Phase self-calibration

Image reconstruction based on the Fourier transform of the complex visibilities requires the visibility phases in addition to the amplitudes. Since phase information is only available as closure phases, phase self-calibration is used with an initial model to minimize the differences between model closure phases and observed phases by adjusting telescope-based phase offsets (which caused by the atmosphere). The procedure set_complexvis performs this operation using a point-source model and must be called before the use of pearl. Within the latter, the phase self-calibration is performed with the current image by selfcal (button SELFCAL).