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.


On Mon, Oct 26, 2015 at 9:45 PM, John ZuHone <jzuhone@gmail.com> wrote:
Hi all,

Matt asked someone to send a quick note about the current issues regarding the ytdata frontend PR:


I’m sending it because I’m working on it currently, but I was not able to attend today’s PR hangout so anyone else who was more to add or to correct should chime in. 

Currently, there are 3 issues, from most important to least important:

1. Tests don’t work
2. Doesn’t support Python 3
3. Derived quantities don’t work

I’m currently working on 1 and 2, and there have been some ideas about 3. The main issue with the latter is that for non-gridded data containers (like sphere, disk, etc.) created from grid datasets, we treat the new datasets as “particle data”. For that reason there is an issue with calculating the cell_volume properly. Without that, we cannot use the total_mass() quantity. Given that we have the cell deltas in the dataset, we could have a special derived field for the cell_volume. 

There are other issues with some of the other derived quantities (e.g., weighted_average_quantity returning the wrong units), but I haven’t been able to diagnose them yet. 

I’m working on some changes that will need to be merged into Britton’s fork eventually to address at least 1 and 2.



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