1.1.1.0 image.findsources

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image.findsources - Function

1.1.1 Find point sources in the sky
Description

This function finds strong point sources in the image. The sources are returned in a record that can be used by a Componentlist tool.

An efficient method is used to locate sources under the assumption that they are point-like and not too close to the noise. Only sources with a peak greater than the cutoff fraction of the strongest source will be found. Only positive sources will be found, unless the negfind=T whereupon positive and negative sources will be found.

After the list of point sources has been made, you may choose to make a Gaussian fit for each one (point=F) so that shape information can be recovered as well. You can specify the half-width of the fitting grid with argument width which defaults to 5 (fitting grid would then be [11,11] pixels). If you set width=0, this is a signal that you would still like Gaussian components returned, but a default width should be used for the Gaussian shapes. The default is such that the component is circular with a FWHM of width pixels.

Thus, if point=T, the components in the returned Componentlist are Point components. If point=F then Gaussian components are returned.

The region-of-interest must be 2-dimensional and it must hold a region of the sky. Any degenerate trailing dimensions in the region are discarded.

See also the function fitsky (for which findsources can provide an initial estimate).

Arguments


Inputs
nmax	Maximum number of sources to find, ¿ 0
	allowed:	int
	Default:	20
cutoff	Fractional cutoff level
	allowed:	double
	Default:	0.1
region	The 2-D region of interest to fit. Default is whole image.
	allowed:	any
	Default:	record
mask	OTF mask, Boolean LEL expression or mask region. Default is none.
	allowed:	any
	Default:	variant
point	Find only point sources?
	allowed:	bool
	Default:	true
width	Half-width of fit grid when point=F
	allowed:	int
	Default:	5
negfind	Find negative sources as well as positive?
	allowed:	bool
	Default:	false

Returns
anyrecord

Example

"""
#
print "\t----\t findsources Ex 1 \t----"
ia.maketestimage()
clrec = ia.findsources(nmax=5, cutoff=0.5)
print clrec
#
"""

All sources stronger than 0.5 of the strongest will be found. We use the Componentlist GUI to look at the strongest component.

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