It has member functions to retrieve the fields commonly needed in synthesis calibration and imaging. It is derived from the read-only iterator ROVisibilityIterator . One should use VisBuffer to access chunks of data. This class provides that access. This will flag all channels in the original data that contributed to the output channel in the case of channel averaging.
All polarizations have the same flag value.
This is possibly only for a 'reference' MS which has a new DATA column. If the MS does not contain all polarizations, only the parallel hand polarizations are used.