UV_SHORT Step_2

          Step (2) Extraction of UV visibilities from this map.

    From the given input data cube, or the "well behaved" data cube  created  by
    Step (1), UV_SHORT  computes the visibilities in the following way:

      - Fourier transform of the single dish map;
      - Division by  the Fourier  transform of  the single dish  beam, up  to a
        maximum spacing (SHORT_SD_DIAM, in meters);
      - Inverse Fourier transform to the image plane and then for each pointing
        center;
        - Multiplication of the  image by the primary beam  of the interferomete
          elements;
        - Fourier transform back to the UV plane;
        - Creation  of the  visibilities,  with  a given  weight  SHORT_SD_WEIGH
          and an appropriate calibration factor to Janskys SHORT_SD_FACTOR.

    Both  the  single-dish and the  interferometer antennas are assumed  to have
    gaussian beams (SHORT_SD_BEAM and SHORT_IP_BEAM, in radians).