Getting position data for fields

[DerekK44]

Hello!
Is there a way of getting the exact (x,y,z) position for each element in the numpy arrays returned for functions like ms.get_dfield(band)?

Ideally, something like the get_array_metadata() function implemented in MEEP. Right now I am linearly interpolating from the min <-> max values of the simulation region, but this seems to be shifted off by a fraction of a pixel or so.

Let me know if I can clarify my question.

Thanks!

[stevengj]

Suppose you have 3 lattice vectors (R₁,R₂,R₃), and the number of points in each direction are (N₁,N₂,N₃). Then for a given pixel indexed by (i₁,i₂,i₃) where iₖ runs from 0 to Nₖ-1, the corresponding Cartesian coordinate vector is (i₁/N₁ - ½) × R₁ + (i₂/N₂ - ½) × R₂ + (i₃/N₃ - ½) × R₃.

Right now I am linearly interpolating from the min <-> max values of the simulation region, but this seems to be shifted off by a fraction of a pixel or so.

This will be off because of the periodicity — the min and max coordinates are actually the same point and it is not stored twice. Hence the last pixel is actually slightly before the max.

[DerekK44]

Thank you. This answers my question exactly.