SHTs not working for resampled maps

[ajvanengelen]

• pixell version: 0.16.0
• Python version: 3.8
• Operating System: Linux

Description

Taking an SHT of a higher-res map that was upsampled from a lower-res map is throwing an error. The difference is apparently the crval value in the WCS, being different from what it is if I just make the higher-res map from the start.

What I Did

from pixell import enmap, curvedsky
import numpy as np

#Check that we can take an SHT of a full-sky map at 5-arcmin resolution
small_resolution_arcmin = 5.
shape_small, wcs_small = enmap.fullsky_geometry(res = small_resolution_arcmin / 60 * np.pi / 180.)
mymap_small = enmap.ndmap( (np.zeros(shape_small)), wcs_small)
#This SHT works fine:
mysht_small = curvedsky.map2alm(mymap_small, lmax = 3000)

#Now start with a low-res map, then upsample it to the shape of the high-res map, and try the SHT
big_resolution_arcmin = 60
shape_big, wcs_big =  enmap.fullsky_geometry(res = big_resolution_arcmin / 60 * np.pi / 180.)
mymap_big = enmap.ndmap( (np.zeros(shape_big)), wcs_big)
mymap_resampled = enmap.resample(mymap_big, oshape = shape_small, method = 'spline')
#This SHT throws an error:
mysht_resampled = curvedsky.map2alm(mymap_resampled, lmax = 3000)

Here is the error report:

Here is the difference in WCS values:

[ajvanengelen]

Am I supposed to get the ainfo in some other way for this map which apparently has slightly different pixel positions?