makecube

Introduction

The makecube program merges multiple images into a cube. This is intended to take individual image planes (as were produced by the old CPimager spectral-line imaging program) and merge them into a cube. The CPimager has been replaced by simager, but this utility is kept for now.

Important notes:

  • All source images must have the same dimensions and coordinate systems.
  • A rest frequency can be provided.
  • Restoring beam (i.e. the image info) is copied from a single specified image. Unfortunately casa images don’t appear to support a restoring beam that varies with frequency.
  • A record of the beam sizes of the input images can be created for future reference.

Running the program

It can be run with the following command, where “config.in” is a file containing the configuration parameters described in the next section.

$ makecube -c config.in

The makecube program is not parallel/distributed, it runs in a single process.

Configuration Parameters

The key parameters to be provided are the output cube name, and the pattern describing the input files. Since makecube could potentially be processing thousands of input files, the input can be described using a pattern like “residual.i.[0..15].restored”. This would result in images residual.i.0.restored to residual.i.15.restored (inclusive) being used to form the cube.

It is possible to specify a rest frequency to be applied to the output cube (since cimager will not provide this). A common value for this, that of the fine-structure line of neutral hydrogen (HI), or 1420405751.786 Hz, can be requested by setting the rest frequency to “HI” in the parameter set. If no rest frequency is provided, or a negative value is given, no rest frequency will be written to the cube.

The image info (which essentially means the beam information) for the output cube is copied from a designated input image. This is, by default, the middle image of the range (specifically, (number of images) / 2, with integer division), but this can be changed by setting beamReference to ‘first’, ‘last’, or a number in the range. The individual beam sizes for each of the input images (assuming they are defined) can be written to an ascii text file for future reference. The file has columns: channel number | major axis [arcsec] | minor axis [arcsec] | position angle [deg]

Here is an example of the start of a beam log:

#Channel BMAJ[arcsec] BMIN[arcsec] BPA[deg]
0 65.7623 36.4139 -54.7139
1 65.7981 36.4222 -54.7605
2 65.8365 36.4324 -54.7985
3 65.8733 36.4413 -54.845
4 65.9082 36.4512 -54.8919

The following table describes the possible parameters.

Parameter Type Default Explanation
Makecube.outputCube string “” Name of the spectral cube to be created.
Makecube.inputNamePattern string “” The pattern describing the input names. See text for details.
Makecube.restFrequency string or float -1.0 The rest frequency to be written to the cube’s coordinate system. Negative values mean nothing is written. Provide either a numerical value or the string “HI” (which is equivalent to 1420405751.786).
Makecube.beamReference string or int mid Which of the input images to get the beam information from. Options include: ‘mid’ (middle image of list), ‘first’, ‘last’, or a number indicating the image (list is zero-based).
Makecube.beamLog string “” Name of the ascii text file to which the beam information for every input file is written.

The following demonstrates a parameter set for a continuum cube (no rest frequency):

Makecube.inputNamePattern     = image.i.cube.clean_ch[0..151].restored
Makecube.outputCube           = image.i.cube.clean.restored
Makecube.restFrequency        = -1.0
Makecube.beamReference        = mid
Makecube.beamLog              = beamFile.image.i.cube.clean.restored.dat

and the following demonstrates a parameter set for a small spectral-line cube focussed on HI emisison:

Makecube.inputNamePattern      = image.i.SLtute.cube_ch[0..31].restored
Makecube.outputCube            = image.i.SLtute.cube.restored
Makecube.restFrequency         = HI
Makecube.beamReference         = mid
Makecube.beamFile              = beamFile.image.i.SLtute.cube.restored.dat