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Basic Information on 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
Information about the fit for each island is given.
The name of the input image data set.
The region of interest within the image (rectangular only).
Image intensity range to display. Default is min to max for the
current plane being displayed.
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
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.
Sets the maximum number of boxes to return, if more then max
are detected then the max boxes with largest peak flux / pixel
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.
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
PGPLOT plot device
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
F means failed to find covariance matrix for Gaussian
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.
If specified, output is written to the specified file instead of
to the terminal.
Special purpose label
Generated by firstname.lastname@example.org on 21 Jun 2016