read_tqu

This IDL facility reads a temperature+polarization Healpix map (T,Q,U) from a binary table FITS file, with optionally the error (dT,dQ,dU) and correlation (dQU, dTU, dTQ) from separate extensions

Location in HEALPix directory tree: src/idl/fits/read_tqu.pro 

FORMAT

IDL> READ_TQU , File, TQU, [Extension=, Hdr=, Xhdr=, /HELP, Nside=, Ordering=, Coordsys=]

QUALIFIERS

File

name of a FITS file from which the maps are to be read

TQU

: array of Healpix maps of size ( N_pix,3,n_ext) where N_pix is the total number of Healpix pixels on the sky, and n_ext $\le$ 3 is the number of extensions read
Three maps are available in each extension of the FITS file :
-the temperature+polarization Stokes parameters maps (T,Q,U) in extension 0
-the error maps (dT,dQ,dU) in extension 1 (if applicable)
-the correlation maps (dQU, dTU, dTQ) in extension 2 (if applicable)

Extension=

(optional),
extension unit to be read from FITS file: either its 0-based ID number (ie, 0 for first extension after primary array) or the case-insensitive value of its EXTNAME keyword. If absent, all available extensions are read.

Hdr=

(optional),
string variable containing on output the contents of the primary header. (If already present, FITS reserved keywords will be automatically updated).

Xhdr=

(optional),
string variable containing on output the contents of the extension header. If several extensions are read, then the extension headers are returned appended into one string array.

Nside=

(optional),
returns on output the HEALPix resolution parameter, as read from the FITS header. Set to -1 if not found

Ordering=

(optional),
returns on output the pixel ordering, as read from the FITS header. Either 'RING' or 'NESTED' or ' ' (if not found).

Coordsys=

(optional),
returns on output the astrophysical coordinate system used, as read from FITS header (value of keywords COORDSYS or SKYCOORD)

KEYWORDS

/HELP

if set, an extensive help is displayed and no file is read

DESCRIPTION

read_tqu reads out Stokes parameters (T,Q,U) maps for the whole sky into a FITS file. It is also possible to read the error per pixel for each map and the correlation between fields, as subsequent extensions of the same FITS file (see qualifiers above). Therefore the file may have up to three extensions with three maps in each. Extensions can be written together or one by one (in their physical order) using the Extension option.
For more information on the FITS file format supported in HEALPix, including the one implemented in read_tqu , see https://healpix.sourceforge.io/data/examples/healpix_fits_specs.pdf.

RELATED ROUTINES

This section lists the routines related to read_tqu

idl

version 6.4 or more is necessary to run read_tqu

synfast

This HEALPix f90 facility can be used to generate temperature+polarization maps that can be read with read_tqu

write_tqu

This HEALPix IDL facility can be used to write out temperature+polarization that can be read by read_tqu.

read_fits_cut4, read_fits_partial, read_fits_map

read_tqu, read_fits_s

HEALPix IDL routines to read cut-sky maps and partial maps, full-sky maps, polarized full-sky maps and arbitrary data sets from FITS files

read_fits_s

This general purpose HEALPix IDL facility can be used to read into an IDL structure maps contained in binary table FITS files.

sxpar

This IDL routine (included in HEALPix package) can be used to extract FITS keywords from the header(s) HDR or XHDR read with read_tqu.

EXAMPLE:

read_tqu, 'map_polarization.fits', TQU, xhdr=xhdr

Reads into TQU the polarization maps contained in the FITS file 'map_polarization.fits'. The variable xhdr will contain the extension(s) header.