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 there are fields whose direction agrees within the direction tolerance (parameter dirtol), the actual direction in the resulting, merged output field will be the one from the chronologically first input MS.

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 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.

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.

A field position in one data set that is within a specified direction tolerance of another field position in any other data set will be combined into one field. The field names need not be the same—only their position is used.

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

Keyword arguments: vis – Name of input visibility files to be combined

default: none; example: vis = [‘src2.ms’,’ngc5921.ms’,’ngc315.ms’]

concatvis – Name of visibility file that will contain the concatenated data

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.

default: none; example: concatvis=’src2.ms’

example: concatvis=’outvis.ms’

freqtol – Frequency shift tolerance for considering data to be in 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. 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 – If true, fields with a different name are not merged even if their

direction agrees (within dirtol) default: False

timesort – If true, the output visibility table will be sorted in time.

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 – Make a proper copy of the POINTING subtable (can be time consuming).

If False, the result is an empty POINTING table. default: True

visweightscale – 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. See the cookbook for more details. 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).

default: [] (empty list) - no scaling

forcesingleephemfield – 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

default: ‘’ - standard treatment of all ephemeris fields

Parameters

Title

Parameter	Default	Description
vis	numpy.array( [  ] )
concatvis	''
freqtol	''
dirtol	''
respectname	False
timesort	False
copypointing	True
visweightscale	numpy.array( [  ] )
forcesingleephemfield	''

Parameter Explanations

vis

numpy.array( [  ] )

Name of input visibility files to be concatenated

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