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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 fitcomponents (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

Region selection. See ”help par.region” for details. Default is to use the full image.

allowed:

any

Default:

variant

mask

Mask to use. See help par.mask. 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
record

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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