uniqpix

Summary:

This file contains a summary of which uniqpix are covered by this survey and program.

Naming Convention:

uniqpix-SURVEY-PROGRAM.fits, where SURVEY is main, sv1, sv2, sv3, special, or cmx; and PROGRAM is bright, dark, backup, or other.

Regex:

uniqpix-(cmx|main|special|sv1|sv2|sv3)-(backup|bright|dark|other).fits

File Type:

FITS, 430 KB

Contents

Number	EXTNAME	Type	Contents
HDU0		IMAGE	Blank
HDU1	UNIQPIX	BINTABLE	Table with UNIQPIX, NTARGETS, NSPECTRA

FITS Header Units

HDU0

This HDU has no non-standard required keywords.

Empty HDU.

HDU1

EXTNAME = UNIQPIX

Table giving the number of targets and spectra for each uniqpix in this survey and program.

Required Header Keywords

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	24	int	Size of each table row
NAXIS2	17929	int	Number of table rows = number of uniqpix
SURVEY	main	str	DESI survey name, e.g. main, sv1, sv2, sv3, special, or cmx
PROGRAM	dark	str	DESI program name, e.g. bright, dark, backup, or other
SPECPROD	matterhorn	str	DESI spectro pipeline product name, e.g. matterhorn or nevis

Required Data Table Columns

Name	Type	Units	Description
UNIQPIX	int64		Unique pixel identifier = healpix + 4*nside^2
NTARGETS	int64		Number of unique TARGETIDs in this uniqpix for this survey and program
NSPECTRA	int64		Number of input uncoadded spectra in this uniqpix for this survey and program

Notes and Examples

Example usage:

from astropy.table import Table
import numpy as np
import healpy

survey = 'special'
program = 'dark'
upix_table = Table.read(f'spectra/{survey}/{program}/uniqpix-{survey}-{program}.fits')
for upix, ntargets in upix_table['UNIQPIX', 'NTARGETS']:
    nside = 2**int(np.log2(upix//4)/2)
    hpix = upix - 4 * nside**2
    area = healpy.nside2pixarea(nside, degrees=True)
    density = ntargets / area

    pixgroup = upix//100
    coaddfile = f'spectra/special/dark/{pixgroup}/{upix}/coadd-special-dark-{upix}.fits'

    print(f'{coaddfile} at {nside=} has {ntargets} targets ({density:,.1f}/deg^2)')

Output for the matterhorn production:

spectra/special/dark/0/5/coadd-special-dark-5.fits at nside=1 has 353 targets (0.1/deg^2)
spectra/special/dark/0/7/coadd-special-dark-7.fits at nside=1 has 3965 targets (1.2/deg^2)
spectra/special/dark/0/9/coadd-special-dark-9.fits at nside=1 has 1147 targets (0.3/deg^2)
...
spectra/special/dark/6996/699669/coadd-special-dark-699669.fits at nside=256 has 2119 targets (40,395.9/deg^2)
spectra/special/dark/6996/699670/coadd-special-dark-699670.fits at nside=256 has 2045 targets (38,985.2/deg^2)
spectra/special/dark/6996/699671/coadd-special-dark-699671.fits at nside=256 has 1261 targets (24,039.3/deg^2)

Note that the vastly different target densities are covered by different nside pixels so that each file has at most a few thousand targets.