[yt-users] Field Cuts in Off-Axis Projections

[Sam Skillman]

Hi all,

I think for the idea of field cuts, the solution Kacper is the right way to
go.  Since the OffAxisProjection plots don't do vertex-centering, it should
be equivalent to doing the field cuts as a data source object.

As for going forward, HomogenizedVolume is deprecated.  For the purposes of
volume rendering arbitrary data sources, this is on my immediate todo list.
 Off-axis projections should gain the same type of functionality as that is
implemented.  The primary road block is determining exactly how the the
starting and stopping criteria should function for arbitrary data sources.
 There is a fast/easy way and a difficult/more accurate method of doing so.
 I've done the fast/easy method in a few incarnations and am ~80% happy
with it.

Sam


On Wed, Aug 7, 2013 at 2:32 PM, Cameron Hummels <chummels at gmail.com> wrote:

> Munier,
>
> I think there is a way to do what you want.  It involves using the
> HomogenizedVolume class (as opposed to the newer KDTree class) for
> decomposing the volume before raycasting in the camera object.  I have an
> old script that did this, but I just tested it out, and it no longer works
> in the current yt paradigm.  I poked around and cannot seem to get it to
> work to do what you want.  Unfortunately, the main point of contact on the
> HomogenizedVolume class is Matt, and he's currently on his honeymoon for a
> few weeks.  Furthermore, I think the path forward in yt was for completely
> doing away with the HomogenizedVolume class in the near future, as it is
> now almost a subclass of functionality of the kdtree.  I think one of the
> main pieces of functionality that was holding up this changeover was that
> which you have discovered--being able to specify data sources to the camera
> object for rendering, as Nathan alluded to above.
> Sam, what is the status of the kdtree being able to handle arbitrary data
> sources for rendering?
>
> For reference, I've attached a modified form of my old script (along with
> some comments for options that wouldn't successfully run) which could do
> this circa 1.5 years ago here: http://paste.yt-project.org/show/3750/
>
> Cameron
>
>
> On Wed, Aug 7, 2013 at 11:57 AM, Munier Azzam Salem <
> msalem at astro.columbia.edu> wrote:
>
>> Thanks Guys,
>>
>>      Kacper, that looks like a work-around for now, thanks.
>>
>>          Munier
>>
>>
>> On Wed, Aug 7, 2013 at 2:53 PM, Kacper Kowalik <xarthisius.kk at gmail.com>wrote:
>>
>>> On 07.08.2013 20:37, Munier Azzam Salem wrote:
>>> > Hey guys,
>>> >
>>> >        I've been trying to make slices of density only looking at
>>> cooler
>>> > gas (i.e. with a cut in Temperature). I've found a nice way to do this
>>> for
>>> > simple projections. But my strategy breaks for Off-Axis projections.
>>> >
>>> > Specifically, this works fine:
>>> > *
>>> > *
>>> > *field_parameters={'field_cuts':["grid['Temperature'] < 1e6 "]})*
>>> > *cold_proj =
>>> > ProjectionPlot(pf,0,'Density',field_parameters=field_parameters)*
>>> > *               *
>>> >
>>> > but this does not:
>>> >
>>> > *cold_proj =
>>> OffAxisProjectionPlot(pf,axis,'Density',north_vector=north,*
>>> > *                                  field_parameters= field_parameters)*
>>> >
>>> > sensibly enough, since field_parameters is not a keyword argument for
>>> off
>>> > axis projections.
>>> >
>>> > Is there a decent workaround for this? Or would this be simple to add
>>> into
>>> > yt's functionality?
>>>
>>> Hi,
>>> I think that you could define auxiliary derived field like
>>>
>>> @derived_field(name = "cut_dens",
>>>    validators = [ValidateSpatial(1)],
>>>    units = r"g/cm^3")
>>> def _cut_dens(field, data):
>>>    cut = data['Density'].copy()
>>>    cut[data['Temperature'] < 1.0e6] = 0.0
>>>    return cut
>>>
>>> and make OffAxisProjection of that.
>>> Cheers,
>>> Kacper
>>>
>>>
>>>
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>>>
>>>
>>
>>
>> --
>> Munier A. Salem // 845.489.6450
>>
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>>
>
>
> --
> Cameron Hummels
> Postdoctoral Researcher
> Steward Observatory
> University of Arizona
> http://chummels.org
>
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