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

j s oishi jsoishi at gmail.com
Mon Dec 16 07:50:31 PST 2013


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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