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Sort My Fields [public]

Which of my telescope fields contain the greatest probability of containing the counterpart? The code below reads in a list of fields and a skymap, samples the skymap for the probability at each field center, and sorts into a list with decreasing probability.

# Rank a list of (right ascension, declination) points according to descending
# probability density. See attached file for example input.

import os
import healpy as hp
import numpy as np

# Download list of RA, Dec points.
os.system('curl -O')
# Download example sky map.

# Read RA, Dec list.
fields = np.recfromtxt('CRTS_fields2.txt', names='name,ra,dec')

# Read sky map.
skymap = hp.read_map('bayestar.fits.gz', verbose=False)

# Determine HEALPix resolution.
nside = hp.npix2nside(len(skymap))
deg2perpix = hp.nside2pixarea(nside, degrees=True)

# Convert from RA, Dec in degrees to spherical polar coordinates.
theta = 0.5 * np.pi - np.deg2rad(fields['dec'])
phi = np.deg2rad(fields['ra'])

# Interpolate sky map at each point.
# Note that the sky maps are deliberately over-sampled, so alternatively you
# could just evaluate the probability at the nearest neighbor of each point,
# like this:
# prob = skymap[hp.ang2pix(theta, phi)]
prob = hp.get_interp_val(skymap, theta, phi)

# Rank points by descending posterior probability density.
prob_fields = sorted(zip(prob, fields), reverse=True)

# Print top 20 fields.
print('Field      RA        Dec    Prob. / deg^2')
for p, field in prob_fields[:20]:
    print('{0:s}  {1:8.4f}  {2:8.4f}  {3:.4f}'.format(
        field['name'], field['ra'], field['dec'], p / deg2perpix))

-- RoyWilliams - 21 Apr 2015
Topic attachments
I Attachment Action Size Date Who Comment
CRTS_fields2.txttxt CRTS_fields2.txt manage 145 K 2015-04-22 - 03:05 UnknownUser A list of fields as "name RA Dec"
Topic revision: r7 - 2018-05-29, adminuser
Warning: Can't find topic LV_EM.WebLeftBarExample

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