[yt-users] questions on projection

[Geoffrey So]

Hi, I just tried your script on a small enzo dataset of 64 cube in size

"
1. What exactly is returned in proj2? Why does it span from 0. to 1. when I
specified source=cube?"

- proj2['Density'] got values of a 2D matrix showing the results of the
unweighted projection of 'Density' along z in the x,y plane, in my case the
projection was 2x2 pixels.  I think the reason it span from 0 to 1 is
because you ran a simulation with normalized code units the left edge being
0 and right edge being 1.

"2. I also tried 'data_source=cube' instead of 'source=cube'. It did not
raise any error, and returned
something different: array of same shape, but with different data values.
Is this keyword also used
 for projection object? Is there a consistent difference between the two
keywords in yt?"

- I tried
>pf.h.proj(2, 'Density', center=center, data_source=cube)
and got:
KeyError: 'No field named px'

I'm not familiar with the different versions of yt so if you can reply with
the results of
>yt instinfo
I'm sure someone more knowledgable can pinpoint the version you're using
and come up with why there's a discrepancy (I'm using an slightly outdated
developer's version).  I could be wrong so someone please correct me, but
if I recall correctly I think the data_source newer form for specifying the
input in the newer ProjectionPlot API.

"3. I could not find documentation on some fields like 'px', 'py' that seem
to be generated for certain data containers
(e.g., 't' for ray objects). Is there an exhaustive list of such fields in
the documentation?"

- You might have gotten different px, py because you were able to do a
different data_source, if you left it with source=cube, what I got in
return for >proj2['px'] and >proj2['py'], were
 the x y edges of cells that are in the projection proj2 in the normalized
code units.

- doing a
>help(proj2)
revealed that proj2 is an 'AMRProj' object, putting it into the search in
the documentation revealed the API page for that base object at the
following link
http://yt-project.org/doc/api/generated/yt.data_objects.data_containers.AMRProjBase.html?highlight=amrproj
from there I only see 'source' as a kwarg and not data_source, so that's
probably why I'm getting an error when I tried it.

- doing a
>proj2.fields
lists the different fields, some like x, dx are in cgs, and px and pdx are
in your simulation code units, in this case normalized to 1.  I believe the
x, dx are the cell-center, and cell-center-distance.  I'm not sure about
px, pdx, but looking at the values (I changed halfwidth=0.05 to have a
bigger than 2x2 projection to play with), I'm going to guess px is the
distance of each cell to the center of the projection parallel to x, and
pdx is the x-spacing between each cell center.

Hope this helps.

From
G.S.

PS. The documentation is being actively improved upon by the developers, so
I believe feedback are always welcomed.



On Mon, Aug 19, 2013 at 9:22 PM, Semyeong Oh <semyeongoh at gmail.com> wrote:

> Hi all,
>
> I'm new to yt. I have questions about making projections of certain
> region, and inspecting the data returned.
>
> I made a cube as follows:
>
> import pylab as pl
>
> center = [0.5, 0.5, 0.5]
> halfwidth = 0.005
> cube = pf.h.region(center, center-pl.ones(3)*halfwidth,
> center+pl.ones(3)*halfwidth, ['Density'])
>
> print min(cube['x']), max(cube['x'])
> 0.494873046875 0.505126953125
>
> When I print cube['x'].shape, I get (10728,).
> I tried to make a projection of this cube along z-axis as follows:
>
> proj2 = pf.h.proj(2, 'Density', center=center, source=cube)
>
> But I could not understand what is returned.
>
> print min(proj2['p
> x']), max(proj2['py']), proj2['px'].shape
> 0.00390625 0.99609375 (19648,)
>
> print proj2['Density']
> [ 0.  0.  0. ...,  0.  0.  0.]
>
> My questions are:
> 1. What exactly is returned in proj2? Why does it span from 0. to 1. when
> I specified source=cube?
>
> 2. I also tried 'data_source=cube' instead of 'source=cube'. It did not
> raise any error, and returned
> something different: array of same shape, but with different data values.
> Is this keyword also used
> for projection object? Is there a consistent difference between the two
> keywords in yt?
>
> 3. I could not find documentation on some fields like 'px', 'py' that seem
> to be generated for certain data containers
> (e.g., 't' for ray objects). Is there an exhaustive list of such fields in
> the documentation?
>
> Thanks in advance.
>
> Semyeong
>
> _______________________________________________
> yt-users mailing list
> yt-users at lists.spacepope.org
> http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
>
>
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