[Kwant] How to extract a sheet from 3D system?

Hello all, I want to know how I can extract a sheet from any 3D system, e.g. I have coded 3D BHZ model, found wavefunction inside the scattering region, I want to extract data for a sheet (e.g. y=1 surface) out of wavefunction array. But I do not know how each site is labeled. I mean, I want to know how sites are ordered or how each element in wavefunction array is related to each site of system. You can find my code here: http://nbviewer.ipython.org/urls/gist.githubusercontent.com/AliAsgharpour/99... Best regards, Ali