1 UV_SINGLE
        UV_SINGLE

    This task prepares one or more (for mosaics) UV tables of short spacings
    from  a   single-dish  table  of  spectra  (as produced by CLASS command
    GRID).  This table may later be merged to an  interferometer  UV  table.
    Two major steps are performed for this:
      - Creation of a "well behaved" map from the spectra.
      - Extraction of UV spacings from this map.

    The "well behaved" map is obtained by linear  operations  (convolutions)
    from  the original spectra, in an optimum way from signal to noise point
    of view. The map is extrapolated smoothly towards zero at the  map  edge
    in  order  to avoid further aliasing in the Fourier transform operations
    required in step 2. This extrapolation has a scale length of  twice  the
    single-dish beam, in order to avoid spurious Fourier components.

    To obtain it, UV_SINGLE performs the following operations:
      -  Resampling (in space) of the original spectra on a regular grid  by
        convolution  with  a  small  (typically 1/4 of the single-dish beam)
        gaussian  convolving  kernel.  In  this  process,  the  weights   of
        individual spectra is carried on a weight map.
      -  Extrapolation by zero outside the convex hull of the mapped region
      -  Convolution of the result by  a  gaussian  twice  as  wide  as  the
        single-dish beam.
      -  Within the convex hull of the mapped region, the  smoothed  map  is
        replaced by the original map.

    From this map, UV_SINGLE computes one or several UV tables (one for each
    pointing center in case of a mosaic) 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 (SD_DIAM$, in meters)
      -  Inverse Fourier transform to  the  image  plane
    and then for each pointing center
      -   Multiplication  of  the   image   by  the  primary  beam  of   the
        interferometer elements
      -  Fourier transform back to the UV plane.
      -  Creation of the UV table, with a given  weight  SD_WEIGTH$  and  an
        appropriate calibration factor to Janskys SD_FACTOR$

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

2 TABLE$

    The table of spectra produced by CLASS command GRID.

2 MAP$

    The name  of  the  single  dish  map  which  will  be  produced  (as  an
    intermediate result) by UV_SINGLE

2 XCOL$

    The number of column containing X offsets. For tables produced by  CLASS
    command GRID, XCOL$ should be 1.

2 YCOL$

    The number of column containing X offsets. For tables produced by  CLASS
    command GRID, YCOL$ should be 2.

2 WCOL$

    The number of column containing the weights of the spectra.  For  tables
    produced by CLASS command GRID, WCOL$ should be 3.

2 MCOL$

    The first and last column to be mapped. For tables produced  by  command
    CLASS,  MCOL$[1] should be 4 and MCOL$[2] can be set to 0 to process all
    channels.

2 WEIGHTMODE$

    The weighting mode. Use 'NA' for Natural weighting.

2 TOLE$

    The tolerance in position. Spectra differing by less  than  this  amount
    will be added together prior to gridding.

2 MINWEIGHT$

    The minimum weights under which a given  point  in  the  map  should  be
    filled  by  the  smooth  map  rather than by the gridded (original) map.
    Default value of 0.01 and 0 is appropriate.

2 UV_TABLE$

    Generic output UV table name, without  extension.  When  the  number  of
    fields NF$ is larger than 1, UV_SINGLE will add -'I' to the generic name
    to create a UV table for field I.

2 DO_SINGLE$

    Logical value, should be YES except for test purposes.

2 SD_DIAM$

    Useful diameter of the single dish, in meters.  No spacing  higher  than
    SD_DIAM$ is generated.

2 SD_BEAM$

    Half-power beam width of the single dish antenna, in radians.  The  beam
    is assumed to be gaussian.

2 SD_WEIGHT$

    Total weight of the generated visibilities.  If set to 0, it will be set
    to  10**-6/sigma**2,  where  sigma  is  the  r.m.s.  of the zero-spacing
    value (total flux) in janskys.

2 SD_FACTOR$

    Multiplicative calibration factor; it is used to convert from the single
    dish map units (e.g., main-beam brightness temperature) to janskys.

2 DO_PRIMARY$

    Logical value, should be YES except for test purposes.

2 IP_BEAM$

    Half-power beam width of the interferometer antennas, in  radians.   The
    beam is assumed to be gaussian.

2 MOSAIC_RA$

    The Right Ascension (HH:mm:ss.sss) of the center of  the  interferometer
    field  (center  of mosaic or pointing center of the interferometer for a
    single field).

2 MOSAIC_DEC$

    The Declination (Sdd:mm:ss.sss) of  the  center  of  the  interferometer
    field  (center  of mosaic or pointing center of the interferometer for a
    single field).

2 NF$

    Number of fields to be created. NF$ should be equal  to  the  number  of
    fields  used  in the mosaic at the interferometer. NF$ is 1 for a normal
    observation.

2 DRA$

    Projected offsets on the sky of  the  pointing  centers  of  the  mosaic
    fields  parallel to the right ascension axis, with respect to the mosaic
    center defined by MOSAIC_RA$ and MOSAIC_DEC$.

2 DEC$

    Projected offsets on the sky of  the  pointing  centers  of  the  mosaic
    fields  parallel  to  the  declination  axis, with respect to the mosaic
    center defined by MOSAIC_RA$ and MOSAIC_DEC$.

1 END