[ Basic Info | User Guide ]

# Basic Information on 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: 1.11, 2017/04/10 05:36:06 UTC
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Generated by miriad@atnf.csiro.au on 10 Apr 2017