Documentation on offaxis

Task: offaxis
Purpose: Remove (or simulate) ATCA off-axis instrumental polarisation.
Categories: uv analysis

        OFFAXIS is a Miriad task which attempts to remove off-axis
        instrumental polarisation from ATCA observations. As input,
        OFFAXIS takes a visibility dataset and a model of the source
        total intensity (Stokes I). Given this, it computes the expected
        off-axis effects (given its internal models of the effects),
        subtracts this from the data, and produces an output (nominally)
        corrected dataset.

        Currently this only handle 13-cm off-axis effects!!

Key: vis
        Input visibility dataset. No default.

Key: select
        Normal visibility selection parameter. The default is to
        select all data. See the help on select for more information.

Key: line
        Normal line parameter with the normal defaults. See the help on
        line for more information.

Key: model
        Input model of the total intensity image. No default. This should
        be the apparent total intensity (i.e. not corrected for primary
        beam attenuation).

Key: out
        The name of the output, corrected, visibility dataset. No default.

Key: clip
        Pixels in the model less (in absolute value) than the clip level
        are treated as if they are 0. The default is 0.

Key: options
        Task enrichment parameters. Several can be given, separated by
        commas. Only the minimum number of characters to guarantee
        uniqueness are needed. Possible options are:
          replace   Normally OFFAXIS subtracts the computed off-axis
                    response from the data. This option causes the
                    visibility to be replaced with the model.
          nocal     Do not apply any antenna gain calibration. The default
                    is to apply these if they are available.
          nopol     Do not apply any polarization leakage correction. The
                    default is to apply these if they are available.
          nopass    Do not apply bandpass calibration. The default is to
                    apply these calibrations if they are available.