psimager

Fast dirty imaging of measurement sets for power spectrum analyses: dirty Stokes and PSF images with the ducc0 w-gridder, with the options, file names and FITS keywords of WSClean, so that pspipe and ps_eor read them as WSClean images.

The MSs are read once, in large row chunks, and the output channels are gridded in parallel, each by one ducc0 call. Imaging many channels is then many times faster than with WSClean, which reorders the data on disk and grids one image at a time.

Installation

pip install psimager

Usage

psimager -name img -size 400 400 -scale 6amin -pol IV -channels-out 363 -weight natural \
    -minuv-l 5 -maxuv-l 100 -data-column CORRECTED_DATA -even-odd -make-psf -no-dirty obs*.MS

writes img-even-0000-I-image.fits, img-even-0000-V-image.fits, img-even-0000-psf.fits, ..., for each output channel, for the even and the odd time steps.

Options

As WSClean's: -name, -data-column, -pol, -size, -scale, -channel-range, -channels-out, -interval, -intervals-out, -even-timesteps, -odd-timesteps, -minuv-l, -maxuv-l, -minuvw-m, -maxuvw-m, -weight natural|uniform|briggs ROBUST, -visibility-weighting-mode, -taper-edge, -padding (of the weighting grid), -wgridder-accuracy, -j, -parallel-gridding, -mem, -abs-mem, -make-psf, -no-dirty. See psimager --help.

Differences with WSClean:

• -even-odd images the even and the odd time steps in one pass, as NAME-even-* and NAME-odd-*.
• -fits-keyword KEY=VALUE (repeatable) adds a header keyword to every output file, written with the file instead of updating it afterwards.
• -parallel-gridding defaults to -j: one thread per output channel, which is the fastest.
• No deconvolution and no -MFS- images.
• WSClean's gridding options (-oversampling, -kernel-size, -nwlayers, -grid-mode, -reorder, -temp-dir, ...) are accepted and ignored, with a warning, so that a WSClean command line runs unchanged.
• Only single-field, single-SPW MSs with linear correlations.

The data are read in chunks of at most 30 GB by default (-abs-mem), or -mem % (33) of the node's memory if smaller, so that several psimager runs can share a node, e.g. as job steps of a Slurm allocation; give -abs-mem to use more on a node of its own.

Images are in Jy/PSF (the PSF peaks at 1), one file per output channel and Stokes parameter, with WSClean's WSCNVIS, WSCENVIS, WSCVWSUM, WSCIMGWG and WSCNORMF computed from the Stokes I weights, and BMAJ, BMIN, BPA fitted to the PSF.