Documentation 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.

Key: tol
        Interpolation tolerance, in minutes. This gives the maximum
        gap between two integrations to interpolate across. The default is
        2 minutes.