AIPS NRAO AIPS HELP file for CCMOD in 31DEC21



As of Sat Oct 23 20:09:22 2021


CCMOD: Task to generate clean components from a model source

INPUTS

INNAME                             Image name (name)
INCLASS                            Image name (class)
INSEQ             0.0    9999.0    Image name (seq. #)
INDISK            0.0       9.0    Disk drive #
INVERS           -1.0   46655.0    CC file ver. no.: 0 higest
                                      -1 new version
OPCODE                             Model type: 'DISK','GAUS',
                                      'DISG'
FLUX                               Model flux
BMAJ              0.0              Model major axis in pixels
BMIN              0.               Model minor axis in pixels
BPA            -360.0     360.0    Position angle of major axis
GWIDTH                             DISG: Gaussian bmaj,bmin,bpa
PIXXY          -100.0    8192.0    Model center in pixels
BITER                              Place results after comp #
                                   0 -> max, <0 -> at start

HELP SECTION

CCMOD
Type:  Task
Use:   CCMOD generates a set of Clean components for a model source.
       These components are then inserted into the Clean components file
       (CC) associated with an image.  This task is useful for
       generating clean components of an extended source of known
       parameters a priori.  Further Cleaning (APCLN, IMAGR, etc) can
       then be done.
Adverbs:
  INNAME......The image name (name).    Standard defaults.
  INCLASS.....The image name (class).   Standard defaults.
  INSEQ.......The image name (seq. #).  0 => highest.
  INDISK......The disk drive #.         0 => any.
  INVERS......The CC file ver #.        0 => highest current one.
              -1 => create new one.  If none exists, one will be created
              in any case.  Be careful with this.  If you request some
              large number you will get it.
  OPCODE......The model type: 'DISK' or 'GAUS' or 'POIN' or 'DISG'
                 The last is a disk multiplied by a Gaussian.
  FLUX........The total flux density in the model
  BMAJ........The model major axis in asec. Diameter for 'DISK',
              FWHP for 'GAUS' in pixels
  BMIN........The model minor axis in pixels.
  BPA.........The position angle (deg) of the major axis.
  GWIDTH......FWHM of major axis of Gaussian in DISG, FWHM of minor axis,
              position angle.
  PIXXY.......(X,Y,...) position of center of the model in pixels.
              PIXXY(3 - 7) not used.
  BITER.......Place model components after component BITER.  Note that
              components BITER+1 through BITER+n get replaced by the
              model, where n is the number of cells with significant
              value.  Set BITER = 0 or large to write at the end of the
              current CC file, retaining all current components.  Set
              BITER < 0 to start at the beginning replacing all current
              components.

EXPLAIN SECTION

CCMOD:  Task to generate Clean components from a model source.
DOCUMENTOR:  Alan Bridle (NRAO-Charlottesville)
RELATED PROGRAMS:  APCLN, PHCLN, PRTCC

                          PURPOSE

     As described in the documentation of APCLN, Clean algorithms
attempt to answer the question "What is the distribution of amplitudes
at the Clean component positions which best fits the visibility data, if
we define the sky to be blank everywhere else ?"  Clean can then be
thought of a "search" for places where there should be components, and
an adjustment of the intensities at these places to obtain the best
agreement with the data.

     The user can greatly assist the search for appropriate locations
for Clean components by telling Clean where the source is and what shape
it should be.  Specifying the "Clean Window" via NBOXES and BOX in APCLN
gives the algorithm a boundary within which to hunt for emission, but
still allows it to find components one at a time within this boundary by
searching the residual map.  This can (and does) lead to a scattering of
Clean components through an extended region, with empty areas between
them - a "pincushion" of components where an extended emission region
may be more plausible.  This is inefficient if the user KNOWS that the
source being mapped should have emission EVERYWHERE within a certain
boundary, i.e. that EVERY LOCATION within that boundary should have a
Clean component whose amplitude is to be adjusted.

     CCMOD provides a means of telling IMAGR that this is the case, by
generating an initial list of Clean components from a specified model
rather than by searching a map one location at a time.  Three types of
model are provided - DISKs, GAUSsians and their product, selected by the
OPCODE parameter.  DISK is intended for use when mapping planets, the
Sun, or other objects in which fine detail is superposed on a bright
filled disk background.  GAUS may find applications to sources where a
right diffuse region fades at the edges, e.g. lobes of extragalactic
sources.

     FLUX is the total flux density in the model.  BMAJ and BMIN are in
units of pixels.  The model is first computed and then the component
scaling is determined so that the flux in the model matches the FLUX
adverb.

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