13.1.2 Fast Fourier Transform

In practice, everybody uses the Fast Fourier Transform because of its definite speed advantage. The drawback of the methods is the need to regrid the visibilities (which are measured at arbitrary points in the (u,v) plane) on a regular grid to be able to perform a 2-D FFT. This gridding process will introduce some distortion in the dirty image and dirty beams, which should be corrected afterwards. Moreover, the gridded visibilities are sampled on a finite ensemble. As discussed in more details below, this sampling introduces aliasing of the dirty image (and beam) in the map plane.