2.2.1.0 calibrater.selectvis

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calibrater.selectvis - Function

2.2.1 Set the data selection for subsequent processing
Description

This function provids for selection of the visibility data from the MS which will be treated by subsequent execution of the solve and correct functions. Note that data selection is not cumulative, i.e., any selection made in a previous call to selectvis will be overridden by the the current call.

Most of the selectvis parameters use the standardized MS Selection syntax.

The parameters are described below. The selected data will satisfy the logical AND of all non-trivially specified parameters. Note that the old-fashioned strided channel selection parameters are deprecated (and will soon be removed); use spw instead. Running selectvis with no specified parameters restores selection of the entire MS.

time: is used to specify time ranges in a stardard format
spw: is used to specify spectral window and channel selection. Currently, only a single channel range can be specified per spw.
scan: is used to specify scan numbers and ranges
field: is used to specify field names or indices
baseline: is used to specify antenna and baseline combinations
uvrange: is used to specify baseline length ranges
chanmode: is deprecated (use spw)
nchan: is deprecated (use spw)
start: is deprecated (use spw)
step: is deprecated (use spw)
mstart: is deprecated (use spw)
mstep: is deprecated (use spw)
msselect: is used to specify a subselection of data according to Measurement Set columns in conditional combinations not possible with the standard parameters above. This parameter should be specified as a valid TaQL expression. If both msselect and the standard selection parameter are used together, they are combined with a logical AND, i.e., the data must jointly satisfy all selectvis parameters.

Arguments


Inputs
time		Select on time
		allowed:	any
		Default:	variant
spw		Select on spectral window
		allowed:	any
		Default:	variant
scan		Select on scan
		allowed:	any
		Default:	variant
field		Select on field
		allowed:	any
		Default:	variant
baseline		Select on antennas/baselines
		allowed:	any
		Default:	variant
uvrange		Select by uvrange
		allowed:	any
		Default:	variant
chanmode		Type of data selection: channel or velocity
		allowed:	string
		Default:	channel velocity none
nchan		Number of channels to select (mode=’channel’)
		allowed:	int
		Default:	1
start		Start channel (0-relative) (mode=’channel’)
		allowed:	int
		Default:	0
step		Step in channel number (mode=’channel’)
		allowed:	int
		Default:	1
mstart	km/s	Start velocity (e.g. ’20Km/s’)
		allowed:	doublekm/s
		Default:	0.0
mstep	km/s	Step in velocity (e.g. ’100m/s’)
		allowed:	doublekm/s
		Default:	0.0
msselect		TAQL selection string. Default (empty) is no specific selection.
		allowed:	string
		Default:

Returns
bool

Example

Open and select a field:

cb.open(’ngc5921.ms’);
cb.selectvis(field=’N5921_2’);  # by complete name
cb.selectvis(field=’N5921*’);   # with wildcard
cb.selectvis(field=’2’);        # by index

Select a field and a channel range:

cb.selectvis(spw=’0:10~40’,field=’N5921*’);

Select using all MS Selection parameters (these parameters are over-specified somewhat, i.e., scan 6 contains only field N5921_2, etc.):

cb.selectvis(time=’>1995/04/13/10:40:00’,   # times greater than this
             spw=’0:20~40’,                 # channels 20-40 in spw 0
             scan=’6’,                      # scan 6 only
             field=’N59*’,                  # fields matching N59*
             baseline=’1 \& *’,              # baselines to antenna 1
             uvrange=’>0.0klambda’)         # baselines greater than zero length

Reset selection to the entire dataset

cb.selectvis()

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