# Extract normal vector data at boundary in dolfinx

**URL:** <https://fenicsproject.discourse.group/t/extract-normal-vector-data-at-boundary-in-dolfinx/13997>\
**Category:** dolfinx\
**Created:** [March 22, 2024, 3:52pm UTC](https://fenicsproject.discourse.group/t/extract-normal-vector-data-at-boundary-in-dolfinx/13997 "2024-03-22T15:52:12Z")\
**Posts on this page:** 1\
**Showing post:** 6

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**Author:** ![raboynics](https://avatars.discourse-cdn.com/v4/letter/r/4bbf92/32.png) [@raboynics](https://fenicsproject.discourse.group/u/raboynics)\
**Post date:** [March 24, 2024, 9:33pm UTC](https://fenicsproject.discourse.group/t/extract-normal-vector-data-at-boundary-in-dolfinx/13997/6 "2024-03-24T21:33:49Z")

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I see. I tested a few other tags, I guess the OP gets his answer.

However, I see in the gist the line `print(np.unique(nh.vector[:]))` where nh comes from `dfx.fem.Function(V)` rather than `n = ufl.FacetNormal(V.mesh)`.

I do not understand why `n = ufl.FacetNormal(V.mesh)` and `n.vector[:]` would not give what the OP is after.

If it’s a mesh question, why is there a need to invoke dolfinx and a FE space rather than just dealing with ufl/gmsh for example?

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