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Implementation

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.


next up previous contents index
Next: Restoring step: magentaUV_RESTORE Up: Implementation and typical use Previous: Implementation and typical use   Contents   Index
Gildas manager 2023-06-01