[Gmsh] dilate to flatten a mesh

[Felix Salazar]

I agree with Nathan's advice.

The source of your issue might be your geometry. If you created the surface
using gmsh, you can provide the .geo file. If you imported the surface from
CAD, there might be some spurious geometrical vertex that are forced to
belong to the triangulation, hence giving you non-zero Z components. If you
specify a Physical Surface on your .geo, it might help.

The solution of looping on your mesh file via Python (or your script
language of choice) to substitute all z by zeros is also valid.

Take care and good luck,

F

On Mon, Jun 3, 2019, 4:17 PM Nathan J. Neeteson <nneeteson at rglinc.com>
wrote:

> Hi Ricardo,
>
> If the issue is simply that you have some vertices with non-zero
> z-components, and you want them to all be zero, and if the mesh file is
> ASCII format, could you just write a script (say, in python) to
> automatically loop through the $Nodes section of the file and replace the z
> component of every vertex position with "0.0" in a new file? I don't think
> any derived geometric data (such as cell areas or volumes) is in a *.mesh
> file, so naively I would think this should work, and the script in question
> would probably be no more than a few dozen lines.
>
> Thanks,
>
> Nathan Neeteson, M.Sc., E.I.T.
> Flow Control Research Engineer
> RGL Reservoir Management Inc.
> Corporate Head Office
> P 780.851.8243 | C 613.929.6283
> nneeteson at rglinc.com | rglinc.com
> API Q1™ and ISO 9001:2015 certified facilities.
>
> -----Original Message-----
> From: Ricardo Ruiz Baier [mailto:ricardo.ruiz.baier at gmail.com]
> Sent: June 3, 2019 11:32 AM
> To: Nathan J. Neeteson <nneeteson at rglinc.com>; Ricardo Ruiz Baier <
> ruizbaier at maths.ox.ac.uk>
> Cc: gmsh at onelab.info
> Subject: Re: [Gmsh] dilate to flatten a mesh
>
> Dear Nathan,
>
> thank you very much. This indeed resolves the syntax problem. However in
> my case it does not do anything since transformations can only be applied
> to the geometry, and in this case I want to apply the dilation to the mesh.
> I'll keep looking for other solutions.
>
> All the best,
>
> Ricardo
>
> > Hi Ricardo,
> >
> > The syntax for anisotropic dilation is as follows:
> >
> > Dilate { { expression-list }, { expression, expression, expression } }
> > { transform-list }
> >
> > The first expression-list is the homethetic center of the dilation.
> >
> > The set of three expressions are the X,Y,Z scaling factors of the
> dilation.
> >
> > The transform-list is the entities to be acted on.
> >
> > I think your syntax should be:
> >
> > Dilate{ {0,0,0}, {1,1,0} }{ Point{all_points[]}; }
> >
> > Assuming you want all points on the x-y plane at z=0.
> >
> > Nathan Neeteson, M.Sc., E.I.T.
> > Flow Control Research Engineer
> > RGL Reservoir Management Inc.
> > Corporate Head Office
> > P 780.851.8243 | C 613.929.6283
> > nneeteson at rglinc.com | rglinc.com
> > API Q1(tm) and ISO 9001:2015 certified facilities.
> >
> > -----Original Message-----
> > From: gmsh [mailto:gmsh-bounces at ace20.montefiore.ulg.ac.be] On Behalf
> > Of Ricardo Ruiz Baier
> > Sent: June 3, 2019 5:51 AM
> > To: gmsh at onelab.info
> > Subject: [Gmsh] dilate to flatten a mesh
> >
> > Dear all,
> >
> > I have a .mesh triangulation which is supposed to be 2D. However it has
> some vertices with (spurious) crazy large z-components. How can I flatten
> these from e.g. a geo file?
> >
> > I've tried with "Dilate" in the manner mentioned below, but it does not
> work (the compilation complains about the syntax and I have not found any
> examples).
> >
> > Merge "testMesh.mesh";
> >
> > all_points[] = Point '*';
> >
> > Dilate { { all_points[] }, { 1, 1, 0} } {Surface(1) };
> >
> > Thank you so much!
> >
> > Kind regards,
> >
> >
> >
> > --
> > Ricardo Ruiz Baier
> > Mathematical Institute
> > University of Oxford
> > people.maths.ox.ac.uk/ruizbaier
> >
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> --
> Ricardo Ruiz Baier
> Mathematical Institute
> University of Oxford
> people.maths.ox.ac.uk/ruizbaier
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