[yt-users] How yt deals with AMR grids and data objects

[Alex Bogert]

Yes, I misunderstood what Kern was looking for. I'm trying to do the
mapping in "real-time" on the video card. Mimicking something similar to
yt's covering grid.


On Mon, Dec 16, 2013 at 7:50 AM, j s oishi <jsoishi at gmail.com> wrote:

> As a quick follow up, Alex, the covering grid does *exactly* what you want.
>
> j
>
>
> On Mon, Dec 16, 2013 at 10:48 AM, Matthew Turk <matthewturk at gmail.com>wrote:
>
>> Hi Kearn,
>>
>> On Mon, Dec 16, 2013 at 10:23 AM,  <k.grisdale at surrey.ac.uk> wrote:
>> > Dear yt-users
>> >
>> > I am attempting to make a tool that will sample the properties of a
>> RAMSES galactic disk simulation. The tools needs to be able to work on
>> different scales going from very large (10kpc) to the very small (2x the
>> size of the smallest cell ~140pc). So far I have achieved this using data
>> objects and calling required property/Quantities that I need. On large
>> scales this works very well, however on small scales I have run into the
>> issue that only part of cells are within in my data object. While this is
>> to be expected it is presenting so interesting results. From what I can
>> tell if the centre of the cell is in my data object yt treats the cell as
>> if the whole cell is within my data object but if the centre is missed it
>> treats it as if the whole cell is absent from the data object, I’m looking
>> for a median between these extremes.
>>
>> You're right, the cell centers are used for selecting data points in yt.
>>
>> >
>> > My question is is there a way to get yt to only take into account the
>> proportion of the cell in side my data object?
>>
>> Usually they're taken into account via CellVolume weighting or
>> something along those lines.
>>
>> >
>> > Also if the cell only has small corner in my data object is there away
>> to get yt to fetch the properties of that cell (say the density and cell
>> volume) and then multiply these values by the proportion of the cell that
>> is in my object?
>>
>> The data selection won't find the cell, unfortunately, so it might be
>> somewhat tricky to do it using the standard setup.  I'd say you might
>> be interested in using a covering grid, which will expand all of the
>> cells into some higher resolution; this will enable them to be cut up
>> and subselected.  The format for this is:
>>
>> cg = pf.h.covering_grid(some_level, left_edge, dimensions)
>>
>> This will use "some_level" to determine the dx (with respect to level
>> 0) and dimensions and left edge to describe the extent.  No
>> interpolation will be conducted.  You can then select it and operate
>> on it as you like, and it will have the dict-like querying that other
>> objects do.
>>
>> -Matt
>>
>> >
>> > Thank you in advance for you help
>> >
>> > Kearn
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