[MOAB-dev] Boundary nodes and faces

[Tim Tautges]

[cc'ing moab-dev since it's of general interest...]

This is tricky.  As you say, if you get the local skin, that'll include interior entities shared with/ghosted from other 
procs.  If you get the skin and remove the shared entities, that'll remove the vertices that are on the geometric skin 
but also shared with other procs.  The right way to do this is:

- get the highest-dimensional entities on the skin (1d if in 2d, 2d if in 3d)
- remove any shared entities from that range (because if it's shared, then by definition there will be d+1 - dimensional 
entities on the other proc)
- if you're in 3d and you also want skin edges, get the edges adj to the entities in the range (remember the UNION arg 
on get_adjacencies), put in tmp range, then do the same for vertices, also put in tmp range
- merge the tmp range with the original range

Like I said, tricky, but welcome to parallel mesh.

- tim


On 08/14/2013 09:21 PM, Iulian Grindeanu wrote:
>
>
> ------------------------------------------------------------------------------------------------------------------------
>
>     I'm looking for a simple way to find the boundary nodes, faces and associated elements. The sidesets might not be
>     defined on these entities and so querying based on that option is ruled out.
>
>     I used the skinner to perform find_skin but this is screwy in parallel because it returns the partitions box and all
>     its parallel skin vertices and faces - not quite what I need. The geometric_skin is exactly what I need but I have
>     other problems because my GEOM_DIMENSION tag is undefined.
>
>     Thoughts ?
>
>     Vijay
>
> I am not sure I understand. After you resolve shared entities, you can filter out entities that are shared (so they are
> not on the true "skin" )
> Would that solve the problem that you have?
> You should start from boundary faces; a boundary face that is not "shared" is on the true boundary. then from there you
> can get all edges and vertices adjacent to them; they will be too on the true boundary.
>
> Iulian

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              Tim Tautges            Argonne National Laboratory
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