ring-to-nest confusion

[DanielLenz]

(I've also posted this as a question on stackoverflow, since I'm quite sure that I misunderstood something. Feel free to post there as well and I'll gladly accept the answer.)

I've been working with superpixel masking and ran into something that appeared odd to me. When trying to reproduce the top two panels of Gorski+ (2002, Fig. 4), I did the following:

# This plot shows us the pixels 4, 5, 6, 7 and matches the illustration in the
# Gorski+ (2002) paper, Fig. 4, top two panels

import healpy as hp
import numpy as np
import matplotlib.pyplot as plt

fig, (ax1, ax2, ax3) = plt.subplots(figsize=(14, 14), nrows=3)

nside = 2
npix = hp.nside2npix(nside)

hpkw = dict(min=3, max=8, cmap='jet', rot=[-180, 0], flip='geo', hold=True)

plt.axes(ax1)
hp.cartview(np.arange(npix), title='Input ring ordering', **hpkw)

plt.axes(ax2)
hp.cartview(hp.reorder(np.arange(npix), r2n=True), title='ring-to-nest converted', **hpkw)

plt.axes(ax3)
hp.cartview(hp.reorder(np.arange(npix), n2r=True), title='nest-to-ring converted', **hpkw)
plt.show()

That gives me this figure, which shows that the conversion of the ordering scheme with 'ring2nest' does not work, but 'nest2ring' does, even though the input map is in ring ordering.

What am I missing here?

[zonca]

When you plot NESTED you need to set nest=True

Il ven 27 ott 2017, 20:50 Daniel notifications@github.com ha scritto:

I've been working with superpixel masking and ran into something that appeared odd to me. When trying to reproduce the top two panels of Gorski+ (2002, Fig. 4) http://iopscience.iop.org/article/10.1086/427976/pdf, I did the following:

This plot shows us the pixels 4, 5, 6, 7 and matches the illustration in the

Gorski+ (2002) paper, Fig. 4, top two panels

fig, (ax1, ax2, ax3) = plt.subplots(figsize=(14, 14), nrows=3)

hpkw = dict(min=3, max=8, cmap='jet', rot=[-180, 0], flip='geo', hold=True)

plt.axes(ax1) hp.cartview(np.arange(npix1), title='Input ring ordering', **hpkw)

plt.axes(ax2) hp.cartview(hp.reorder(np.arange(npix1), r2n=True), title='ring-to-nest converted', **hpkw)

plt.axes(ax3) hp.cartview(hp.reorder(np.arange(npix1), n2r=True), title='nest-to-ring converted', **hpkw) plt.show()

That gives me this figure https://github.com/healpy/healpy/files/1423096/ring_nest_conversion.pdf, which shows that the conversion of the ordering scheme with 'ring2nest' does not work, but 'nest2ring' does, even though the input map is in ring ordering.

What am I missing here?

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[DanielLenz]

Thanks for the quick solution!