[yt-users] Density/Column density along a ray

[Thomas Robitaille]

Thanks everyone for your replies - this is all very helpful!

Thomas

On 8 August 2012 18:14, Matthew Turk <matthewturk at gmail.com> wrote:
> Hi Britton,
>
> I think the easiest way to get out physical distance would be to do:
>
> distance = ((end_point - start_point)**2.0).sum()**0.5
> distance *= pf['cm']  # or whatever unit you want
> ray['dts'] * distance
>
> should give the distance traveled inside each cell.
>
> On Wed, Aug 8, 2012 at 12:09 PM, Britton Smith <brittonsmith at gmail.com> wrote:
>> Hi Thomas,
>>
>> In addition to ray['t'], which will give you the cumulative distance
>> traveled at that point in the ray, you can use ray['dts'] to get the just
>> the distance through each individual cell.  Both of these will be normalized
>> to the total distance of the ray, but you can use ray['dx'] to get you the
>> cell size for each cell intersected by the ray, which you can then use along
>> with 'dts' to calculate the physical distance the ray travels through each
>> cell.
>>
>> Britton
>>
>>
>> On Wed, Aug 8, 2012 at 12:03 PM, j s oishi <jsoishi at gmail.com> wrote:
>>>
>>> Hi Thomas,
>>>
>>> Try doing something like
>>>
>>> ray = pf.h.ray(start_point,end_point)
>>>
>>> density = ray['Density']
>>> t = ray['t']
>>>
>>> where t is the distance along the ray of each sample. It will, by
>>> default, sample at the highest available resolution. If you need
>>> subsampling/interpolation, you'll have to wait for someone more
>>> knowledgeable that I am to jump in.
>>>
>>> j
>>> On Wed, Aug 8, 2012 at 8:56 AM, Thomas Robitaille
>>> <thomas.robitaille at gmail.com> wrote:
>>> > Hi
>>> >
>>> > I'm still relatively new to yt, and I'm trying to figure out a way to
>>> > extract the density along a ray joining two points. I've managed to
>>> > make a plot using PlotCollection.add_ray, but I can't figure out how
>>> > to get the actual data as a Numpy array. Also, I'd ultimately like to
>>> > compute the cumulative column density along the ray, so I'd like to
>>> > ensure that the sampling of distances along the ray is very fine to
>>> > get an accurate column density. Is there a way to do this?
>>> >
>>> > Thanks for any help!
>>> >
>>> > Cheers,
>>> > Tom
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