How can I determine the orientation of normals on a given grid?"

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Hi all,
I have a grid grid = bempp.api.shapes.sphere(r=0.5, origin=(0, 0, 0), h=0.2) and I want to obtain the swapped normals .

Any help is highly appreciated.
Thanks a lot!

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Hi Chayma,

You can obtain the normals of the grid with grid.normals, which are the unit-sized normal vectors at each triangular element.

You can check the orientation of the normals by exporting the grid and opening it in Gmsh.

There is no built-in functionality to swap the orientation of the normals. A workaround would be creating another grid with an opposite triangle orientation, e.g., grid_swapped = bempp.api.Grid(grid.vertices, grid.elements[[0,2,1],:]), where the order of the element indices are changed.

Be aware that Bempp assumes that the user defines the grid with consistent normal orientation.

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Dear Elwin,

Thank you very much for your reply.
I used also swapped_grid=bempp.api.grid.grid.union([grid], swapped_normals=len([grid])*[True]).
Best,
Chayma.