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What imager needs:

imager operates on a specified MeasurementSet to produce any of a range of different types of image: dirty, point spread function, clean, residual, etc. A MeasurementSet is the holder for measurements from a telescope. It is simply an AIPS++ Table obeying certain conventions as to required and optional contents. The intention is that it should contain all the information needed to reduce synthesis and single dish observations (see AIPS++ Note 191). A UVFITS file can be converted to a MeasurementSet using the fitstoms tool function (a constructor of the ms tool.

imager adds some extra columns to the MeasurementSet to store results of processing. The following columns in the MS are particularly important:

DATA

The original observed visibilities are in a column called DATA. These are not altered by any processing in AIPS++.

CORRECTED_DATA

During a calibration process, as carried out by e.g. calibrater, the visibilities may be corrected for calibration effects. This corrected visibilities are stored in a column CORRECTED_DATA which is created on demand by calibrater and imager. In creating the CORRECTED_DATA column, imager will only correct for parallactic angle rotation. This can be controlled using the correct tool function. All imaging performed by imager is from the CORRECTED_DATA column (apart from the tool function makeimage which can also make dirty images from the other visibility columns).

MODEL_DATA

During various phases of processing, the visibilities as predicted from some model are required. These model visibilities are stored in a column MODEL_DATA. These are used by the calibrater tool for calibration.

IMAGING_WEIGHT

Weighting of data (including natural, uniform and Briggs weighting, and tapering) is accomplished by setting the column IMAGING_WEIGHT appropriately.

Standard tools such as the table module and the ms can be used to access and possibly change these (and all other) columns.

imager can handle an initial model in a number of forms: as an image, as a list of images, as a componentmodels:componentlist, or as some combination. Fitting of componentmodels is planned but is not currently supported.

imager uses a number of scratch files. Following AIPS++ practice, these are placed in the directories specified in the aipsrc variable user.directories.work. Those disks that possess sufficient free disk space are chosen in sequence. So to spread your scratch files over two disks each of which has a directory tcornwel/tmp do e.g.

user.directories.work:   /bigdisk1/tcornwel/tmp /bigdisk2/tcornwel/tmp