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imager.advise  Function
2.3.1 Advise (and optionally use) parameter values
Description
Advise on recommended values of certain parameters. Return these values and
optionally use them in Imager.
The calculations are performed as following:
 cell
 The maximum uv distance in wavelength is found and then half of the inverse is taken as the maximum cellsize allowed.
 pixels
 The field of view is converted to a number of pixels using the calculated cell size.
 facets
 The number of facets on an axis is calculated in two different ways. The first
method simply requires that the peeling of facets away from the celestial
sphere should not cause an amplitude drop of more than the argument
amplitudeloss. The positions may be incorrect, but all the sources will
be removed correctly. The second method requires that the source
positions be accurate to the same fraction of the beam specified by
amplitudeloss. The second calculates the second moment in w and in
uv distance and chooses the number of facets correspondingly. The
first method does the same but after fitting a plane to the sampling:
w = au + bv. For an approximately coplanar array, the positions may be wrong
but the removal of sidelobes will be accurate. The number of facets
returned is the second, usually smaller, number. The formula used
is:
(2.2) where Δθ is the cellsize in radians, and δA is the amplitude loss. This formula can be derived from (a) the peeling of facets from the celestial sphere, and (b) a quadratic approximation for the beam size both in the plane of the sky and along the w axis.
Arguments
Outputs 
 
pixels 
 Number of pixels on a side
 
 allowed:  int  
 Default:  
cell 
 Recommended maximum cellsize  
 allowed:  record 

 Default: 
 
facets 
 Recommended number of facets on one axis
 
 allowed:  int  
 Default:  
phasecenter 
 Direction of phase center as a measure
 
 allowed:  string 

 Default: 


Inputs 
 
takeadvice 
 Use the advised values?
 
 allowed:  bool 

 Default:  true 

amplitudeloss 
 Maximum fractional amplitude loss due to faceting
 
 allowed:  double 

 Default:  0.05 

fieldofview 
 Desired field of view
 
 allowed:  any 

 Default:  variant 1.0deg 

bool
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