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imager.approximatepsf - Function

2.3.1 Calculate approximate point spread functions


Description

Calculate the approximate point spread function. Note that the model visibilities are updated.

Some types of imaging do not yield a well-defined point spread function. For example, mosaicing or single dish imaging both yield point spread functions that are position dependent. Nevertheless, one can still usefully define an approximate PSF that is of some utility. This is calculated by doing the following calculation: a point source is located at the center of the specified coordinate system and the model data predicted. The approximate PSF is then formed from those model data using the full sky equation. For regular sampling in the image plane, this approximate PSF is actually quite good. It can be used in a deconvolution. For a mosaic with similar uv sampling per pointing, the approximate PSF is roughly the PSF per pointing multiplied by the primary beam. For a single dish image, it is roughly the telescope primary beam convolved with itself (if the gridfunction=’pb’ was selected).

Arguments





Inputs

psf

Name of output point spread function

allowed:

string

Default:

async

Run asynchronously in the background

allowed:

bool

Default:

false

Returns
bool

Example

 
Example of how to make the approximate psf for a mosaic:  
 
im.open(’orion.ms’)  
im.selectvis(spwid=[0, 1] ,field=range(2,11));  
im.defineimage(nx=300, ny=300, cellx=’2.0arcsec’,celly=’2.0arcsec’ , stokes="I", phasecenter=6, spwid=[0,1])  
im.weight(’natural’)  
im.setvp(dovp=T, usedefaultvp=True)  
im.setoptions(ftmachine=’mosaic’, padding=1.0)  
im.approximatepsf(psf=’LePSF.image’)  
 

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