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NRAO Home > CASA > CASA Toolkit Reference Manual |
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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. Default is to use the full image.
| |
| allowed: | any |
|
| Default: | variant
|
|
mask |
| Mask to use. 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 |
|
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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