Basic Information on convol

Task: convol
Purpose: Convolve a cube with a "beam function"
Categories: map manipulation, map analysis

        CONVOL is a MIRIAD task which convolves a map or model with a
        "beam".  WARNING: Convol does not do a very good job with masked
        images.
 

Key: map
        The input image. This can be two or three dimensional.
        No default.

Key: beam
        The input beam.  This cannot be 3-dimensional.  The beam is
        generally assumed to be symmetrical about its reference pixel,
        but see the "asymmetric" option if this is not so.  If this is
        not given, then a Gaussian beam must be specified by the fwhm
        and pa parameters.

Key: fwhm
        This parameter is ignored if the "beam" keyword is given.
        Otherwise, it specifies the width of the Gaussian convolving
        function unless options=final, in which case it specifies the
        required resolution of the output image.  The size, in arcsec,
        will normally be two numbers giving the full-width at half-
        maximum of the major and minor axes of the Gaussian.  At least
        one number must be given.  If only one is given, the Gaussian
        will have equal axes.

Key: pa
        This parameter is ignored if the "beam" keyword is given.
        Otherwise, it specifies the position angle of the Gaussian
        convolving function, unless options=final, in which case it
        specifies the required position angle of the effective beam of
        the output image.  It is measured north through towards east, in
        degrees.  Default 0.

Key: region
        The region of the input map to convolve.  See the Users Manual
        for instructions on how to specify this.  The default is the
        entire input image.

Key: out
        The output image. No default.

Key: options
        Some extra processing options. Several can be given, separated
        by commas. Minimum match is used.
          "final"    When parameters are given by the FWHM and PA
                     keywords, the "final" option causes CONVOL to
                     interpret these as the resolution required for the
                     final output image.
          "divide"   Divide, rather than multiply, the transform of the
                     map by the transform of the beam.  That is, perform
                     deconvolution, rather than convolution.
          "asymmetric" Normally the beam is assumed to be symmetric (as
                     it normally is in radio astronomy).  This options
                     causes CONVOL to go through the extra steps to
                     handle a possibly asymmetric beam.  If the beam is
                     asymmetric, and you do not give this option, CONVOL
                     symmetrises the beam (i.e. discards the anti-
                     symmetric component).
          "correlate" Correlate rather than convolve with the beam.  The
                     difference between correlation and convolution are
                     only apparent for asymmetric beams.
          "cube"     Like final, but calculate required convolution for
                     each plane separately. This option implies final.
                     Use this to get the same beamsize in arcsec in all
                     planes rather than the same beamsize in pixels.
                     Warning: analysis tasks are likely to get source
                     size and total flux wrong for the resulting cube.
      @ scale
        The scale factor to multiply the output by.  The default is for
        CONVOL to determine the appropriate scale factor to make the
        output in JY/BEAM.
        NOTE: If the input image is in units of JY/BEAM, then to
        determine the appropriate scale factor, CONVOL must know the
        beam parameters (bmaj, bmin and bpa items) of both the input map
        and the beam.  If these items are not present, CONVOL issues a
        warning and uses a scale factor of 1.

Key: sigma
        When doing devonvolution (options=divide), this gives a noise
        parameter. Default is 0.
 
Revision: 1.13, 2018/12/05 23:26:16 UTC