CGAL users discussion list

[Matthew Russell <>]

Dear Monique,

I agree that adding points on the facets of the bounding cube in the
right places would be a way to solve this. But this technique requires
a description of the regions on each facet that should be
triangulated. This is difficult because many of the surfaces I am
dealing with are defined implicitly and do not cover the entirety of
the cube's facets. Is there something in CGAL that would help do this?

However, I suppose my actual issue is being able to accurately specify
boundary conditions. I was trying to make this easy by forcing the
boundaries of the mesh to align with bounding cube.

With a triangulation generated by the periodic mesh package, is there
a way to colour or otherwise somehow mark the cell faces on each
boundary? I'm not sure this is a meaningful question given the
irregular nature of the boundaries!

Sorry for the basic questions - I'm new to CGAL and still finding my way 
around!

Many thanks,
Matt


On Tue, 16 Mar 2021 at 10:54, Monique Teillaud
<> wrote:
>
> Dear Matthew,
>
> In fact, if you add points on the facets of the cube and you ensure that 
> the facets are triangulated as mael suggests, then you are enforcing the 
> periodicity through these points. You are not using the functionality that 
> is offered by the periodic mesh package.
> In other words, this should rather be done with the non-periodic meshing 
> package.
>
> (In fact I would be curious why you need the facets to be triangulated... 
> Our algorithm is precisely designed to avoid adding such artificial 
> points...)
>
> Best regards,
> --
> Monique Teillaud
> https://members.loria.fr/Monique.Teillaud/
> INRIA Nancy - Grand Est, LORIA
> Institut National de Recherche en Informatique et Automatique
>
> ----- Le 15 Mar 21, à 17:21, cgal-discuss <> a écrit :
>
> Hi Mael,
>
> Thanks for your reply.
>
> It's a shame the periodic mesher can't do this currently. Would you be able 
> to give some hints on how to implement your idea of using the standard 3D 
> mesh package? I'm slightly wary about manually moving vertices around - 
> won't this reduce the quality of the resulting mesh?
>
> Thanks,
> Matt
>
> On Mon, 15 Mar 2021, 08:04 Mael Rouxel-Labbé, 
> <> wrote:
>>
>> Hello,
>>
>> This is not currently possible in a straightforward manner in the
>> periodic mesh generator, as there is no 3D constrained Delaunay
>> triangulations in CGAL yet.
>>
>> In a less straight forward manner, if you wish your elements to lie
>> exactly on the boundary of the periodic domain, you might be able to do
>> away with the periodic mesh generation algorithm: generate a 3D mesh of
>> the implicit function clipped by the periodic domain, and then ensure
>> that the vertices are identical on both sides.
>>
>> Best,
>> Mael
>>
>> On 15/03/2021 02:05, Matthew Russell ( via
>> cgal-discuss Mailing List) wrote:
>> > Dear all,
>> >
>> > I would like to generate periodic 3D meshes of regions bounded by
>> > implicit functions and so I was pleased to find examples such as [1]
>> > that do almost exactly what I want. The problem that I'm having is
>> > that cells in the meshes generated from this example are able to lie
>> > across the bounding unit cube, but to use the meshes in finite element
>> > simulations I need the faces of the cells to align with the boundaries
>> > of the cube.
>> >
>> > For example, the CGAL example [1] (with a different implciit function)
>> > generates meshes like [cgal.jpg], but I would like one like
>> > [gmsh.jpg].
>> >
>> > I haven't been able to find a way to do this in CGAL. Is it possible?
>> >
>> > Many thanks,
>> > Matt
>> >
>> > [1] 
>> > https://doc.cgal.org/latest/Periodic_3_mesh_3/Periodic_3_mesh_3_2mesh_implicit_shape_8cpp-example.html
>> >
>>
>> --
>> You are currently subscribed to cgal-discuss.
>> To unsubscribe or access the archives, go to
>> https://sympa.inria.fr/sympa/info/cgal-discuss
>>
>>
>
> --
> You are currently subscribed to cgal-discuss.
> To unsubscribe or access the archives, go to
> https://sympa.inria.fr/sympa/info/cgal-discuss
>
>
> --
> You are currently subscribed to cgal-discuss.
> To unsubscribe or access the archives, go to
> https://sympa.inria.fr/sympa/info/cgal-discuss
>