[Gmsh] Gmsh how to extract the node ID's on a given 3D Mesh Boundary Surface

[G. D. McBain]

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
Le 17 juin 2018 7:12 PM, Zuheyr Alsalihi <zuheyr at gmail.com> a écrit :

> Is there a way to get the node ID's of  the elements that lie on a boundary surface in a 3d solid mesh where I mark the surface by creating a physical surface.

I don't know how to do that directly in Gmsh, but for a (two-dimensional) example using Python to extract the nodes belonging to different Physical Lines, see

    https://github.com/kinnala/scikit-fem/blob/master/examples/ex14.py

The essential line is the dict-comprehension on line 52:

    boundaries = {bc:
                              np.unique(cells['line'][cell_data['line']['gmsh:physical'] ==
                                                                    field_data[bc][0]])

                               for bc in field_data if field_data[bc][1] == 1}

basically having loaded the mesh from Gmsh into Python with meshio, this filters the element-node connectivity array according to the Physical boundary entities, and then applies numpy.unique to each subset.
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