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image.findsources - Function

	Package	general
	Module	images
	Tool	image

Find point sources in the sky

Synopsis
findsources(nmax, cutoff, region, mask, point, width, negfind)

Arguments

nmax	in	Maximum number of sources to find
		Allowed:	Positive Integer
		Default:	20
cutoff	in	Fractional cutoff level
		Allowed:	Float
		Default:	0.1
region	in	The 2-D region of interest to fit
		Allowed:	Region tool
		Default:	Whole image
mask	in	OTF mask
		Allowed:	Boolean LEL expression or mask region
		Default:	None
point	in	Find only point sources ?
		Allowed:	T or F
		Default:	T
width	in	Half-width of fit grid when point=F
		Allowed:	Integer
		Default:	5
negfind	in	Find negative sources as well as positive ?
		Allowed:	T or F
		Default:	F

Returns
Componentlist tool or fail

Description

This function (short-hand name fs) finds strong point sources in the image. The sources are returned as 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) and the Imagefitter tool.

Example

- myim := imagemaketestimage()
- cl := myim.findsources(nmax=5, cutoff=0.5)
- cl.edit(1)

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