imager.feather - Function

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

Synopsis feather(image, highres, lowres, lowpsf, async)

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

`image`	`in`	Name of output feathered image
		`Allowed:`	`Image`
		`Default:`	`'feathered.image'`
`highres`	`in`	Name of high resolution (interferometer) image
		`Allowed:`	`Image`
`lowres`	`in`	Name of low resolution (single dish) image
		`Allowed:`	`Image`
`lowpsf`	`in`	Name of optional low resolution point spread function
		`Allowed:`	`Image`
`async`		Run asynchronously in the background
		`Allowed:`	`Bool`
		`Default:`	`!dowait`

Returns Bool

Example

####Please note that if you have both the images from somewhere else
####then one can just create imager without an ms
imgr:=imager(); 

###else one would use the imager that one used to deconvolve the
###interferometer data say
######
imgr.setvp(dovp=T, usedefaultvp=T)
imgr.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 aips++ 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 (setimage etc) then before feathering
imgr.setvp(dovp=T, usedefaultvp=F, vptable='bonn.pb')
imgr.feather(image='feathered.image', highres='casa.vlaonly',
lowres='casa.sd');

###

Next: imager.filter - Function Up: imager - Tool Previous: imager.exprmask - Function Contents Index

	`Package`	`synthesis`
	`Module`	`imager`
	`Tool`	`imager`