Managing flag versions (flagmanager)

The flagmanager task will allow you to manage different versions of flags in your data. These are stored inside a CASA flag versions table, under the name of the MS .flagversions. For example, for the MS jupiter6cm.usecase.ms, there will need to be jupiter6cm.usecase.ms.flagversions on disk. This is created on import (by importasdm, importevla, importvla or importuvfits) or when flagging is first done on an MS without a .flagversions (e.g. with plotxy).

By default, when the .flagversions is created, this directory will contain a flags.Original table containing a copy of the original flags in the MAIN table of the MS so that you have a backup. It will also contain a file called FLAG_VERSION_LIST that has the information on the various flag versions there. The flag versions are cumulative, i.e. a specific version number contains all the flags from the lower version numbers, too.

The flags are stored in an MS column of the same spectral and correlator polarization shape as the visibility data values, with Boolean 1 to indicate that a particular time, channel, polarization has been flagged or 0 for unflagged.

The inputs for flagmanager are:

The mode=’list’ option will list the available flag versions from the .flagversions file in the logger. For example:

The mode parameter expands the options. For example, if you wish to save the current flagging state of vis=:

with the output version name specified by versionname. For example, the above xyflags version was written using:

and you can see that there is now a sub-table in the flag versions directory:

It is recommended that you use this task regularly to save versions during flagging.

Note that if a flag version already exists under a name, the task will give a warning and add a suffix ’.old.timestamp’ to the previous version.

You can restore a previously saved set of flags using the mode=’restore’ option:

The merge sub-parameter will control how the flags are restored. For merge=’replace’, the flags in versionname will replace those in the MAIN table of the MS. For merge=’and’, only data that is flagged in BOTH the current MAIN table and in versionname will be flagged. For merge=’or’, data flagged in EITHER the MAIN or in versionname will be flagged.

The mode=’delete’ option can be used to remove versionname from the flag versions: