[yt-dev] Issue #570: Healpix volume rendering produces garbled, artifacted images (yt_analysis/yt)

[Geoffrey So]

I can confirm, the images I got looks like the grids were not ordered
correctly, patches of zones looks fine inbetween, but zone and zones do not
match well at the boundary.

From
G.S.


On Fri, May 17, 2013 at 1:49 PM, Nathan Goldbaum <issues-reply at bitbucket.org
> wrote:

> New issue 570: Healpix volume rendering produces garbled, artifacted images
>
> https://bitbucket.org/yt_analysis/yt/issue/570/healpix-volume-rendering-produces-garbled
>
> Nathan Goldbaum:
>
> Using the sample script from the docs:
>
>
> ```
> #!python
>
> from yt.mods import *
> import yt.visualization.volume_rendering.camera as camera
>
> pf = load("IsolatedGalaxy/galaxy0030/galaxy0030")
> image = camera.allsky_projection(pf, [0.5,0.5,0.5], 100.0/pf['kpc'], 64,
> "Density")
> camera.plot_allsky_healpix(image, 64, "allsky.png", "Column Density
> [g/cm^2]")
> ```
>
> Produces the following image:
>
> ![](http://i.imgur.com/5wskzay.png)
>
> I also tried the manual method described further down in the docs:
>
>
> ```
> #!python
>
> rom yt.mods import *
> import yt.visualization.volume_rendering.camera as camera
>
> Nside = 32
> pf = load("IsolatedGalaxy/galaxy0030/galaxy0030")
> cam = camera.HEALpixCamera([0.5,0.5,0.5], 0.2, Nside, pf = pf, log_fields
> = [False])
> bitmap = cam.snapshot()
>
> import yt.utilities.lib as au
> from numpy import pi
> phi, theta = np.mgrid[0.0:2*pi:800j, 0:pi:800j]
> pixi = au.arr_ang2pix_nest(Nside, theta.ravel(), phi.ravel())
> img = np.log10(bitmap[:,0,0][pixi]).reshape((800,800))
>
> import matplotlib.figure
> import matplotlib.backends.backend_agg
>
> fig = matplotlib.figure.Figure((10, 5))
> ax = fig.add_subplot(1,1,1,projection='mollweide')
> image = ax.imshow(img, extent=(-pi,pi,-pi/2,pi/2), clip_on=False,
> aspect=0.5)
> cb = fig.colorbar(image, orientation='horizontal')
>
>
> cb.set_label(r"$\mathrm{Column}\/\mathrm{Density}\/[\mathrm{g}/\mathrm{cm}^2]$")
> canvas = matplotlib.backends.backend_agg.FigureCanvasAgg(fig)
> canvas.print_figure("allsky.png")
>
> ```
> Note that I had to update this a bit since amr_utils was renamed a while
> back.  This produces the following image:
>
> ![](http://i.imgur.com/Jax1sYB.png)
>
> While this looks more sensible, it's not clear to me that it is correct.
>
>
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>
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