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ms.split - Function

1.3.1 make a new ms from a subset of an existing ms, adjusting subtables and indices


Description

This function splits out part of the MS into a new MS. Time and channel averaging can be performed in the process (but not in the same call).

When splitting multiple spectral windows, the parameters nchan, start, step can be vectors, so that each spectral window has its own selection on averaging and number of output channels. But the option of using only one value for each of these parameters means that it will be replicated for all the spectral windows selected.

Arguments





Inputs

outputms

The name of the resulting measurement set

allowed:

string

Default:

field

Fields to include, by names or 0-based ids. (” => all)

allowed:

variant

Default:

spw

Spectral windows (and :channels) to select

allowed:

variant

Default:

*

step

number of input per output channels - Int vector of length 1 or same as spw

allowed:

intArray

Default:

1

baseline

Antenna names or indices to select (” => all)

allowed:

variant

Default:

timebin

Duration for averaging. Defaults to no averaging.

allowed:

variant

Default:

-1s

time

Only use data in the given time range, using the msselection syntax.

allowed:

string

Default:

scan

Only use the scan numbers requested using the msselection syntax.

allowed:

variant

Default:

uvrange

Limit data by uv distance using the msselection syntax.

allowed:

variant

Default:

taql

For the TAQL experts, flexible data selection using the TAQL syntax

allowed:

string

Default:

whichcol

’DATA’, ’MODEL_DATA’, ’CORRECTED_DATA’, ’FLOAT_DATA’, ’LAG_DATA’, and/or ’all’

allowed:

string

Default:

DATA

tileshape

Tile shape of the disk data columns, most users should not need to touch this parameter [0] => normal tiling, [1] => fast mosaic style tile [4,15,351] => a tile shape of 4 pol 15 chan and 351 rows

allowed:

variant

Default:

subarray

Limit data to specific (sub)array numbers.

allowed:

variant

Default:

combine

Ignore changes in these columns (scan, and/or state) when time averaging.

allowed:

string

Default:

correlation

Limit data to specific correlations (LL, XX, LR, XY, etc.).

allowed:

string

Default:

intent

Only use the requested scan intents.

allowed:

string

Default:

obs

Only use the requested observation IDs.

allowed:

string

Default:

Returns
bool

Example

 
 
  ms.open("multiwin.ms")  
  ms.split(’subms.ms’, field=[0], spw=[0], nchan=[10],  
           start=[0], step=[5], whichcol=’CORRECTED_DATA’)  
 
  In this example we split out data from the 1st field and 1st  
  spectral window. The output data will have 10 channels which is  
  taken from 50 channels from the input data starting at channel 0 and  
  averaging every 5.  
 
 
  ms.open("multiwin.ms")  
  ms.split(’subms.ms’, field=[0], spw=[0,1,2,3], nchan=[10],  
           start=[0], step=[5], whichcol=’CORRECTED_DATA’)  
 
In this example we split out data from the 1st field and four spectral  
windows. The output data will have 4 spectral windows each of 10  
channels which is taken from 50 channels from the input data starting  
at channel 0 and averaging every 5.  
 
 
  ms.open("multiwin.ms")  
  ms.split(’subms.ms’, field=[0], spw=[0,1,2,3], nchan=[10,10,30,40],  
           start=[0,4,9,9], step=[1,10,5,2], whichcol=’CORRECTED_DATA’)  
 
In this example we split out data from the 1st field and four spectral  
windows. There will be four spectral windows in the output data,  
with 10, 10, 30 and 40 channels respectively. These are averages  
of the input spectral windows. The first output spectral window  
will be formed by picking 10 channels, starting at 0 with no  
averaging, of the input spwid 0. The second output spectral window  
will consists of 10 channels and is formed by picking 100 channels  
from spwid 1 of the input data, starting at channel 4, and every  
10 channels to make one output channel.  
 
 
  ms.open("WSRT.ms")  
  ms.split(’subms.ms’, timebin=’20s’, whichcol=’all’, combine=’scan’)  
  ms.close()  
 
  This example averages a WSRT MS into 20s bins, selecting whichever of DATA,  
  MODEL_DATA, CORRECTED_DATA, or FLOAT_DATA, or LAG_DATA is present.  Normally  
  the bins would not cross scans, but in this MS the scan number goes up with  
  each integration, making it redundant enough with time that it would defeat  
  any time averaging.  Therefore the combine parameter forces the SCAN column  
  to be ignored for setting the bins.  
 

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