[Gmsh] bad orientation

[Ugis Lacis]

Dear Jose,

I think I have had similar error, when importing GMSH mesh into 
FreeFEM++, few years ago (although it seems that the error message might 
have changed). It turned out that the direction of loop definition in 
GMSH was the issue for me. See below my exchange with FreeFEM++ mailing 
list.

Maybe it can be helpful for you.

Best regards,
Ugis Lacis
Researcher
KTH Mechanics

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-------- Forwarded Message --------
Subject: 	Re: [Freefempp] Issue with loading mesh from GMSH.
Date: 	Fri, 3 Aug 2018 09:41:29 +0200
From: 	Uģis Lācis <ugis.lacis at gmail.com>
To: 	FreeFem mailing list <freefempp at ljll.math.upmc.fr>



Hi everyone,

I managed to solve the issue myself. It turned out that the direction of 
GMSH loop was surviving till FreeFEM++ and while GMSH did not complain 
about anything, FreeFEM++ couldn't use the mesh. mesh2 could be fixed by 
changing signs in all lines within the line loop, i.e.,
change
Line Loop(5) = {18, 19, 20, 12, 7, 8};
to
Line Loop(5) = {-18, -19, -20, -12, -7, -8};

Maybe this helps to someone at some point.

Best,
Ugis

On 02/08/18 15:30, Uģis Lācis wrote:
Dear FreeFEM++ users and developers,

I have run into an issue which I am unable to solve by myself. I have 
been using FreeFEM++ together with GMSH without any problems for quite 
some time. Now, however, trying to load a 2D mesh generated by GMSH, 
gives me following error:

Assertion fail : (area>0)
     line :281, in file ./include/fem.hpp

I attach the corresponding geo and msh files of two meshes (mesh1 - 
working fine, mesh2 - does not load), as well as edp file for reading 
and plotting the mesh.

I have carefully checked that physical tags are applied correctly, I 
have tried exporting both in MSH and MESH (medit) formats, using GMSH 
versions 3.06 and 2.16.0, as well as using FreeFEM++ versions 3.560000 
and 3.610002, all try has led me to the same behaviour. I have 
identified that the issue comes from the surface mesh, if I export only 
line mesh (comment out "Physical Surface(11) = {3,4};" from mesh2.geo 
and run "gmsh -2 mesh2.geo"), then it loads fine. But checking the mesh 
within GMSH, everything seems to be perfectly fine...

Do you have any suggestions on how to solve this issue?

Best regards,
Ugis Lacis
Researcher
KTH Mechanics
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On 14/05/2020 12:03, Jose Juan Alonso del Rosario wrote:
> Dear colleages
>
> I am trying to build the mesh for a slice with a pentagonal hole.
> GMSH runs properly with good quality tets but when trying to read it 
> from freefem++ the error is:
>
> " Bad orientation: The adj border element  defined by [  16 246 ]  is 
> oriented in the same direction in element 3922 and in the element 446 
> ****** bug in mesh construction? orientation parameter?
>   current line = 12 mpirank 1 / 2
> "
> Can you give any advice on this?
>
> Thanks in advance
>
> Jose
>
> -- 
> Prof. Dr. Jose Juan Alonso del Rosario
> Applied Physics Dept.,
> Naval and Oceanic Engineering.
> University of Cadiz.
> Avda Rep Saharaui s/n. Puerto Real, 11510, Cadiz, Spain
> Tlf: +34 956 016054
> Fax: +34 956016079
> Secretary: +34 956016078
>
> "All I wanna say is that they don't really care about us", Michael Jackson
>
> _______________________________________________
> gmsh mailing list
> gmsh at onelab.info
> http://onelab.info/mailman/listinfo/gmsh

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