Basic Information on uvdiff

Task: uvdiff
Purpose: Difference two visibility datasets.
Categories: uv analysis

        Given two Miriad visibility datasets, UVDIFF matches and
        optionally subtracts one from the other.  In doing this, UVDIFF
        assumes that the two datasets sample the same source using the
        same array configuration and observing frequency setup (no
        checks are made to verify these).  UVDIFF matches visibility
        records based on baseline number, polarisation type and hour
        angle.  If the hour angles in the two datasets do not match to
        better than 1 second, UVDIFF linearly interpolates between two
        integrations of one dataset to the appropriate hour angle of the
        other.
 
        NOTE: UVDIFF does not apply calibration corrections to either
        of the input datasets.  The datasets should be in time order.

Key: vis
        The two datasets to difference.  No default.  When differencing,
        the output is the first minus the second.  The first visibility
        dataset is used as the template for the output.  It is the
        second dataset that is interpolated when needed.

Key: select
        Standard visibility selection keyword.  See the help on select
        for more information.  Note that this selection is applied ONLY
        to the first visibility dataset.  The default is to select
        everything.

Key: out
        The output dataset.  No default.

Key: mode
        This determines what data is written.  Possible values are:
          difference Write the difference of the two inputs (the first
                     minus the second).  This is the default.
          two        Write the data from the second input, interpolated
                     to the first.
          one        Write the first dataset.
        With the exception of the visibility data itself, all three
        possibilities will produce identical datasets.  This includes
        identical flagging information.
        Any of these modes can be prefixed with a minus sign.  In this
        case the output visibilities are negated.

Key: tol
        Interpolation tolerance, in minutes.  This gives the maximum gap
        between two integrations to interpolate across.  The default is
        2 minutes.
 
Revision: 1.10, 2021/06/02 04:45:09 UTC