# (FD WENO) Correct symmetry boundary condition for Euler equations

I'm trying to solve 2D Euler equations in axisymmetric formulation with finite-difference WENO scheme. I found some info on high-order boundary conditions for plane formulation (in this thesis, for example: 1), but couldn't find info on axisymmetrical case.

What is the correct way to implement symmetry condition at the axis $$r=0$$? Should we use ghost cells with $$r<0$$ and how to do so? Should the axis go through cell centers or in between the centers?