[yt-users] unit conversions

[Stephanie Tonnesen]

Thanks for pointing all this out--I have no idea how I passed the points
example straight to the lines example!  I need to fiddle for a little while
and see if I can get this to give me what I want.

Thanks again!

Stephanie


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

On Mon, Jun 19, 2017 at 11:00 PM, Nathan Goldbaum <nathan12343 at gmail.com>
wrote:

>
>
> On Tue, Jun 20, 2017 at 1:00 AM, Nathan Goldbaum <nathan12343 at gmail.com>
> wrote:
>
>>
>>
>> On Tue, Jun 20, 2017 at 12:42 AM, Stephanie Tonnesen <stonnes at gmail.com>
>> wrote:
>>
>>> 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?
>>>
>>
>> Yup:
>>
>> http://yt-project.org/docs/dev/cookbook/complex_plots.html#
>> volume-rendering-with-points
>>
>> It looks like PontSource optionally takes either a scalar or ndarray of
>> radii (one radius value for each point):
>>
>> http://yt-project.org/docs/dev/reference/api/yt.visualizatio
>> n.volume_rendering.render_source.html#yt.visualization.
>> volume_rendering.render_source.PointSource
>>
>
> And the radii must be given in pixels. I guess we should probably improve
> this API to handle units better.
>
>
>>
>>
>>>
>>> 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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