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imager.feather - Function

2.3.1 Feather together an interferometer and a single dish image in the Fourier plane


Description

Basically the ”imerg” algorithm of AIPS and SDE, or the ”feather” algorithm of MIRIAD, we regrid the total power (or low resolution) image onto the interferometer (or high resolution) image, Fourier transform both the interferometer and single dish images, down weight the Fourier transform of the interferometer image by 1.0 - FT(low res psf), add the weighted interferometer Fourier plane to the single dish Fourier plane, and transform back into the image plane.

The tapering is by the transform of a point spread function. If lowpsf is specified, that image is used, otherwise the appropriate telescope beam is used. The point spread function for a single dish image may be calculated using makeimage.

Advice: Note that if you are feathering large images, you’d be advised to have the number of pixels along the X and Y axes to be composite numbers and definitely not prime numbers. In general FFTs work much faster on even and composite numbers. You may use subimage function of image tool to trim the number of pixels to something desirable.

Arguments





Inputs

image

Name of output feathered image

allowed:

string

Default:

highres

Name of high resolution (interferometer) image

allowed:

string

Default:

lowres

Name of low resolution (single dish) image

allowed:

string

Default:

lowpsf

Name of optional low resolution point spread function

allowed:

string

Default:

effdishdiam

Optional new SD dish diameter in m to use in feathering; can be smaller than true dish size

allowed:

double

Default:

-1.0

lowpassfiltersd

Reject the high spatial frequency of the SD image

allowed:

bool

Default:

false

async

Run asynchronously in the background

allowed:

bool

Default:

false

Returns
bool

Example

 
 
im.setvp(dovp=True, usedefaultvp=True)  
im.feather(image=’feathered.image’, highres=’casa.vlaonly’,  
lowres=’casa.sd’);  
 
In the above example its using the default beams and the observatory  
information is in the image header.  
 
But if you have a single dish image with a beam which is not defined  
in the casa database then the example below is a guide of how to do  
that, say you know the beam of the single dish as a gaussian.  
 
 
 
#create a beam pattern table using vpmanager  
include ’vpmanager.g’  
vpman=vpmanager();  
vpman.setpbgauss(telescope=’OTHER’, othertelescope=’BONN’,  
halfwidth=’1arcmin’, maxrad=’20arcmin’, reffreq=’1.4GHz’);  
vpman.saveastable(’bonn.pb’)  
vpman.done()  
 
##....would have done  your usual imager setup (defineimage etc) then before feathering  
im.setvp(dovp=True, usedefaultvp=false, vptable=’bonn.pb’)  
im.feather(image=’feathered.image’, highres=’casa.vlaonly’,  
lowres=’casa.sd’);  
 
###  
 
 
 

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