Content-type: text/html Manpage of convol


Section: User Commands (1)
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convol - Convolve a cube with a "beam function"  




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.  


The input image. This can be two or three dimensional. No default.
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.
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.
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.
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.
The output image. No default.
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.
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.
When doing devonvolution (options=divide), this gives a noise parameter. Default is 0.




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Time: 18:35:38 GMT, July 05, 2011