========================
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
~~~~~~~~~~~~~~~~~~~~~~~~

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ======== ============= ===== ========================================
    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
~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. rst-class:: 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.

.. _`SFD98`: http://adsabs.harvard.edu/abs/1998ApJ...500..525S
.. _`Legacy Surveys`: http://legacysurvey.org
.. _`LS`: http://legacysurvey.org/dr9/catalogs/