NRAO Home > CASA > CASA Toolkit Reference Manual
##### 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’,
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’);

###

__________________________________________________________________