Add units to simulation results files

Problem

I'm working on adding simulation result visualization to 3D Slicer and what I am missing is a way to reliably determine the unit system (cgs, mm-g-s, mm-kg-s, ...), units of each quantity (e.g., speed: cm/s or length/time), and other metadata (such as anatomical coordinate system convention - LPS or RAS). Units are not only for labeling but for data transformation: we need to convert mesh point coordinates and all quantities to mm based unit system, as mm is used for all clinical imaging.

Currently, we need to manually specify coordinate system and unit system and use some heuristics based on array names to figure out how to scale them, but it is quite fragile. Could you add field data arrays to specify these information?

Solution

Save unit system, units for each point/cell array, and additional metadata (such as anatomical coordinate system) in the output mesh.

Additional context

It would be nice if this could become a commonly used standard across different solvers.

Code of Conduct

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The issue names no files, tests, or entry points. Start by locating where output meshes and field-data arrays are written, then inspect how simulation result files represent point and cell quantities. Done means the output includes the unit system, units for each array, and additional metadata such as anatomical coordinate conventions.