[yt-users] unit conversions

Stephanie Tonnesen stonnes at gmail.com
Mon Jun 19 22:42:57 PDT 2017


Hi Nathan (and yt-users),

Thanks!  Yes,
arr_in_cm = ndarray_in_centimeters * cm

got yt to see that I was talking about cm.

The problem is that I still don't see the points.  Is there any example of
putting points on a volume rendering?  I am trying to mix the "Volume
Rendering with Lines" cookbook recipe with the PointSource api description,
but am not sure what I am hoping my result will look like--for example, how
big can I expect my points to be?  Is that something I can set?

Thanks,

Stephanie




--
Dr. Stephanie Tonnesen
Alvin E. Nashman Postdoctoral Fellow
Carnegie Observatories, Pasadena, CA
stonnes at gmail.com

On Mon, Jun 19, 2017 at 5:48 PM, Nathan Goldbaum <nathan12343 at gmail.com>
wrote:

> Hi Stephanie,
>
> If you have a loaded dataset, you can convert an ndarray that you know is
> in centimeters to a YTArray in code_length units like so:
>
> arr_in_code_length = ds.arr(ndarray_in_centimeters, 'cm').to('code_length')
>
> In addition, I don't think you actually need to convert to code_length
> units if you are passing this array to yt, since yt will internally do the
> conversion if you hand it a YTArray with units, so just creating an array
> like this is sufficient:
>
> from yt.units import cm
>
> arr_in_cm = ndarray_in_centimeters * cm
>
> And then pass arr_in_cm to some yt function.
>
> If all you want is the conversion factor from CGS to code length units,
> then you can inspect ds.length_unit. For example, the conversion from code
> length units to CGS is ds.length_unit.in_cgs(). There are a number of unit
> attributes that are attached to datasets (ds.mass_unit, ds.velocity_unit,
> ds.pressure_unit) that are useful for this sort of thing.
>
> Hope that helps!
>
> -Nathan
>
> On Mon, Jun 19, 2017 at 7:38 PM, Stephanie Tonnesen <stonnes at gmail.com>
> wrote:
>
>> Hi yt-users!
>>
>> I have what I think should be a relatively simple question.  I am trying
>> to make a 3D image of a region of a cosmological simulation, and plot
>> points in the image.  I define my region with box(left_edge,right_edge)
>> where left_edge and right_edge are in code units.  However, the points that
>> I read in from an earlier file are in cgs units.  Since the file was
>> written using yt output, I would like to just let yt do the conversions,
>> but nothing has units attached.  I want the 3d image to get everything into
>> the same units.  I feel like there are a few ways I could fix this
>> problem--1)  tell yt that my points are in cgs units, 2) force the
>> create_scene to be in cgs units, 3) get yt to tell me the conversion factor
>> from code units to cgs units.
>>
>> Unfortunately, I don't know how to do any of these things!
>>
>> Can someone give me some advice on what to do here?
>>
>> Thanks!
>>
>> Stephanie
>>
>> --
>> Dr. Stephanie Tonnesen
>> Alvin E. Nashman Postdoctoral Fellow
>> Carnegie Observatories, Pasadena, CA
>> stonnes at gmail.com
>>
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>>
>
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