Hi John,
At the PR hangout, we discussed the possibility of eventually creating a method to extract subsets of AMR hierarchies that would include only grid patches that are at least partially contained within the data container. With them, we would also include the mask arrays to be applied to each grid patch such that you would only get the cells within the container. However, this was deemed something that should not hold up this PR, but that could eventually subbed in to fill in any gaps in functionality created by treating the grid data like particles. We decided that patching the existing machinery with a frontend-specific cell_volume field was the best thing as it would get this on front of users faster, especially since it contains a lot of other things that are fully working. I may have missed some important parts of the discussion, but my memory faded a lot faster than I thought it would.
I probably won't have much time to work on this until Friday, but I'll try to play around with the derived quantities when I can.
Britton