* Roman Fratczak; gmsh at geuz.org
> *Betreff:* Re: [Gmsh] Error : Self intersecting surface mesh, 
> computing intersections (this could take a while)
>
> Hi Matthias,
>
> thank you for your help!
> I think I successfully deleted all the triangles with zero surface. 
> Unfortunately the same error still appears (but at least with much 
> less intersections). You find my new .msh file in the appendix. Do you 
> have more ideas?
>
> Regards,
> Steffen
>
> Am 17.03.2014 11:37, schrieb Zenker, Dr. Matthias:
>
>     Hi Steffen,
>
>     I think you have ill-defined triangles in your mesh. For example,
>     there is a triangle 15328 which contains the nodes 7358, 7359, and
>     7360. But these nodes are aligned, so the triangle has zero
>     surface. I would suspect this kind of problem to be the cause for
>     the failure. I discovered that by examining your mesh after
>     merging the intersect.pos, and by displaying node labels and
>     surface labels in gmsh. I saw that this triangle was not visible,
>     just its label, and searched for "15328" in your msh file to see
>     what nodes it contains.
>
>     You should make sure that this kind of thing cannot happen when
>     you define the surface mesh.
>
>     HTH,
>
>     Matthias
>
>     *Von:*Steffen Becker [mailto:steffenbecker87 at yahoo.de]
>     *Gesendet:* Montag, 17. März 2014 11:20
>     *An:* Zenker, Dr. Matthias
>     *Cc:* Roman Fratczak; gmsh at geuz.org <mailto:gmsh at geuz.org>
>     *Betreff:* Re: [Gmsh] Error : Self intersecting surface mesh,
>     computing intersections (this could take a while)
>
>     Here it is.
>
>     Am 17.03.2014 11:14, schrieb Zenker, Dr. Matthias:
>
>         Hi Steffen,
>
>         I found out: Outlook is wrong.
>
>         I just discovered a small info saying that Outlook thinks that
>         my_file.msh is insecure and that it has deleted the attachment
>         (Grrrr). So the fault was on my side, sorry. Could you try to
>         send it again with a changed extension, e.g. rename it to
>         my_file.msh.txt?
>
>         Matthias
>
>         *Von:*Steffen Becker [mailto:steffenbecker87 at yahoo.de]
>         *Gesendet:* Montag, 17. März 2014 10:55
>         *An:* Zenker, Dr. Matthias
>         *Cc:* Roman Fratczak; gmsh at geuz.org <mailto:gmsh at geuz.org>
>         *Betreff:* Re: [Gmsh] Error : Self intersecting surface mesh,
>         computing intersections (this could take a while)
>
>         Hi Matthias,
>
>         I don't know what's wrong here.
>         When I check my mails, there is a .msh file in the mail from
>         12.03.2014 18:21 and also one in the mail from 14.03.2014 12:33.
>         Finally, I sent you again a .msh file in this mail. Do you
>         receive it?
>
>         Steffen
>
>
>         Am 17.03.2014 09:52, schrieb Zenker, Dr. Matthias:
>
>             Hi Steffen,
>
>             in the mail you mention there is only a geo file...
>
>             Matthias
>
>             *Von:*Steffen Becker [mailto:steffenbecker87 at yahoo.de]
>             *Gesendet:* Freitag, 14. März 2014 21:09
>             *An:* Zenker, Dr. Matthias
>             *Cc:* Roman Fratczak; gmsh at geuz.org <mailto:gmsh at geuz.org>
>             *Betreff:* Re: [Gmsh] Error : Self intersecting surface
>             mesh, computing intersections (this could take a while)
>
>             Hi Matthias,
>
>             hm, I sent it on 12.03.2014 18:21, don't know what went wrong.
>             As you see, I created a ASCII .msh file as explained in
>             the documentation, so I hope it's correct.
>             What can I do now?
>
>             Steffen
>
>             Am 14.03.2014 13:05, schrieb Zenker, Dr. Matthias:
>
>                 Hi Steffen,
>
>                 there was no msh file in any of your mails.
>
>                 Depending on what is in the msh file, your steps seem
>                 correct to me.
>
>                 Matthias
>
>                 *Von:*Steffen Becker [mailto:steffenbecker87 at yahoo.de]
>                 *Gesendet:* Freitag, 14. März 2014 12:33
>                 *An:* Zenker, Dr. Matthias
>                 *Cc:* Roman Fratczak; gmsh at geuz.org <mailto:gmsh at geuz.org>
>                 *Betreff:* Re: [Gmsh] Error : Self intersecting
>                 surface mesh, computing intersections (this could take
>                 a while)
>
>                 Hi Matthias,
>
>                 I think you are talking about your mail from
>                 12.03.2014 09:59 ?
>                 In one of my last mails I already sent you a
>                 selfcreated .msh file - but the 3D mesh still failes.
>                 The intersect.pos shows me some
>
>                 intersections, but when I check my nodes for
>                 duplicates I can't find any.
>                 Hope my steps are correct:
>                 - create "my_file.msh" with my python script and check
>                 it for nodes duplications -> none found
>                 - open "my_file.geo" in Gmsh
>                 - do "Modules" -> "Mesh" -> "3D"
>                 - receive error message
>                 - merge "intersect.pos" and see some intersections but
>                 I don't know why because the are no duplicated nodes
>
>                 Steffen
>
>
>                 Am 14.03.2014 09:50, schrieb Zenker, Dr. Matthias:
>
>                     Hi Steffen,
>
>                     you should be able to generate a filled volume
>                     mesh if you follow my suggestion from the other mail:
>
>                     Write  the 2D mesh in gmsh format (e.g. as
>                     outerface.msh, gmsh documentation for more info on
>                     the msh format) and merge that one instead of the
>                     myfile.ply2 file, leaving the other command lines
>                     in your .geo file as they are. If you then do a 3D
>                     mesh, gmsh will take the 2D mesh as defined in
>                     your file. You can then refine the mesh if you wish.
>
>                     HTH,
>
>                     Matthias
>
>                     *Von:*Steffen Becker
>                     [mailto:steffenbecker87 at yahoo.de]
>                     *Gesendet:* Mittwoch, 12. März 2014 20:00
>                     *An:* Roman Fratczak
>                     *Cc:* Zenker, Dr. Matthias; gmsh at geuz.org
>                     <mailto:gmsh at geuz.org>
>                     *Betreff:* Re: [Gmsh] Error : Self intersecting
>                     surface mesh, computing intersections (this could
>                     take a while)
>
>                     Hi,
>
>                     I'm so sorry for all time you spent with my
>                     problem, but now I see: We talk at cross. It's my
>                     fault, I didn't explained correctly what I need.
>                     I want to receive a *filled* volume mesh.
>                     I created 2 files (steffen.stl and steffen2.stl)
>                     with my python script.
>                     With steffen.stl I successfully could create such
>                     a filled volume mesh as seen in steffen.msh.
>                     When I try exactly the same with steffen2.stl then
>                     I get the error message in the subject (and the
>                     surface mesh doesn't get filled).
>                     So that's why the .iges file you sent me isn't
>                     what I need.
>
>                     Sorry for all this confusion,
>                     Steffen
>
>
>                     Am 12.03.2014 18:53, schrieb Roman Fratczak:
>
>                         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
>                                             <mailto: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
>
>
>
>
>
>
>
>
>
>
>                                                                         _______________________________________________
>
>                                                                         gmsh mailing list
>
>                                                                         gmsh at geuz.org  <mailto:gmsh at geuz.org>
>
>                                                                         http://www.geuz.org/mailman/listinfo/gmsh
>
>
>
>
>
>
>
>
>
>
>
>                                                                     _______________________________________________
>
>                                                                     gmsh mailing list
>
>                                                                     gmsh at geuz.org  <mailto:gmsh at geuz.org>
>
>                                                                     http://www.geuz.org/mailman/listinfo/gmsh
>
>
>
>
>
>
>
>
>
>
>
>                                                                 _______________________________________________
>
>                                                                 gmsh mailing list
>
>                                                                 gmsh at geuz.org  <mailto:gmsh at geuz.org>
>
>                                                                 http://www.geuz.org/mailman/listinfo/gmsh
>
>
>
>                                             _____________________________________________________________________
>                                             ERBE Elektromedizin GmbH
>                                             Firmensitz: 72072 Tuebingen
>                                             Geschaeftsfuehrer:
>                                             Christian O. Erbe, Reiner
>                                             Thede
>                                             Registergericht: Stuttgart
>                                             HRB 380137
>
>
>
>                     _____________________________________________________________________
>                     ERBE Elektromedizin GmbH
>                     Firmensitz: 72072 Tuebingen
>                     Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
>                     Registergericht: Stuttgart HRB 380137
>
>
>
>                 _____________________________________________________________________
>                 ERBE Elektromedizin GmbH
>                 Firmensitz: 72072 Tuebingen
>                 Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
>                 Registergericht: Stuttgart HRB 380137
>
>
>
>             _____________________________________________________________________
>             ERBE Elektromedizin GmbH
>             Firmensitz: 72072 Tuebingen
>             Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
>             Registergericht: Stuttgart HRB 380137
>
>
>
>         _____________________________________________________________________
>         ERBE Elektromedizin GmbH
>         Firmensitz: 72072 Tuebingen
>         Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
>         Registergericht: Stuttgart HRB 380137
>
>
>
>     _____________________________________________________________________
>     ERBE Elektromedizin GmbH
>     Firmensitz: 72072 Tuebingen
>     Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
>     Registergericht: Stuttgart HRB 380137
>
>
>
> _____________________________________________________________________
> ERBE Elektromedizin GmbH
> Firmensitz: 72072 Tuebingen
> Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
> Registergericht: Stuttgart HRB 380137
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.geuz.org/pipermail/gmsh/attachments/20140318/90f592b6/attachment.html>