The gridding requires at least Nyquist sampling of the plane to avoid
the artifact known as aliasing. For the signal, the Nyquist sampling in the
plane is obtained with a size of the grid cells equal to half the
size of the antenna diameter (this is the smallest spatial frequency that
the interferometer can be sensitive to, *i.e.* the natural resolution in the
plane). In the image plane, this implies to make an image at least
twice as large as the primary beam size (see Fourier transform property #2
in appendix). Unfortunately, the spatial frequencies of the noise are not
bounded: Noise aliasing can not be avoided, *i.e.* the noise increases at the
edges of the produced image.

Gildas manager 2014-07-01