In [rgb]1,0,0IMAGER, the variants of the CLEAN algorithms discussed above are
coded as the following commands: magentaHOGBOM, magentaCLARK, magentaMX,
magentaSDI, magentaMULTI and magentaMRC. All those commands work on two
internal buffers containing the dirty beam and dirty image. Both buffers
are created directly from uv table through the magentaUV_MAP command, or
they can be loaded from files through the magentaREAD BEAM and
magentaREAD DIRTY commands. The behavior of those commands is controlled
through the following common red SIC variables:
- Iterative search
-
- blueCLEAN_POSITIVE
- Number of positive clean components to be found
before enabling the search for negative components. Default is 0.
- blueCLEAN_GAIN
- Loop gain. Default is 0.2, good compromise between
stability and speed.
- Stopping criteria
-
- blueCLEAN_STOP
- Compact way to specify the stopping criterium. Defaut
is currently empty, but might be set to magenta2 SIGMA as a good general default.
- blueCLEAN_NITER
- Maximum number of clean components. Default is 0.
- blueCLEAN_FRES
- Maximum amplitude of the absolute value of the
residual image. This maximum is expressed as a fraction of the peak
intensity of the dirty image. Default value is 0.
- blueCLEAN_ARES
- Maximum amplitude of the absolute value of the
residual image. This maximum is expressed in the image units (Jy/Beam).
Default value is 0.
- blueCLEAN_NKEEP
- Minimum number of Clean components be-
fore testing if Cleaning has converged. Default value is 70.
- Support
-
- blueBLC and blueTRC
- Bottom Left Corner and Top Right
Corner of a square support in pixel units. Default is 0, which means
using only the inner quarter if no other support is defined.
- magentaSUPPORT
- A command that defines the support where
to search for clean components. The support can be a Mask, or a
Polygon. For a Polygon, the definition can be interactive,
using the red GREG cursor. This definition can be stored in a file
through the magentaWRITE SUPPORT command and read back in memory from
the file with the magentaSUPPORT command. The polygon support definition is
stored in the blueSUPPORT% structure. Command magentaSUPPORT /MASK
instructs [rgb]1,0,0IMAGER to use the Mask instead of the polygon for the
Clean support.
- magentaMASK
- Command magentaMASK is used to define a Mask-like
support. This can be interactive, or automatic using a thresholding
technique in command magentaMASK THRESHOLD. The computed Mask
can be saved by command magentaWRITE MASK. The Mask can also be
read by command magentaREAD MASK. Command magentaMASK USE is
equivalent to command magentaSUPPORT /MASK, and instructs
[rgb]1,0,0IMAGER to use the Mask instead of the polygon for the Clean
support.
- Clean beam parameters
-
- blueBEAM_SIZE
- is a 3-element array that gives the FWHM size of the major
and minor axes (in arcsec) and position angle (in degree) of the
Gaussian used to restore the clean image from the clean component list.
Default is all parameters at 0, meaning use the fit of the main lobe of
the dirty image. Changing the default value of those parameters is
dangerous. The beam size effectively used is available in blueBEAM_FITTED.
Other variables control specific aspects of a subclass of the CLEAN
algorithm:
- blueCLEAN_NCYCLE
- Maximum number of major cycles in all algorithms
using this notion (magentaCLARK, magentaMX, magentaSDI). Default is 50.
- blueBEAM_PATCH
- Size (in pixel units) of the dirty beam used to
deconvolve the residual image in minor cycles. It is used in magentaCLARK and
magentaMRC algorithms only. Default value is 0. This is for development only.
- blueCLEAN_SMOOTH
- Smoothing factor between different scales in
the MULTISCALE methods. Default value is sqrt(3).
- blueCLEAN_RATIO
- Smoothing factor between different scales in
the MRC method. Default value is 0, for which the code automatically
derives the best power of 2 adequate for the current problem.
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Up: Implementation and typical use
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Gildas manager
2023-06-01