Concat

Help on concat task:

Concatenate several visibility data sets.

The list of data sets given in the vis argument are concatenated into an output
data set in concatvis.  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.


Keyword arguments:
vis -- Name of input visibility files to be combined
        default: none; example: vis = 'mydata.ms',
             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'

        other examples: 
           concat(vis=['src2.ms','ngc5921.ms'], concatvis='src2.ms')
               will concatenate 'ngc5921.ms' into 'src2.ms', and the original
               src2.ms is lost

           concat(vis=['src2.ms','ngc5921.ms'], concatvis='out.ms') 
               will concatenate 'ngc5921.ms' and 'src2.ms' into a file named 
               'out.ms'; the original 'ngc5921.ms' and 'src2.ms' are untouched.

           concat(vis=['v1.ms','v2.ms'], concatvis = 'vall.ms')
              then
           concat(vis=['v3.ms','v4.ms'], concatvis = 'vall.ms')
             vall.ms will contains v1.ms+v2.ms+v3.ms+v4.ms

     Note: run flagmanager to save flags in the concatvis


freqtol -- Frequency shift tolerance for considering data to be in the same
           spwid.  The number of channels must also be the same.
        default: ''  do not combine unless frequencies are equal
        example: freqtol='10MHz' will not combine spwid unless they are
           within 10 MHz.
        Note: This option is useful to conbine 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: '' means always combine.
        example: dirtol='1.arcsec' 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.

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.