The list of data sets given in the vis argument are concatenated into an output data set in testconcatvis without the bulk data of the MAIN table. This is useful for obtaining the information in the merged subtables without actually performing a time-consuming concatenation of the MAIN tables on disk.

Keyword arguments:
vis -- Name of input visibility files for which the subtables are to be combined
default: none; example: vis = '',
testconcatvis -- Name of MS that will contain the concatenated subtables
default: none; example: testconcatvis=''

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.

copypointing -- Make a proper copy of the POINTING subtable (can be time consuming).
If False, the result is an empty POINTING table.
default: True