Translate physical names from Gmsh meshes to PorePy tags.

[pschultzendorff]

Gmsh meshes often come with physical names/tags assigned to cells, faces, and nodes. An example is the SPE11 benchmark, which features 7 different facies with varying permeability and porosity. Translating physical names to pp.Grid.tags during meshing allows to easily implement such simulations from the Gmsh file instead of having to tediously loop through all cells and figure out which facies they belong to.

Currently, fracs.msh_2_grid translates physical names to tags only for boundary faces and only for 2D grids. This issue aims to add analogous functions for all faces, cells, and nodes for grids of all dimensions.

ToDo:

• Understand how Gmsh meshes logically translate to PorePy grids. Perhaps not all physical names are relevant for PorePy, perhaps there exists another type of "tags" in Gmsh other than physical names, etc.
• Update all methods in fracs.msh_2_grid to translate physical names into cell, face, and node tags.
• Add methods remove_tags and all_cell_tags to utils.tags. In particular the former is important, if one wants to import a Gmsh mesh but slightly alter the assignment of tags!
• The translation from physical names to tags for boundary faces in fracs.msh_2_grid.create_2d_grids is rather old and obtuse, and marked as such. Check whether this can be made clearer.

[keileg]

@pschultzendorff: Do you use meshio for reading the tags? That should take care of most of the I/O technicalities.

[pschultzendorff]

@keileg Yes, that is done by PorePy and the required information is actually stored as a variable at some point. However, when creating the subdomains, this information gets lost. See the following flowchart: