smoothing

This program can be used to convolve a map with a gaussian beam. The input map can be given in RING or NESTED scheme and the smoothed map is written to a FITS file in the RING scheme.
NOTE: This automated facility is susceptible to problems with non-commutativity of discrete spherical harmonics transforms, described in the Recommendations for Users of the anafast facility. If very high accuracy of the results is required in the spectral regime of $\ell > 2\cdot nsmax$, it is recommended to choose an iterative computation of the $a_{\ell m}$ coefficients.

Location in HEALPix directory tree: src/f90/smoothing/smoothing.f90 

FORMAT

% smoothing [options] [parameter_file]

COMMAND LINE OPTIONS

-d

--double

double precision mode (see Notes on double/single precision modes)

-s

--single

single precision mode (default)

QUALIFIERS

simul_type =

Defines which map(s) to analyse, 1=temperature only, 2=temperature AND polarisation. (default= 1)

infile =

Defines the filename for the FITS file containing the map to be smoothed. (default= 'map.fits')

nlmax =

Defines the $\ell_{\mathrm{max}}$ value for the application. (default= 64)

iter_order =

Defines the maximum order of quadrature iteration to be used. (default=0, no iteration). For details, see the map2alm_iterative routine described in the ”Fortran Subroutines” document.

fwhm_arcmin =

Defines the FWHM in arcminutes of the gaussian beam for the convolution. (default=10)

beam_file =

Defines the FITS file describing the Legendre window function of the circular beam to be used for the simulation (see ”Beam window function files” in introduction). If set to an existing file name, it will override the fhwm_arcmin given above. default=`'

outfile =

Defines the filename for the file that will contain the smoothed map. (default='map_smoothed.fits')

plmfile =

Defines the name for an input file containing precomputed Legendre polynomials $P_{\ell m}$. (default= no entry — smoothing executes the recursive evaluation of $P_{\ell m}$s)

w8file =

Defines name for an input file containing ring weights in the improved quadrature mode (default= no entry — the name is assumed to be 'weight_ring_n0xxxx.fits' where xxxx is nsmax)

w8filedir =

Gives the directory where the weight files are to be found (default= no entry — smoothing searches in the default directories, see ”Default file names and directories” in introduction)

won =

Set this to 1 if ring-based quadrature weight files are to be used, or to 2 to use pixel-based weight files instead; otherwise set it to 0. (default= 0)

DESCRIPTION

A FITS file containing a HEALPix map in RING or NESTED scheme is read in. When dealing with polarized signal maps, the smoothing behavior will depend on the value of the POLCCONV FITS keyword (see note on POLCCONV in The HEALPix Primer). The map is analysed and smoothed in fourier space with a gaussian beam of a given FHWM. A new map is then synthesized using the smoothed $a_{\ell m}$ coefficients. For a more accurate application, an iteration of arbitrary order can be applied. The output map is stored in the same scheme as the input map.

DATASETS

The following datasets are involved in the smoothing processing.

Dataset	Description
data/weight_ring_n0xxxx.fits	Files containing ring weights for the smoothing improved quadrature mode.

SUPPORT

This section lists those routines and facilities (including those external to the HEALPix distribution) which can assist in the utilisation of smoothing.

generate_beam

This HEALPix Fortran subroutine generates or reads the $B(\ell)$ window function used in smoothing

map2gif

This HEALPix Fortran facility can be used to visualise the input and output maps of smoothing.

mollview

This HEALPix IDL facility can be used to visualise the input and output maps of smoothing.

synfast

This HEALPix facility can generate a map and also do the smoothing.

anafast

This HEALPix facility can analyse a smoothed map.

EXAMPLE # 1:

smoothing

Smoothing runs in interactive mode, self-explanatory.

EXAMPLE # 2:

smoothing filename

When `filename' is present, smoothing enters the non-interactive mode and parses its inputs from the file `filename'. This has the following structure: the first entry is a qualifier which announces to the parser which input immediately follows. If this input is omitted in the input file, the parser assumes the default value. If the equality sign is omitted, then the parser ignores the entry. In this way comments may also be included in the file. In this example, the file contains the following qualifiers:
simul_type= 1
nlmax= 64
infile= map.fits
outfile= map_smoothed.fits
fwhm_arcmin= 10.
iter_order= 1
smoothes the HEALPix temperature map contained in `map.fits' with a 10 arcmin FWHM beam. The resulting map is saved in `map_smoothed.fits'. The map analysis/synthesis was carried out using fourier coeffecients up to an $\ell$ value of 64. A first order iteration of the quadrature was performed.

RELEASE NOTES

■ Initial release (HEALPix 0.90)

■ Extension to polarization and arbitrary circular beams (HEALPix 1.20)

■ Support for pixel-based quadrature weights when won=2 (HEALPix 3.40)

MESSAGES

This section describes error messages generated by smoothing

Message	Severity	Text
can not allocate memory for array xxx	Fatal	You do not have sufficient system resources to run this facility at the map resolution you required. Try a lower map resolution.