[Gmsh] Intersecting facets, -d switch

[=?windows-1252?Q?Jean-Fran=8D=E7ois_Remacle?=]

Blacker, Nalini(Contractor) a écrit :
>
> When attempting to create a 3D mesh in a volume defined from a .stl 
> surface mesh (fairly coarse, not optimal cell distribution), I receive 
> the error below. A few questions:
>
> 1) Are the intersecting faces related to the 'identical verts' warnings?
>
> 2) What is the -d switch and how do I use it? .. I haven't been able 
> to find any mention of this anywhere.
>
> 3) Are the facet numbers listed with their geometric definition 
> somewhere? My .stl file doesn't seem to have facet numbers, only their 
> geometric definitions. I don't really want to count to the 6770th one 
> if I can help it!
>
> 4) What are the numbers used to describe the intersecting subfaces? 
> Node numbers? Are they recorded in a file somewhere?
>
> Thanks,
> Nalini
>
> [nalini at flightlab ~/gmsh]$ gmsh mrh90-mod5.geo -3
> Info    : Increasing process stack size (10240 kB < 16 MB)
> Info    : 'gmsh mrh90-mod5.geo -3 ' started on Mon Nov 12 16:04:35 2007
> Info    : Reading 'mrh90-mod5.geo'
> Info    : Reading 'mrh90-mod12.stl'
> Info    : 10542 facets
> Info    : Read 'mrh90-mod12.stl'
> Info    : Read 'mrh90-mod5.geo'
> Info    : Meshing 1D...
> Info    : Mesh 1D complete (0 s)
> Info    : Mesh
> Info    : Meshing 2D...
> Info    : Mesh 2D complete (0 s)
> Info    : Mesh
> Info    : Meshing 3D...
> Info    : Meshing volume 3 (Delaunay)
> Constructing Delaunay tetrahedralization.
> Delaunay seconds:  0.68
> Creating surface mesh.
> Warning:  Polygon 1 has two identical verts in facet 6770.
> Warning:  Polygon 1 has two identical verts in facet 6785.
> Warning:  Polygon 1 has two identical verts in facet 6790.
> Warning:  Polygon 1 has two identical verts in facet 6797.
> Perturbing vertices.
> Delaunizing segments.
> Constraining facets.
> Error:  Invalid PLC.
>   Two subfaces (2969, 2968, 5427) and (10977, 12303, 12831)
>   are found intersecting each other.
>   Hint:  Use -d switch to find all intersecting facets.
> terminate called after throwing an instance of 'int'
> Abort
>
>
It seems that your stl file has facets that self intersect. In the case 
of a real CAD model,
gmsh can repair the surface mesh and restart the 3D mesh. For a STL, it 
is more problematic.
In the nightly version, I have added a more comprehensive error message, 
comuting all intersections
and telling all vertices and faces that have such problem.

JFR


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