The msselect Parameter

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2.3.4.6 The msselect Parameter

More complicated selections within the MS structure are possible using the Table Query Language (TaQL). This is accessed through the msselect parameter.

Note that the TaQL syntax does not follow the rules given in § 2.3.1 for our other selection strings. TaQL is explained in more detail in Aips++ NOTE 199 — Table Query Language (http://aips2.nrao.edu/docs/notes/199/199.html). This will eventually become a CASA document. The specific columns of the MS are given in the most recent MS specification document: Aips++ NOTE 229 — MeasurementSet definition version 2.0 (http://aips2.nrao.edu/docs/notes/229/229.html). This documentation will eventually be updated to the CASA document system.

Most selection can be carried out using the other selection parameters. However, these are merely shortcuts to the underlying TaQL selection. For example, field and spectral window selection can be done using msselect rather than through field or spw:

  msselect=’FIELD_ID == 0’                   # Field id 0 only
  msselect=’FIELD_ID <= 1’                   # Field id 0 and 1
  msselect=’FIELD_ID IN [1,2]’               # Field id 1 and 2
  msselect=’FIELD_ID==0 && DATA_DESC_ID==3’  # Field id 0 in spw id 3 only

ALERT: The msselect style parameters will be phased out of the tasks. TaQL selection will still be available in the Toolkit.

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