How to read vertex boundary indicators from MSH format

[Jan Stebel]

Hi all,

I want to read a GMSH mesh consisting of line elements where the vertex at each end has set a physical number (i.e. boundary indicator in deal.II terminology). After reading the mesh file using GridIn::read_msh(), the physical numbers of vertices are lost and the vertices have boundary indicators either 0 or 1. Is there a simple way how to read the original id's?

Thanks,
Jan

[Wolfgang Bangerth]

The GridIn functions don't pass on information about individual vertices
at the moment. Can you produce a simple enough example input file that
demonstrates what you want to happen, but where this doesn't happen?
Anything that we can make into a regular testcase would be useful.

Best
W.

--
------------------------------------------------------------------------
Wolfgang Bangerth email: bang...@math.tamu.edu
www: http://www.math.tamu.edu/~bangerth/

[Jan Stebel]

On 08/24/2015 04:21 AM, Jan Stebel wrote:
>
> I want to read a GMSH mesh consisting of line elements where the vertex
> at each end has set a physical number (i.e. boundary indicator in
> deal.II terminology). After reading the mesh file using
> GridIn::read_msh(), the physical numbers of vertices are lost and the
> vertices have boundary indicators either 0 or 1. Is there a simple way
> how to read the original id's?

The GridIn functions don't pass on information about individual vertices
at the moment. Can you produce a simple enough example input file that
demonstrates what you want to happen, but where this doesn't happen?
Anything that we can make into a regular testcase would be useful.

 
A simple mesh file with line elements and two endpoints marked by physical numbers 10 (left) and 20 (right):

$MeshFormat
2.2 0 8
$EndMeshFormat
$Nodes
11
1 0 0 0
2 1 0 0
3 0.1 0 0
4 0.2 0 0
5 0.3 0 0
6 0.4 0 0
7 0.5 0 0
8 0.6 0 0
9 0.7 0 0
10 0.8 0 0
11 0.9 0 0
$EndNodes
$Elements
12
1 15 2 10 1 1
2 15 2 20 2 2
3 1 2 100 1 1 3
4 1 2 100 1 3 4
5 1 2 100 1 4 5
6 1 2 100 1 5 6
7 1 2 100 1 6 7
8 1 2 100 1 7 8
9 1 2 100 1 8 9
10 1 2 100 1 9 10
11 1 2 100 1 10 11
12 1 2 100 1 11 2
$EndElements

When processing by a code like:

  Triangulation<1,3> tri;
  GridIn<1,3> grid_in;
  grid_in.attach_triangulation(tri);
  std::ifstream input_file("l.msh");
  grid_in.read_msh(input_file);

  for (auto cell = tri.begin_active(); cell != tri.end(); ++cell)
  {
    for (unsigned int face = 0; face < 2; ++face)
    {
      if (cell->at_boundary(face))
        printf("vertex %d has boundary indicator %d\n", cell->face_index(face), cell->face(face)->boundary_indicator());
    }
  }

The result is:

vertex 0 has boundary indicator 0
vertex 1 has boundary indicator 1

I would like to have seen boundary indicators 10 and 20.

Thanks,
Jan

[Wolfgang Bangerth]

> The GridIn functions don't pass on information about individual vertices
> at the moment. Can you produce a simple enough example input file that
> demonstrates what you want to happen, but where this doesn't happen?
> Anything that we can make into a regular testcase would be useful.
>
>
> A simple mesh file with line elements and two endpoints marked by physical

> numbers 10 (left) and 20 (right): [...]

Great little testcase, thanks!

I've opened a bug report at
https://github.com/dealii/dealii/issues/1430
I hope to get to it sometime in the reasonably near future. Feel free to
subscribe to the report so that you get notified of any progress.

[Wolfgang Bangerth]

Fixed now -- thanks for the report!

[Jan Stebel]

Works! Thanks for quick fix.
Jan