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 is used to specify the gaussian beam used when convolving.
Normally it gives the size of the beam to convolve with, but
using options=final causes CONVOL to interpret the parameters
as 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. If only one number is given, the gaussian will have
equal major and minor axes.
This parameter is ignored if the "beam" keyword is given.

Key: pa
The position angle, in degrees, of the gaussian beam.
Normally this is the position angle of the beam that is used
when convolving. However options=final causes this parameter to
be interpreted as the required position angle in the effective
beam of the output image.
It is measured north through towards east, in degrees.
This parameter is ignored if the "beam" keyword is given.

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.

Key: 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.

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