randoms-seed-interations

Summary:

The larger DESI random catalogs (randomsall) contain a single binary table covering the entire Legacy Surveys footprint. They contain meta information (the number of observations, the depth, etc.) derived from pixels in Legacy Surveys CCDs at random RA/Dec coordinates. The content of these files resembles the standard, smaller DESI random catalogs.

Naming Convention:

randomsall-seed-iterations.fits, where seed represents the random seed used to generate the catalog and iterations lists the iteration numbers of the smaller random catalogs that have been concatenated to make the larger random catalog.

Regex:

randoms(-[0-9.]+)?-[0-9]+-[0-9]+\.fits

File Type:

FITS, 63 GB

Contents

Number	EXTNAME	Type	Contents
HDU0		IMAGE	Empty
HDU1	RANDOMS	BINTABLE	Random catalog table

FITS Header Units

HDU0

This HDU has no non-standard required keywords.

Empty HDU.

HDU1

EXTNAME = RANDOMS

Random catalog table

Required Header Keywords

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	68	int	Width of table in bytes
NAXIS2	1124357626	int	Number of rows in table
FILENSID	2	int	HEALPix nside covered by file
FILENEST	T	bool	HEALPix nested (not ring) ordering
FILEHPX	11,5,4	str	HEALPix pixel(s) covered by file
DR	9	int	Legacy Surveys (LS) Data Release used to generate randoms
DENSITY	45000	int	Number of random points generated per sq. deg.
APRAD	0.75	float	Aperture radius used to calculate flux-related quantities (arcsec)
SEED	1	int	Seed used to generate random catalog
ADDMTL	F	bool	True if MTL-related columns were added to this larger random catalog
HPXNSIDE	64	int	HEALPix nside
HPXNEST	T	bool	HEALPix nested (not ring) ordering
SUPP	F	bool	True if randoms were generated by avoiding Gaia sources rather than using LS pixels
RESOLVE	T	bool	True if from unique imaging
RESEED	626	int	Seed used to re-shuffle combined random catalogs to ensure randomness
MTLSPLIT	T	bool	True if MTL-related columns were added to individual, smaller random catalogs

Required Data Table Columns

Name	Type	Units	Description
RA	float64	deg	Right ascension at pixel location
DEC	float64	deg	Declination at pixel location
NOBS_G	int16		Number of images at pixel location in LS g
NOBS_R	int16		Number of images at pixel location in LS r
NOBS_Z	int16		Number of images at pixel location in LS z
PSFDEPTH_G	float32		PSF-based depth at pixel location in LS g
PSFDEPTH_R	float32		PSF-based depth at pixel location in LS r
PSFDEPTH_Z	float32		PSF-based depth at pixel location in LS z
GALDEPTH_G	float32		Galaxy model-based depth at pixel location in LS g
GALDEPTH_R	float32		Galaxy model-based depth at pixel location in LS r
GALDEPTH_Z	float32		Galaxy model-based depth at pixel location in LS z
PSFDEPTH_W1	float32		PSF-based depth in WISE W1 (AB mag system)
PSFDEPTH_W2	float32		PSF-based depth in WISE W2 (AB mag system)
PSFSIZE_G	float32	arcsec	Weighted average PSF FWHM in LS g
PSFSIZE_R	float32	arcsec	Weighted average PSF FWHM in LS r
PSFSIZE_Z	float32	arcsec	Weighted average PSF FWHM in LS z
MASKBITS	int16		Bit mask of possible problems with pixel
EBV	float32		Galactic extinction E(B-V) reddening at pixel from SFD98

Notes and Examples

See http://legacysurvey.org for more details about the corresponding columns for sources extracted by the Tractor in the Legacy Surveys, e.g. the units of the depth quantities.