[yt-users] Projection questions

[Scott Feister]

Hi Nathan,

Thanks a lot for the clarifications. I got confused on just one of your
sentences:

*It will average all the cells along the line of sight at that x,y value.
Those cells might have different spatial resolutions.*

So, a projection doesn't factor in every cell in the simulation, but it
takes some subset? So, if there is a single cell in the grid that happens
to have an absolutely enormous field value, it's quite possible that this
will be under-factored or over-factored in a projection (depending on if
the projection rays "misses" or "hits" it)?

When you say the cells might have different resolution, do you mean they
would have *sub-cells *or that they would have different
lengths/widths/heights?

Thanks a lot!

Best,

Scott




Scott Feister, Ph.D.
Postdoctoral Researcher, Flash Center for Computational Science
University of Chicago, Department of Astronomy and Astrophysics

On Tue, Oct 4, 2016 at 2:17 PM, Nathan Goldbaum <nathan12343 at gmail.com>
wrote:

>
>
> On Tue, Oct 4, 2016 at 11:26 AM, Scott Feister <sfeister at gmail.com> wrote:
>
>> Hi all,
>>
>> 1) Is there a way to do a "mean" ProjectionPlot? As far as I can tell,
>> the options are "integrate", "mip", and "sum", so I am guessing the answer
>> is no. I know you can do this with regions by reg.mean(), and make your own
>> plot in matplotlib.
>>
>
> If you use a weight field you'll get back a mean value (weighted by that
> field). If you want an unweighted mean, you can weight by the "ones" field
> (although this will likely not be what you want for AMR data). If you want
> a mass-weighted mean, you can weight by the cell_mass field. If you want a
> volume weighted mean, use cell_volume.
>
>
>> 2) If I do a Z projection on a domain with high X,Y spatial resolution,
>> will it average cells along X and Y (within the pixel limits) at each Z
>> depth as it projects? Or, just pick a single cell at X,Y for each pixel?
>>
>
> It will average all the cells along the line of sight at that x,y value.
> Those cells might have different spatial resolutions.
>
>
>>
>> Also, does anyone know if the reg.mean() function weights the cells
>> equally in the mean if there is varied spatial resolution? For example, I
>> know the reg.integrate() function multiplies by path length, but reg.sum()
>> simply adds up cell values.
>>
>
> The mean() function takes a field to weight by:
>
> http://yt-project.org/docs/dev/reference/api/generated/yt.
> data_objects.selection_data_containers.YTRegion.mean.html#
> yt.data_objects.selection_data_containers.YTRegion.mean
>
> By default it uses "ones" or "particle_ones", depending on whether you're
> averaging a particle or mesh field.
>
>
>>
>> Thanks!
>>
>> Scott
>>
>> Scott Feister, Ph.D.
>> Postdoctoral Researcher, Flash Center for Computational Science
>> University of Chicago, Department of Astronomy and Astrophysics
>>
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