Though selfcal
can handle multiple pointings and frequency ranges,
it assumes that the antenna gain is independent of feed (i.e. the *X*
and *Y* gains are the same). It also only handles Stokes-I models
(and ignores visibilities that are unrelated to determining Stokes-I).

Task gpscal is intended for telescopes with dual feeds (either linear or circular), such as the ATCA. Indeed, it will fail for other sorts of data.

- gpscal
solves for the two feeds either totally independently, or
with the constraint that the
*XY*(or*RL*) phase of an antenna must be constant with time. - gpscal converts between Stokes parameters and raw polarisations. It can take multiple input models for different Stokes parameters. However, if a model of a particular Stokes parameter is not given, it is assumed to be zero. For example, if you give it models of I, Q and U, but not V, then the source is assumed to have no circular polarisation.
- gpscal uses the antenna polarisation leakage table if this information is present. If it is not present, leakages are assumed to be zero.
- Unlike selfcal, gpscal cannot take models from multiple pointings or from different frequency ranges. All models must correspond to the same pointing and same frequency range.

2016-06-21