Extraction of Neumann boundary

Hello all,

My Problem is: I want to calculate both dirichlet-to-neumann maps and neumann-to-dirichlet maps.
However I fail to reconstruct the values of the neumann boundary from the solution.
If you guys know how the problem gets the neumann boundary in the first place, maybe you can give the hint on how to extract a neumann boundary properly.
Basically for defining Neumann boundary conditions I do something like this:
```julia
Ω = Triangulation(mesh)
dΩ = Measure(Ω,2)
Γ = BoundaryTriangulation(mesh, tags= "boundary" )
dΓ = Measure(Γ,2)
# Weak problem:
a(u, v) = ∫( γ * ∇(v) ⋅ ∇(u) )dΩ
l(v) = ∫( b * v )dΓ #here it gets the Neumann condition
```
But there is no extract neumann boundary function.
And sofar all my experiments on extracting it have failed. My input differs from my output.
Like this:

I know how to calculate the gradient at a given point, but I don't know exactly how the "normal" vector for each boundary point is calculated.

Start with the BoundaryTriangulation and Measure calls in the Julia example, then review how the weak problem's boundary term handles the Neumann condition. Investigate how boundary normals and gradient values are represented. Done would require a documented, reproducible way to recover Neumann boundary values, but the issue names no file or test.

Written by the indexing model from the issue text.