National Radio
Astronomy Observatory

2.3.4.1 The antenna Parameter

The antenna selection string is a semi-colon (’;’) separated list of baseline specifications. A baseline specification is of the form:

• ’ANT1’ — Select all baselines including the antenna(s) specified by the selector ANT1.
• ’ANT1&’ — Select only baselines between the antennas specified by the selector ANT1.
• ’ANT1&ANT2’ — Select only the cross-correlation baselines between the antennas specified by selector ANT1 and antennas specified by selector ANT2. Thus ’ANT1&’ is an abbreviation for ’ANT1&ANT1’.
• ’ANT1&&ANT2’ — Select only auto-correlation and cross-correlation baselines between antennas specified by the selectors ANT1 and ANT2. Note that this is what the default antenna=’’ gives you.
• ’ANT1&&&’ — Select only autocorrelations specified by the selector ANT1.

The selectors ANT1 and ANT2 are comma-separated lists of antenna integer-IDs or literal antenna names, patterns, or regular expressions. The ANT strings are parsed and converted to a list of antenna integer-IDs or IDs of antennas whose name match the given names/pattern/regular expression. Baselines corresponding to all combinations of the elements in lists on either side of ampersand are selected.

Integer IDs can be specified as single values or a range of integers. When items of the list are parsed as literal strings or regular expressions or patterns (see § 2.3.1 for more details on strings). All antenna names that match the given string (exact match)/regular expression/pattern are selected.

ALERT: Just for antenna selection, a user supplied integer (or integer list) is converted to a string and matched against the antenna name. If that fails, the normal logic of using an integer as an integer and matching it with antenna index is done. Note that currently there is no method for specifying a pure index (e.g. a number that will not first be checked against the name).

The comma is used only as a separator for the list of antenna specifications. The list of baselines specifications is a semi-colon separated list, e.g.

will select baselines between antennas 1,2,3 and 4,5,6 (’1&4’, ’1&5’, …, ’3&6’) plus baseline ’10&11’.

The wildcard operator (’*’) will be the most often used pattern. To make it easy to use, the wildcard (and only this operator) can be used without enclosing it in quotes. For example, the selection

will match all antenna names which have ’VA’ as the first 2 characters in the name (irrespective of what follows after these characters).

There is also a negation operator “!” that can be used to de-select antennas or baselines.

Some examples:

Antenna numbers as names: Needless to say, naming antennas such that the names can also be parsed as a valid token of the syntax is a bad idea. Nevertheless, antenna names that contain any of the reserved characters and/or can be parsed as integers or integer ranges can still be used by enclosing the antenna names in double quotes (’ "ANT" ’). E.g. the string

will expand into an antenna ID list 10,11,12,13,14,15,21,22 (assuming the index of the antenna named ’VA22’ is 22). If, however, the antenna with ID index 50 is named ’21’, then the string

will expand into an antenna ID list of 10,11,12,13,14,15,50,22. Keep in mind that numbers are FIRST matched against names, and only against indices if that matching fails. There is currently no way to force a selection to use the index, and if there an antenna with that name it will select that.

Read elsewhere (e.g. info regex under Unix) for details of regular expression and patterns.

Antenna stations Instead of antenna names, the antenna station names are also accepted by the selection syntax., e.g. ’N15’ for the JVLA.

ANT@STATION sections syntax Sometimes, data from multiple array configurations are stored in a single MS. But some antennas may have been moved during reconfiguration and the ’ANT@STATION’ syntax can distinguish between them. ’ANT’ is the antenna name or index and ’STATION’ is the antenna station name, e.g., ’EA12@W03’ selects antenna EA012 but only at times when it is positioned on station W03. Wildcards are accepted, e.g. ’EA12@*’ selects all visibilities from antenna EA12, and ’*@W03’ would select all antennas that are located on station ’W03’ during any observations included in the MS.

More information about CASA may be found at the CASA web page

Copyright © 2010 Associated Universities Inc., Washington, D.C.

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