change_polcconv


This IDL facility changes the coordinate convention in FITS file containing a polarised sky map. The main effect is to change the sign of the U Stokes parameter, and add/update the POLCCONV FITS header with either COSMO or IAU value.

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


FORMAT

IDL> CHANGE_POLCCONV , File_In, File_Out[, /I2C, /C2I, /C2C, /I2I, /FORCE]


QUALIFIERS

File_In
name of a FITS file to be read

File_Out
name of a FITS file to be written, after modification of the polarisation coordinate convention, if applicable


KEYWORDS

/I2C
changes from IAU to COSMO coordinate convention
-if POLCCONV is not found or found with value 'IAU', it is added/replaced with value 'COSMO', and the sign of the U stokes parameter map is changed
-if POLCCONV already has value 'COSMO', File_In is copied unchanged into File_Out

/C2I
changes from COSMO to IAU coordinate convention
-if POLCCONV is not found or found with value 'COSMO', it is added/replaced with value 'IAU', and the sign of the U stokes parameter map is changed
-if POLCCONV already has value 'IAU', File_In is copied unchanged into File_Out

/C2C
does NOT change coordinate system
-if POLCCONV is found with value 'IAU', program will issue error message and no file is written
-in all other case POLCCONV is set/added with value 'COSMO', but data is NOT changed

/I2I
does NOT change coordinate system
-if POLCCONV is found with value 'COSMO', program will issue error message and no file is written
-in all other case POLCCONV is set/added with value 'IAU', but data is NOT changed

/FORCE
if set, the value of POLCCONV read from the FITS header is ignored. The sign of U is swapped (if used with /C2I or /I2C), and the FITS keyword is updated accordingly.


DESCRIPTION

This routine will change the sign of the U Stokes parameters (and related quantities, such as the TU and QU cross-correlations) and update the 'POLCCONV' FITS keyword where applicable. The recognised format are:
- standard Healpix full sky polarised format
- cut sky Healpix polarised format
- WMAP 2nd year polarised format


RELATED ROUTINES

This section lists the routines related to change_polcconv

idl
version 6.4 or more is necessary to run change_polcconv
write_fits_cut4
This HEALPix IDL facility can be used to write a (polarised or unpolarised) cut sky map into a FITS file.
read_fits_cut4
This HEALPix IDL facility can be used to read a (polarised or unpolarised) cut sky map from a FITS file.
write_tqu
This HEALPix IDL facility can be used to write a polarised full sky map (with either the standard Healpix format or the WMAP 2nd year format) into a FITS file
read_tqu
This HEALPix IDL facility can be used to read a polarised cut sky map from a FITS file


EXAMPLE:

change_polcconv, 'map_cosmo.fits','map_iau.fits',/c2i
Modify the file 'map_cosmo.fits', which was using the 'COSMO' convention for polarisation coordinate convention into 'map_iau.fits' which uses the 'IAU' convention

Version 3.31, 2017-01-06