TRANSFORM FFT

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TRANSFORM FFT

            [CALIBRATE\]TRANSFORM FFT  FileIn FileOut [Nchan]

        Compute the Fourier Transform of FileIn along the Frequency/Velocity ax-
        is.  The direction of the Fourier Transform depends  on  the  nature  of
        FileIn.

        If  FileIn  is  a standard Data Cube, a direct Fourier transform is per-
        formed, that leads to 4-D cube  as  FileOut,  in  order  (position,posi-
        tion,complex,velocity).  Its 3rd axis has 2 pixels that contain the Real
        and Imaginary parts.  The number of channels is extended to the  nearest
        integer of the form 2^n 3^p 5^q where p and q are less or equal to 2.

        Conversely,  if  FileIn is such a 4-D cube, an inverse Fourier transform
        is performed, leading to a (position,position,velocity) cube as FileOut.
        Optionally, Nchan can specify how many channels are actually retained in
        this case.