Basic Information on imsad

Task: imsad
Purpose: image search and destroy
Categories: image analysis

        IMSAD fits a Gaussian to the image histogram to determine the
        true image rms noise, then searches for islands of pixels above
        some cutoff, and attempts to fit Gaussian components to the
        islands.  The fitting is borrowed from the miriad imfit task and
        the island detection from the AIPS SAD task.
 
        Pixels above the clip level are marked in yellow.  Then a square
        region centred on each island is coloured in.
 
        When fitting Gaussians, a cross is plotted at the midpoint of
        the island.  Each island is displayed separately in the top
        left of the display as it is fit.  The centroid of the fit is
        plotted.
 
        Information about the fit for each island is given.
 

Key: in
 
        The name of the input image data set.

Key: region
 
        The region of interest within the image (rectangular only).

Key: range
        Image intensity range to display.  Default is min to max for the
        current plane being displayed.

Key: clip
        Clip  level.  For input images of intensity, any pixels below
        the clip level are excluded from the fitting process.  For other
        sorts of images (e.g. Stokes Q, U or V) pixels whose absolute
        values are below the clip level are excluded from the fit.
 
        The clip level can be specified as a multiple of the true image
        rms (using the hist option) or as an absolute pixel value.  No
        default.

Key: box
        The minimum extents for island boundaries.  This would usually
        be some multiple of the beam extents in x and y (2,2 is the
        default).  For images with no beam characteristics there is no
        default, the units in this case are pixels.

Key: max
        Sets the maximum number of boxes to return, if more then max
        are detected then the max boxes with largest peak flux / pixel
        are returned.

Key: rad
        Will only report those islands detected within some angular
        radius of the specified coordinate pair.  The default units are
        absolute pixels, e.g. 16,18,10.  If units other than the default
        are used you must specify these after the radius, e.g.
        10:34:45.3,-45:54:02,0.005,hms,dms,degrees.

Key: options
        Extra processing options.  Possible values are:
 
        hist ....... compute the image pixel histogram and compute the
                     true image rms
        gauss ...... fit a Gaussian model to each component
        fixed ...... the FWHM is fixed (circular cross-section)
        point ...... a Gaussian with the characteristics of the point-
                     spread function is fit
        box ........ return the island box extents
        arcsec ..... output box BLC/TRC units are arcsec offset from
                     reference.  Default is absolute pixels.
        fiddle ..... interactively adjust the display lookup table
                     (LUT), and alter the transfer function.
        nofit ...... do not perform any fitting
        noplt ...... disable the plotting features
        nodet ...... skip island detection and fit the box given by
                     region - not implemented

Key: device
        PGPLOT plot device

Key: out
        Dataset to write fitted source parameters.  Each line of this
        file summarises the result of the Gaussian fit for one island.
        Each line contains:
 
        Island name, island number, ra and dec of island centroid,
        peak flux density, integrated flux density, deconvolved (from
        beam) major axis FWHM (arcsec), deconvolved minor axis (arcsec),
        deconvolved position angle (degrees), FLAG, DFLAG, FFLAG
 
        FLAG:   IFAIL value (an integer) means Gaussian fit did not
                  converge,
                F means failed to find covariance matrix for Gaussian
                  fit,
                N means it was not possible to attempt a Gaussian fit,
                C converged OK.
 
        DFLAG:  D  deconvolution of size from beam OK,
                P  deconvolution gave result close to point source,
                ?  No synthesised beam so could not deconvolve,
                F  deconvolution failed.
 
        FFLAG:  F  Integrated flux < peak flux (caused by beam > source
                   size).  If blank then ok.

Key: log
        If specified, output is written to the specified file instead of
        to the terminal.

Key: label
        Special purpose label