NRAO Home > CASA > CASA Toolkit Reference Manual
calibrater.selectvis - Function

2.1.1 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
observation
is used to specify observation ID(s).
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

intent

Select on intent or state

allowed:

any

Default:

variant

observation

Select by observation ID(s)

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()  
 
 

__________________________________________________________________


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

Copyright 2016 Associated Universities Inc., Washington, D.C.

This code is available under the terms of the GNU General Public Lincense


Home | Contact Us | Directories | Site Map | Help | Privacy Policy | Search