[yt-users] Total quantity projected over

[Matthew Turk]

Hi Elizabeth,

On Fri, Mar 15, 2013 at 5:15 PM, Elizabeth Tasker
<tasker at astro1.sci.hokudai.ac.jp> wrote:
> Hi,
>
> When you create a projection:
>
> projy_proj = pf.h.proj(2, 'Density', source=cloud)
>
> is there a way of knowing the sum of the quantity that has been integrated over? (or equally, knowing the integration depth for each cell, so the total quantity can be calculated)?
>
> I'd like to sum up the mass above a certain surface density threshold in my source, "cloud". From the above, projy_proj will tell me which regions of my cloud are above a threshold, but I can't think of an easy way to know how much mass has been summed over in that cell.
>
> projy_average = pf.h.proj(2, "CellMass", weight_field="Ones", source=cloud) will give me an average, but not a total.

You could sum up the cell sizes:

(proj["pdx"] * 2.0)**2.sum()

Note that pdx is half-widths, so we multiply by two.  This will need
to be unit-converted from code to whatever.

-Matt

>
> Elizabeth
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