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    As MAKE_MOSAIC, but supports frequency dependent beams (4-D dirty beams).

    This  task  combines  individual dirty images and beams corresponding to
    various pointing centers into a "mosaic" which is suited for further de-
    convolution using the MAPPING program.

    Mosaics  are  ensemble  of overlapping fields, with typically half power
    primary beam overlap, and similar (but not identical) UV  coverages  for
    each  field. Individual images for every field should be created with  a
    common phase tracking center. The UV_SHIFT, MAP_RA  and   MAP_DEC  vari-
    ables in task UV_MAP must be used for this.  The image names must derive
    from a generic name as follows (e.g. for a generic name  MAP)
         MAP-1.LMV, MAP-2.LMV, ... MAP-N.LMV
    where N is the number of fields.

    For example
    LET MAP_SIZE 256 512
    LET MAP_CELL 0.5
    LET MAP_RA     20:39:10
    LET MAP_DEC    68:01:20
    LET WCOL 1
    FOR I 1 TO 10

    MAKE_MOSAIC produces a combined image (MAP.LMV), a data cube of  primary
    beams  (MAP.LOBE),  a  data cube of dirty beams (MAP.BEAM), and a weight
    image MAP.WEIGHT, which are required for cleaning.

    Two parameters are very important in the mosaic  creation:  the  primary
    beam  width (FWHM), and the truncation threshold of the primary beam. It
    is recommended to use a relatively high value for this threshold, 0.2 to
    0.4, to avoid contaminating adjacent field in case of pointing errors.

Gildas manager 2018-03-19