concat – Concatenate several visibility data sets. – utility, manipulation task

Description

The list of data sets given in the vis argument are chronologically concatenated into an output data set in concatvis, i.e. the data sets in vis are first ordered by the time of their earliest integration and then concatenated. If concatvis already exists (e.g., it is the same as the first input data set), then the other input data sets will be appended to the concatvis data set.There is no limit to the number of input data sets.

If there are fields whose direction agrees within the direction will be the one from the chronologically first input MS. Spectral windows for each data set with the same chanelization, and within a specified frequency tolerance of another data set will be combined into one spectral window.

If none of the input data sets have any scratch columns (model and corrected columns), none are created in the concatvis. Otherwise these columns are created on output and initialized to their default value (1 in model column, data in corrected column) for those data with no input columns.

Each appended dataset is assigned a new observation id (provided the entries in the observation table are indeed different).

Parameters

Title

Parameter	Default	Description
vis	numpy.array( [  ] )	Name of input visibility file
concatvis	''	Name of output visibility file
freqtol	''	Frequency shift tolerance for considering data as the same spwid
dirtol	''	Direction shift tolerance for considering data as the same field
respectname	False	If true, fields with a different name are not merged even if their direction agrees
timesort	False	If true, sort by TIME in ascending order
copypointing	True	Copy all rows of the POINTING table.
visweightscale	numpy.array( [  ] )	List of the weight scaling factors to be applied to the individual MSs
forcesingleephemfield	''	Make sure that there is only one joint ephemeris for every field in this list

Parameter Explanations

vis

numpy.array( [  ] )

Name of input visibility file

default: none

Example: vis=’[‘src2.ms’,’ngc5921.ms’,’ngc315.ms’]

concatvis

''

Name of visibility file that will contain the concatenated data

default: none

Example: concatvis=’outvis.ms’

Note: if this file exits on disk then the input files are added to this file. Otherwise the new file contains the concatenated data. Be careful here when concatenating to an existing file.

freqtol

''

Frequency shift tolerance for considering data as the same spwid. The number of channels must also be the same.

Default: ‘’ == 1 Hz

Example: freqtol=’10MHz’ will not combine spwid unless they are within 10 MHz.

Note: This option is useful to combine spectral windows with very slight frequency differences caused by Doppler tracking, for example.

dirtol

''

Direction shift tolerance for considering data as the same field

Default: ‘’ == 1 mas (milliarcsec)

Example: dirtol=’1arcsec’ will not combine data for a field unless their phase center differ by less than 1 arcsec.

Note: If the field names are different in the input data sets, the name in the output data set will be the first relevant data set in the list.

respectname

False

If true, fields with a different name are not merged even if their direction agrees (within dirtol)

Default: False

timesort

False

If true, sort by TIME in ascending order

Default: False (data in order as read in)

Example: timesort=True

Note: There is no constraint on data that is simultaneously observed for more than one field; for example multi-source correlation of VLBA data.

copypointing

True

Make a proper copy of the POINTING subtable

Default:True (can be time consuming!)

If False, the result is an empty POINTING table.

visweightscale

numpy.array( [  ] )

List of the weight scaling factors to be applied to the individual MSs

Default: [] (empty list) - no scaling

The weights of the individual MSs will be scaled in the concatenated output MS by the factors in this list. SIGMA will be scaled by 1/sqrt(factor). Useful for handling heterogeneous arrays. Use plotms to inspect the “Wt” column as a reference for determining the scaling factors.

Example: [1.,3.,3.] - scale the weights of the second and third MS by a factor 3 and the SIGMA column of these MS by a factor 1/sqrt(3).

forcesingleephemfield

''

Make sure that there is only one joint ephemeris for every field in this list

Default: ‘’ (standard treatment of all ephemeris fields)

By default, concat will only merge two ephemeris fields if the first ephemeris covers the time range of the second. Otherwise, two separate fields with separate ephemerides are placed in the output MS. In order to override this behaviour and make concat merge the non-overlapping or only partially overlapping input ephemerides, the name or id of the field in question needs to be placed into the list in parameter ‘forcesingleephemfield’.

Example: [‘Neptune’] - will make sure that there is only one joint ephemeris for field Neptune in the output MS