[Gmsh] host elements on boundary for unit normal computation

[Danny Lathouwers - TNW]

Dear gmsh users,

 

I have recently started to use gmsh for my purposes (radiation
transport). I encounter the following rather general issue: My own FEM
code reads a mesh file with the internal element information and
boundary element information consisting of a list of host internal
element and its face that makes up the boundary. From the latter I can
then extract the unit normal and compute the required integrals. I
therefore need to convert the mesh file from gmsh to my own format.

 

In the gmsh format the boundary elements are listed (if needed) with the
associated nodes. I could of course easily search the Element list to
see to what elements the boundary elements belong and which face it is
but this seems an expensive operation (work scales with the square of
the mesh size I suppose). 

 

It seems to me you always need to find the host element to figure out
the unit normal as the sign of it is otherwise unknown. Is this the
proper way of doing things or is there a cleverer alternative?

 

Thanks and best regards.

Danny Lathouwers.

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